prestressed concrete

State-of-the-Art Report

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Curved Precast Concrete Bridges

S t a t e - o f - t h e - A r t R e p o r t

P r e c a s t / P r e s t r e s s e d C o n c r e t e I n s t i t u t e

C o m m i t t e e o n B r i d g e s P u b l i c a t i o n C B - 0 1 - 1 2

F i r s t E d i t i o n

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Curved Precast Concrete Bridges

State-of-the-Art Report

Publication CB-01-12

Precast/Prestressed Concrete Institute

200 West Adams Street, Suite 2100

Chicago, IL 60606-5230

Phone: 312-786-0300 Fax 312-621-1114 www.pci.org

PCI Publication CB-01-12

First Edition 2012

Copyright © 2012

By Precast/Prestressed Concrete Institute

All rights reserved. No part of this book may be reproduced in any form without the written permission of the Precast/Prestressed Concrete Institute, except by a reviewer who wishes to quote brief passages in a review

written for inclusion in a magazine or newsletter.

ISBN 978-0-9853079-8-1

Cover Photo: I-70/SH 58 Flyover Ramp A, Denver, Colo. Owner: Colorado Department of Transportation, Denver, Colo. Photo: Gregg Reese, Summit Engineering Group, Littleton, Colo.

Printed in the United States of America

This document has been prepared and reviewed through an extensive Precast/Prestressed Concrete Institute (PCI) Committee process to present state-of-the-art information on

curved precast concrete bridges. Substantial effort has been made to ensure that all collected data and information included in this report are accurate. PCI, the committee

members, the authors, and the quoted agencies cannot accept responsibility for any errors or oversights in this report, the use of this material, or in the preparation of any design and engineering plans. This document is intended for reference by professional personnel who are competent to evaluate the significance and limitations of its contents and who are able to accept responsibility for the application of the material it contains. Actual conditions on

any project must be given special consideration and more specific evaluation and engineering judgment may be required that are beyond the intended scope of this work.

The contents do not necessarily reflect the official views or policies of the agencies mentioned, and do not constitute a standard or policy for design or construction.

iii (Oct 12)

FOREWORD

Precast, prestressed concrete has been used extensively in the nation’s highway bridges beginning in 1949. The vigorous construction of the interstate highway system beginning in the 1950s, resulted in the creation of new products and the subsequent development of higher performance materials and methods. Today, precast, prestressed concrete is recognized as the most durable and cost-effective bridge construction solution for the span ranges in which it is applicable.

Girders are manufactured in sophisticated, PCI-certified plants on permanent long-line casting beds in strong, accurate steel forms. The plants use high-strength, high-performance concrete that assures rapid fabrication cycles and excellent long-term performance. They use pretensioning to prestress the girders.

For more than 60 years, straight girders have been used to economically construct curved bridges. The girders form chords under the curved, cast-in-place concrete decks. Innovation has led to girder segments being spliced within spans to frame bridges with shorter radius curvatures.

Throughout the history of the industry, unique projects have been constructed that demonstrate the viability of casting curved precast concrete girders. Several of these have been used on transit guideways. Some have necessitated shipping curved girders over extensive distances. All have required stringent fabrication and construction tolerances.

A project completed in 1983 in Philadelphia, Pa., and one in 1995 in Denver, Colo., began the evolution of thinking about using curved girders for highway bridges. Numerous projects have been built since 2005. Many of these projects are described in this report. Analysis and design concepts are discussed. Construction issues are presented. References are provided for further reading.

In 2006, the PCI Bridge Committee recognized the need to gather and disseminate information about curved precast concrete bridges and especially curved girder technology. The information was needed by practitioners throughout the industry including designers, manufacturers, and the owner agencies. In that year, they established the PCI Curved Precast Bridges Subcommittee. Membership comprised a select group of industry stakeholders and consulting membership added a larger number of contributors. The subcommittee has been meeting in formal sessions at least twice each year since 2006.

PCI is recognized as the organization that develops and maintains the body of knowledge of the precast and precast, prestressed concrete industry. Since 1954, PCI has researched, refined, and published the technology of this industry. PCI developed comprehensive guidelines and standards for drafting, design, production, quality control, and installation of precast concrete. It administers the industry’s first and most comprehensive family of certification programs for personal, production, and erection of precast concrete―all of which are predicated on a continuous process of quality improvement.

This document adds to the body of knowledge for precast concrete, extending the application of conventional products to a specialized highway bridge solution. PCI will continue to develop this technology and expand its coverage and detail to provide guidance to practitioners on the applications, design, fabrication, and construction of curved concrete bridges.

Suggestions, questions, and comments concerning this document are welcome. Please contact Managing Director Transportation Systems at PCI; telephone 312-786-0300, or send your email to [email protected].

iv (Oct 12)

DEVELOPMENT AND REVIEW

Throughout the development of this document, strict adherence to the PCI policies has been followed, including a series of reviews. The outline and each draft were reviewed by the Curved Precast Bridges Subcommittee and its consulting members who replied with written comments. These comments were generally discussed at the semi- annual meetings of the subcommittee. The subcommittee balloted the final draft and all written comments were accommodated. The PCI Bridge Committee read and balloted the final draft. The document was submitted to the PCI Technical Activities Council (TAC) for assurance that it meets the Institute’s standards for technical content and quality guidelines for presentation. Primary and secondary comments resulting from the TAC ballot were resolved by the subcommittee.

ACKNOWLEDGEMENTS

Over the several years of development, many others in addition to the subcommittee engaged in discussions at the meetings and read one or more of the progression of drafts. PCI wishes to thank all of these professionals for their time and expertise. Many of those who participated in the writing and review of this document are acknowledged below.

Gregg Reese, president, Summit Engineering Group, furnished a great deal of material for this report. Unless specifically otherwise identified, drawings and photos were provided courtesy of Summit Engineering Group.

The following is a list of the active Voting Members of the PCI Curved Precast Bridges Subcommittee at the time this document was printed.

Mary Lou Ralls, Chair Ralls Newman, LLC

William N. Nickas, Non-voting Precast/Prestressed Concrete Institute

Christine Bulvan, Non-voting Precast/Prestressed Concrete Institute

Johann Aakre HNTB Corporation

Reid W. Castrodale Carolina Stalite Company

John S. Dick J. Dick Precast Concrete Consultant, LLC

Jamal Elkaissi Federal Highway Administration (Colorado Department of Transportation, Retired)

Morad G. Ghali Atkins USA

Juan Goni Garcia Bridge Engineers

R. Jon Grafton U.S. Concrete Precast Group/Pomeroy

James S. Guarre BergerABAM Inc.

Troy M. Jenkins Northeast Prestressed Products, LLC

Mike Jones Jones & Gardner Engineering, Inc

Michael McMullen Consultant (Colorado Department of Transportation, Retired)

Andrew D. Mish EnCon United

Andrzej S. Nowak University of Nebraska

Scott Phelan Buckland & Taylor, Ltd.

Gregg A. Reese Summit Engineering Group

Carin L. Roberts-Wollmann Virginia Polytechnic Institute and State University

Chuanbing Sun e.Construct.USA, LLC

Teddy S. Theryo Parsons Brinckerhoff, Inc.

Edward P. Wasserman Modjeski and Masters

Toorak Zokaie California Department of Transportation

v (Oct 12)

The following are Consulting Members of the PCI Curved Precast Bridges Subcommittee. Consulting Members are not held to the same strict attendance standards for Voting Members as set forth in the PCI Group Operating Manual. Many of these members attended numerous meetings and participated in committee work including verbal and written reviews of the documents.

Tess Ahlborn Michigan Technological University

Alex Aswad Consultant

Gregory Aaron Banks BergerABAM Inc.

James M. Barker HNTB Corporation, Retired

Paul Barr Utah State University

Oguzhan Bayrak University of Texas at Austin

Shrinivas Bhide Bentley Systems, Inc.

Dean Bierwagen Iowa Department of Transportation

Ned H. Burns University of Texas at Austin, Retired

Vijay Chandra Parsons Brinckerhoff, Inc.

Benxian Chen Houston Metropolitan Transit Authority

David Deitz Palmer Engineering

Daniel L. Dorgan HDR, Inc.

Timothy R. Eckert DMJM Harris/AECOM

Kevin R. Eisenbeis Burns & McDonnell

Larry A. Erickson SRF Consulting Group, Inc.

Roy L Eriksson Eriksson Technologies, Inc.

D. Scott Eshleman Consultant

Hussam (Sam) Fallaha Florida Department of Transportation

Matt Farrar Idaho Transportation Department

Ghulam Mujtaba Florida Department of Transportation, Retired

Donald J. Flemming URS Corp.

Lyman D. Freemon Consultant

Antonio M. Garcia Garcia Bridge Engineers

Hossein Ghara Louisiana Department of Transportation and Development

Ziad Hanna Alfred Benesch & Company

Joseph L. Hartmann Federal Highway Administration

Shane A. Hennessey Consultant

Susan E. Hida California Department of Transportation

Christopher D. Hill Consultant

David Hohmann HDR, Inc.

Jay Holombo

Finn Hubbard HNTB Corporation

Hamid Ikram Bentley Systems, Inc.

H. Hubert Janssen AECOM

Bruce Johnson Oregon Department of Transportation

Keith Kaufman Knife River Prestress

Bijan Khaleghi Washington State Department of Transportation

Takahiko Kimura Parsons Brinckerhoff, Inc.

Andy Ko Dewberry

Kosal Krishnan AECOM

Todd A. Lang HDR Inc

Michael D. LaViolette Michael Baker Corporation

Z. John Ma The University of Tennessee Knoxville

Tom Macioce Pennsylvania Department of Transportation

Eric E. Matsumoto California State University

Michael L. McCool, Jr. Beam, Longest & Neff, L.L.C.

Dennis Mertz University of Delaware

Richard A. Miller University of Cincinnati

Mark Moore Wiss, Janney, Elstner Associates, Inc.

Glenn C. Myers PBS&J

Claude S. Napier, Jr. Virginia Department of Transportation

Robert J. Peterman Kansas State University

vi (Oct 12)

Consulting Members of the PCI Curved Precast Bridges Subcommittee, continued Chuck Prussack Central Pre-Mix Prestress Co.

Basile G. Rabbat Consultant

Mark W. Richardson New Hampshire Department of Transportation

Loren Risch Kansas Department of Transportation

Steve Schwarz Prestress Engineering Company, LLC

Stephen J. Seguirant Concrete Technology Corporation

Rita Seraderian PCI Northeast

Jeffrey L. Smith

Eric Steinberg Ohio University

Mario G. Suarez Mario G. Suarez, P.E.

C. Douglas Sutton Purdue University

Maher K. Tadros e.Construct.USA, LLC

Benjamin Tang Oregon Department of Transportation

Michelle Tragesser KPFF Consulting Engineers

Raj Valluvan California Department of Transportation

Adel Zaki SNC-LAVALIN

Wael Zatar Marshall University

Stephen Zendegui Jacobs Inc.

CURVED PRECAST CONCRETE BRIDGES____________________________________________INFORMATION FOR USERS

vii (Oct 12)

INFORMATION FOR USERS

U1.0 ABOUT THIS DOCUMENT

This document is available as an electronic “eBook” and in a hardcopy version only after a personal eBook version is registered. The electronic version is a secured PDF format that is particularly useful because it can be searched and contains links to other material. It is fully printable but cannot be moved to another user. PCI uses Adobe Digital Edition software that is the same tried and proven software used by the public library system for secured document delivery.

U1.1 STRUCTURE OF THE DOCUMENT

U1.1.1 Using Links Links are provided from the Table of Contents to all numbered sections. The user may conveniently jump to a page number or to a section number. Links are provided to the websites of many of the cited references and to topics for additional information.

U1.1.2 Numbered Paragraphs Each main section in the text is identified with a decimal numbering system similar to the familiar system used for various AASHTO Specifications and the PCI Bridge Design Manual. This is the system used to organize this page you are reading. The hierarchy of the system is also apparent by the type size and font used in the titles of the sections.

U1.1.3 Page Header The header on every page identifies the chapter number, the chapter title, and the title of the document.

U1.1.4 Page Footer The lower right corner shows the month and year of publication. In the center is the page number. Revised pages will show “a,” “b,” etc. following the page number and a new date in the right corner. This method will be useful to determine the most current revision.

U1.1.5 Figures and Tables All figures and tables are numbered to the section where they first appear. Example: Figure 3.2.-1 is found in Section 3.2 and Figure 3.2-2 is the second figure to appear in the same section. Figures and tables referenced in the text are in bold type.

U1.2 REVISIONS AND REGISTRATION

Revisions to this document are expected. To receive revisions, or notices of revisions, it is required to register your copy of the Report.

U1.2.1 Registering Your Copy There is no cost or obligation to be registered. Those obtaining an eBook through the PCI ePub website will be automatically registered to the email address registered with Adobe and the PCI ePub fulfillment system.

U1.2.2 Errors and Omissions Your help will be appreciated in locating errors and identifying omissions. Please contact PCI with your suggestions at [email protected].

CURVED PRECAST CONCRETE BRIDGES____________________________________________INFORMATION FOR USERS

viii (Oct 12)

UI 1.2.3 Dissemination of Corrections Corrections to this document if required will be assembled and a notice emailed to those registered. The replacement pages will readily identify the change and the page will be identified as revised in the footer.

Two methods are used to disseminate changes. Simple corrections, revisions, and improvements will be posted as “Errata” on the PCI Publications website, http://www.pci.org/cms/index.cfm/publications/errata. Or, select “Errata” on the Publications home page, then look for the title of this document.

Complex revisions that involve more than a few pages may require the user to redownload the entire document. There will be no cost for this download. Instructions will be emailed as noted above.

In the future, when a new edition is required, an email will notify registered users. There will likely be an additional charge for a new edition. Please keep your contact information current so you can be notified.

U1.3 EXCHANGE OF SUGGESTIONS

U1.3.1 Send Your Suggestions Your suggestions and comments concerning this document will be greatly appreciated. Call, write or e-mail to “Bridge Engineer” at the location and telephone number on the inside cover page, or email [email protected].

UI 1.3.2 Our Suggestion We strongly urge the designer, in the early stages of a project, to contact one or more PCI-certified precast concrete manufacturers. The manufacturer can advise about local experience and capability. The producer can often help with suggested solutions and cost estimates. They can provide specific design information about special local, state or regional precast sections. A current list of PCI-certified producers is readily available on the PCI website at www.pci.org.

CURVED PRECAST CONCRETE BRIDGES____________________________________________________TABLE OF CONTENTS

ix (Oct 12)

TABLE OF CONTENTS

1.0 INTRODUCTION ................................................................................................................................................................................................ 1

1.1 BACKGROUND .................................................................................................................................................................................................... 1

1.2 PRECAST CONCRETE SOLUTIONS ............................................................................................................................................................ 1

1.3 ORGANIZATION OF THIS REPORT ............................................................................................................................................................ 1

2.0 STRAIGHT GIRDERS CHORDED FROM PIER TO PIER ...................................................................................................................... 2

2.1 INTRODUCTION AND BACKGROUND ...................................................................................................................................................... 2

2.2 AESTHETICS ........................................................................................................................................................................................................ 3

2.3 DESIGN AND ANALYSIS CONSIDERATIONS ......................................................................................................................................... 4

2.4 FRAMING AND CONNECTION CONSIDERATIONS ............................................................................................................................. 5

2.5 FABRICATION, TRANSPORTATION, AND ERECTION ...................................................................................................................... 6

2.5.1 Fabrication .................................................................................................................................................................................................. 6

2.5.2 Transportation and Erection .............................................................................................................................................................. 6

2.6 COST CONSIDERATIONS ............................................................................................................................................................................... 7

2.7 PROJECT STUDIES ............................................................................................................................................................................................ 7

2.7.1 SR 50 Bridge over Happy Hollow Creek ........................................................................................................................................ 7

2.7.1.1 Project Information ........................................................................................................................................................................ 7

2.7.1.2 Structural System ............................................................................................................................................................................ 7

2.7.1.3 Construction ................................................................................................................................................................................... 10

2.7.1.4 Lessons Learned ........................................................................................................................................................................... 10

2.7.2 PHX Sky Train™ Guideway Bridge ................................................................................................................................................. 10

2.7.2.1 Project Information ..................................................................................................................................................................... 10

2.7.2.2 Structural System ......................................................................................................................................................................... 10

2.7.2.3 Construction ................................................................................................................................................................................... 12

2.7.2.4 Lessons Learned ........................................................................................................................................................................... 13

3.0 STRAIGHT GIRDER SEGMENTS WITH SPLICES WITHIN THE SPANS ................................................................................... 13

3.1 INTRODUCTION AND BACKGROUND ................................................................................................................................................... 13

3.2 AESTHETICS ..................................................................................................................................................................................................... 14

3.3 DESIGN AND ANALYSIS CONSIDERATIONS ...................................................................................................................................... 16

3.3.1 Geometric Constraints ........................................................................................................................................................................ 18

3.3.2 Lateral Loadings Due to Post-Tensioning .................................................................................................................................. 20

3.3.3 Loadings Due to Curvature ............................................................................................................................................................... 22

3.3.4 Summary of Design and Analysis ................................................................................................................................................... 23

3.4 DETAILS ............................................................................................................................................................................................................. 24

3.5 FABRICATION, TRANSPORTATION, AND ERECTION ................................................................................................................... 27

3.5.1 Fabrication ............................................................................................................................................................................................... 27

3.5.2 Transportation ....................................................................................................................................................................................... 28

3.5.3 Erection ..................................................................................................................................................................................................... 28

CURVED PRECAST CONCRETE BRIDGES____________________________________________________TABLE OF CONTENTS

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3.5.3.1 Requirement for Licensed Construction Engineer ........................................................................................................ 28

3.6 COST CONSIDERATIONS ............................................................................................................................................................................ 28

3.7 PROJECT STUDIES ......................................................................................................................................................................................... 29

3.7.1 Rosebank Pataki Interchange Bridges ......................................................................................................................................... 29

3.7.1.1 Project Information ..................................................................................................................................................................... 29

3.7.1.2 Structural System ......................................................................................................................................................................... 29

3.7.1.3 Construction ................................................................................................................................................................................... 31

3.7.1.4 Lessons Learned ........................................................................................................................................................................... 31

3.7.2 I-70 Elevated Viaduct over Washington Street and BNSF Railroad ............................................................................... 31

3.7.2.1 Project Information ..................................................................................................................................................................... 31

3.7.2.2 Structural System ......................................................................................................................................................................... 31

3.7.2.3 Construction ................................................................................................................................................................................... 34

3.7.2.4 Lessons Learned ........................................................................................................................................................................... 34

3.7.3 Bijou Street over Monument Creek ............................................................................................................................................... 34

3.7.3.1 Project Information ..................................................................................................................................................................... 34

3.7.3.2 Structural System ......................................................................................................................................................................... 34

3.7.3.3 Construction ................................................................................................................................................................................... 35

3.7.3.4 Lessons Learned ........................................................................................................................................................................... 35

4.0 CURVED GIRDERS ......................................................................................................................................................................................... 36

4.1 INTRODUCTION AND BACKGROUND ................................................................................................................................................... 36

4.2 AESTHETICS ..................................................................................................................................................................................................... 36

4.3 DESIGN AND ANALYSIS CONSIDERATIONS ...................................................................................................................................... 37

4.3.1 Cross-Section Geometry ..................................................................................................................................................................... 37

4.3.2 Span Length and Girder Segment Length ................................................................................................................................... 38

4.3.3 Lateral Bracing ....................................................................................................................................................................................... 38

4.3.4 Post-tensioning ...................................................................................................................................................................................... 40

4.3.5 Temporary Supports ........................................................................................................................................................................... 41

4.3.5.1 Requirement for Licensed Construction Engineer ........................................................................................................ 42

4.4 DETAILS ............................................................................................................................................................................................................. 42

4.5 FABRICATION, TRANSPORTATION, AND ERECTION ................................................................................................................... 46

4.5.1 Fabrication ............................................................................................................................................................................................... 46

4.5.1.1 Forms ................................................................................................................................................................................................. 46

4.5.1.2 Precasting ........................................................................................................................................................................................ 47

4.5.2 Transportation and Erection ........................................................................................................................................................... 48

4.5.2.1 Girder Stability............................................................................................................................................................................... 50

4.6 COST CONSIDERATIONS ............................................................................................................................................................................ 52

4.7 PROJECT STUDIES ......................................................................................................................................................................................... 52

4.7.1 Seattle Monorail ..................................................................................................................................................................................... 52

4.7.1.1 Project Information ..................................................................................................................................................................... 52

CURVED PRECAST CONCRETE BRIDGES____________________________________________________TABLE OF CONTENTS

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4.7.1.2 Structural System ......................................................................................................................................................................... 52

4.7.1.3 Construction ................................................................................................................................................................................... 53

4.7.1.4 Lessons Learned ........................................................................................................................................................................... 53

4.7.2 Disney World Monorail ...................................................................................................................................................................... 53

4.7.2.1 Project Information ..................................................................................................................................................................... 53

4.7.2.2 Structural System ......................................................................................................................................................................... 54

4.7.2.3 Construction ................................................................................................................................................................................... 54

4.7.2.4 Lessons Learned ........................................................................................................................................................................... 54

4.7.3 Las Vegas Monorail............................................................................................................................................................................... 54

4.7.3.1 Project Information ..................................................................................................................................................................... 54

4.7.3.2 Structural System ......................................................................................................................................................................... 55

4.7.3.3 Construction ................................................................................................................................................................................... 55

4.7.3.4 Lessons Learned ........................................................................................................................................................................... 55

4.7.4 Expo 86 Vancouver SkyTrain ........................................................................................................................................................... 55

4.7.4.1 Project Information ..................................................................................................................................................................... 55

4.7.4.2 Structural System ......................................................................................................................................................................... 56

4.7.4.3 Construction ................................................................................................................................................................................... 56

4.7.4.4 Lessons Learned ........................................................................................................................................................................... 56

4.7.5 Detroit Central Area Transit System ............................................................................................................................................ 56

4.7.5.1 Project Information ..................................................................................................................................................................... 56

4.7.5.2 Structural System ......................................................................................................................................................................... 57

4.7.5.3 Construction ................................................................................................................................................................................... 57

4.7.5.4 Lessons Learned ........................................................................................................................................................................... 57

4.7.6 Getty Center Tram Guideway........................................................................................................................................................... 58

4.7.6.1 Project Information ..................................................................................................................................................................... 58

4.7.6.2 Structural System ......................................................................................................................................................................... 58

4.7.6.3 Construction ................................................................................................................................................................................... 60

4.7.6.4 Lessons Learned ........................................................................................................................................................................... 60

4.7.7 I-95 Airport Ramp Bridge .................................................................................................................................................................. 60

4.7.7.1 Project Information ..................................................................................................................................................................... 61

4.7.7.2 Structural System ......................................................................................................................................................................... 61

4.7.7.3 Construction ................................................................................................................................................................................... 62

4.7.7.4 Lessons Learned ........................................................................................................................................................................... 63

4.7.8 Arbor Road Bridge ................................................................................................................................................................................ 63

4.7.8.1 Project Information ..................................................................................................................................................................... 63

4.7.8.2 Structural System ......................................................................................................................................................................... 63

4.7.8.3 Construction ................................................................................................................................................................................... 64

4.7.8.4 Lessons Learned ........................................................................................................................................................................... 65

4.7.9 Curved Precast U-Girder Projects in Colorado ......................................................................................................................... 65

CURVED PRECAST CONCRETE BRIDGES____________________________________________________TABLE OF CONTENTS

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4.7.9.2 Construction ................................................................................................................................................................................... 68

4.7.9.3 Lessons Learned ........................................................................................................................................................................... 68

5.0 NEEDED RESEARCH AND CONCLUSION ............................................................................................................................................. 69

5.1 FUTURE RESEARCH...................................................................................................................................................................................... 69

5.2 CONCLUSION ................................................................................................................................................................................................... 70

6.0 CITED REFERENCES ..................................................................................................................................................................................... 71

CURVED PRECAST CONCRETE BRIDGES______________________________________LIST OF FIGURES AND TABLES

xiii (Oct 12)

LIST OF FIGURES

Figure 2.1-1 Radial Substructures with Chorded, Variable-Length Girders .................................................................................. 3

Figure 2.1-2 Parallel Substructures with Chorded, Equal-Length Girders ..................................................................................... 3

Figure 2.2-1 Girder Length versus Radii of Curvature for Various Offsets .................................................................................... 4

Figure 2.7.1.2-1 Aerial View of Happy Hollow Creek Bridge ................................................................................................................ 8

Figure 2.7.1.2-2 Typical Cross Section—Happy Hollow Creek Bridge ............................................................................................. 8

Figure 2.7.1.2-3 Elevation and Plan Views of Happy Hollow Creek Bridge ................................................................................... 9

Figure 2.7.2.2-1 Elevation View of PHX Sky Train Guideway ............................................................................................................ 10

Figure 2.7.2.2-2 PHX Sky Train Guideway Cross Section .................................................................................................................... 11

Figure 2.7.2.2-3 Partial Plan View of U-Girder Layout—PHX Sky Train Guideway................................................................. 12

Figure 3.1-1 Rosebank Pataki Bridge during Construction ................................................................................................................ 13

Figure 3.1-2 Partial Framing Plan—Rosebank Pataki Bridge ........................................................................................................... 14

Figure 3.2-1 Completed Rosebank Pataki Bridge ................................................................................................................................... 15

Figure 3.2-2 Bijou Street Bridge in Colorado Springs, Colo. ............................................................................................................... 16

Figure 3.3-1 Temporary Shores and Hangers Support Precast Segments during Construction on the Rosebank Pataki Bridge ........................................................................................................................................................................................................... 17

Figure 3.3-2 Temporary Hangers Used in a Curved, Spliced, U-Girder Bridge during Construction .............................. 17

Figure 3.3.1-1 Comparison of Framing Plans for Spliced Girder and Simple-Span Bridges ................................................ 18

Figure 3.3.1-2 Straight Girder Offsets from Horizontally Curved Alignments ........................................................................... 19

Figure 3.3.1-3 Framing Plan for the I-70 Viaduct over Washington Street in Denver, Colo. ............................................... 20

Figure 3.3.1-4 Framing Plan for the Bijou Street Bridge in Colorado Springs, Colo. ............................................................... 20

Figure 3.3.2-1 Lateral Loads from Post-Tensioning at Girder Splices ........................................................................................... 21

Figure 3.3.2-2 Analysis of Lateral Post-Tensioning Loads on a Three-Span Curved Bridge ............................................... 21

Figure 3.3.2-3 Transverse Diaphragms at Kinked Splices in the I-70 Washington Street Bridge ..................................... 22

Figure 3.3.3-1 Gravity Load Moments in a Three-Span Curved Bridge ........................................................................................ 23

Figure 3.3.3-2 Gravity Load Torsional Moments in a Three-Span Curved Bridge ................................................................... 23

Figure 3.4-1 Longitudinal Post-Tensioning Layout for a Spliced Precast Concrete Girder Bridge .................................. 24

Figure 3.4-2 Pier and Drop-In Precast Girder Segment Details ........................................................................................................ 24

Figure 3.4-3 Longitudinal Post-Tensioning Anchorages Placed in an Abutment Diaphragm ............................................ 25

Figure 3.4-4 Plan and Section Views of a Transverse Diaphragm at Kinked Splices in the Bijou Street Bridge ........ 25

Figure 3.4-5 Transverse Diaphragm at a Kinked Splice in the Bijou Street Bridge ................................................................. 26

Figure 3.4-6 Kinked Splice Reinforcement Details at the Ends of Precast U-Girders ............................................................. 26

Figure 3.4-7 Transverse Diaphragms at Kinked Splices of I-Girders ............................................................................................. 27

Figure 3.7.1.2-1 Plan View of Ramps A and B, Rosebank Pataki Interchange ............................................................................ 29

Figure 3.7.1.2-2 Layout and Construction Sequence of Ramp B Girder Segments in Roadway Overcrossing ............ 30

Figure 3.7.1.2-3 Aerial View of Completed Ramp B, Rosebank Pataki Interchange ................................................................ 31

Figure 3.7.2.2-1 Framing Plan, I-70 Viaduct over Washington Street and the Platte River ................................................. 32

Figure 3.7.2.2-2 Framing Plan, I-70 Viaduct over 46th Avenue and the BNSF Railroad ....................................................... 32

CURVED PRECAST CONCRETE BRIDGES______________________________________LIST OF FIGURES AND TABLES

xiv (Oct 12)

Figure 3.7.2.2-3 I-70 Viaduct over Washington Street During Construction. The Cantilevered, Haunched Pier Segments are Shown in the Foreground. .................................................................................................................................................... 33

Figure 3.7.2.2-4 Typical Haunched Girder Cross Sections, I-70 Viaduct Bridges ..................................................................... 33

Figure 3.7.3.2-1 Completed Bijou Street Bridge ...................................................................................................................................... 34

Figure 3.7.3.2-2 Kinks at Splices in the Bijou Street Bridge ............................................................................................................... 35

Figure 4.2-1 Views of SH 58 Ramp A over I-70 in Golden, Colo. ...................................................................................................... 37

Figure 4.3.1-1 Typical Cross Sections Suitable for Curved Girder Construction ...................................................................... 37

Figure 4.3.3-1 Temporary Lateral Steel Bracing Installed in the Fabrication Plant ................................................................ 39

Figure 4.3.3-2 Curved U-Girders Shown Laterally Braced by Cast-in-Place Concrete Lid Slabs ....................................... 39

Figure 4.3.4-1 Example Girder Segment Arrangement and Post-Tensioning Layout ............................................................ 40

Figure 4.3.4-2 Longitudinal Post-Tensioning Details at the Ends of Various Precast Girder Segments ........................ 41

Figure 4.3.5-1 Erected Precast U-Girder Segments ................................................................................................................................ 41

a) Girder Segments Supported on Piers and Temporary Shoring Towers ............................................................................. 41

b) Haunched Girder Segments Supported on Piers and Temporary Structures Constructed with Simple Cast-In- Place Concrete Shoring Columns ............................................................................................................................................................... 41

Figure 4.3.5-2 Example Erection Bracing Details ................................................................................................................................... 42

Figure 4.4-1 End Diaphragms and Splice Details in Precast Girders ............................................................................................. 43

Figure 4.4-2 U-Girder Center of Rotation ................................................................................................................................................... 44

Figure 4.4-3 Precast Concrete Panels are used to close the Tops of the Girders and Span between Girders .............. 45

Figure 4.4-4 Precast Concrete Panels Cantilever to Form the Deck Overhang.......................................................................... 45

Figure 4.4-5 Partial-Depth Precast Concrete Deck Panels .................................................................................................................. 46

a) A Long-Line Steel Form Used to Cast and Prestress Deck Panels ......................................................................................... 46

b) Deck Panels in Storage in a Manufacturing Plant ......................................................................................................................... 46

Figure 4.4-6 U-Girder Closure Details Using Precast Concrete, Partial-Depth Deck Panels ................................................ 46

Figure 4.5.1.1-1 Exterior Form Used to Cast Curved Girders ............................................................................................................ 47

Figure 4.5.1.1-2 Chorded Interior Core Form for Casting Curved Girders .................................................................................. 47

Figure 4.5.1.2-1 Girder Cross Sections and Typical Reinforcement Details................................................................................ 48

Figure 4.5.2-1 Curved Girders Ready for Transport .............................................................................................................................. 49

Figure 4.5.2-2 Erection of Curved Girder Segments .............................................................................................................................. 49

Figure 4.5.2.1-1 The Offset from a Straight Line to the Face of a Curved Girder Segment at its Midpoint due to Curvature .................................................................................................................................................................................................................. 51

Figure 4.5.2.1-2 Lifting Details Showing a Typical Biased Spreader Bar ..................................................................................... 51

Figure 4.7.1.2-1 Monorail Transit System, Seattle, Wash. ................................................................................................................... 53

Figure 4.7.2.2-1 Disney World Monorail Transit System in Florida ............................................................................................... 54

a) Girders Supported on Columns ............................................................................................................................................................ 54

b) Girders Supported on Steel Crossheads ........................................................................................................................................... 54

Figure 4.7.3.2-1 Monorail Transit System in Las Vegas, Nev. ............................................................................................................ 55

Figure 4.7.4.2-1 Expo 86 SkyTrain Transit System in Vancouver, British Columbia, Canada ............................................ 56

Figure 4.7.5.2-1 Central Area Transit System in Detroit, Mich. ........................................................................................................ 57

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Figure 4.7.6.2-1 Aerial View of Getty Center Tram Guideway With the Access Road on the Right .................................. 58

Figure 4.7.6.2-2 A Portion of the Curved Getty Center Tram Guideway ....................................................................................... 59

Figure 4.7.6.2-3 Cross Section of the Getty Center Tram Guideway ............................................................................................... 59

Figure 4.7.6.3-1 A Section of Guideway with Two Curved L-Beams is shown During a Mock-Up in the Precast Plant. Precast Crossheads In the Foreground Have Troughs to Receive Precast Stem Beams. ...................................................... 60

Figure 4.7.7-1 Completed I-95 Philadelphia, Pa., Airport Ramp Bridge ....................................................................................... 61

Figure 4.7.7.2-1 Chorded Curved Girders in the I-95 Philadelphia, Pa., Airport Ramp Bridge .......................................... 62

a) Top View of Girders Shown During Construction ........................................................................................................................ 62

b) View From Under Curved Girders Prior to Casting Bridge Deck ........................................................................................... 62

Figure 4.7.7.2-2 Assembled and Post-tensioned Girder in the Precasting Plant ...................................................................... 62

Figure 4.7.8.2-1 Curved Rectangular Girders During Construction in the Arbor Road Bridge, Lancaster County, Neb. .............................................................................................................................................................................................................................. 63

Figure 4.7.8.2-2 Completed Arbor Road Bridge in Nebraska ............................................................................................................ 64

Figure 4.7.8.3-1 Full-Depth, Full-Width Precast, Prestressed Concrete Deck Panels on the Arbor Road Bridge ...... 65

Figure 4.7.9-1 Curved Concrete U-Girder Bridges in Colorado ........................................................................................................ 67

a) Austin Bluffs Parkway over Union Boulevard, Colorado Springs, Colo. ............................................................................. 67

b) I-25/SH 270 Ramp K, Denver, Colo. ................................................................................................................................................... 67

c) I-25 Viaduct, Trinidad, Colo. ................................................................................................................................................................... 67

d) I-70/SH 58 Ramp A, Golden, Colo. ....................................................................................................................................................... 67

e) I-25 Viaduct, Trinidad, Colo. ................................................................................................................................................................... 68

f) I-76/SH 270 Ramp Y, Denver, Colo. ..................................................................................................................................................... 68

g) C-470/I-70 Ramp H, Aurora, Colo. ...................................................................................................................................................... 68

h) C-470/Santa Fe Boulevard, Denver, Colo. ........................................................................................................................................ 68

LIST OF TABLES

Table 4.7.9-1 Summary of Curved Precast Concrete U-Girder Bridges in Colorado ............................................................... 66

Table 4.7.9-2 The Location and Owners of Curved Precast U-Girder Bridges in Colorado .................................................. 66

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CURVED PRECAST CONCRETE BRIDGES___________________________________________________________________CHAPTER 1

INTRODUCTION

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1.0 INTRODUCTION

1.1 BACKGROUND

Precast concrete girders have a history of use on roadways with curved alignments. Highway alignments generally dictate the location, length, and geometry of bridges. Where bridges occur on curved alignments such as at interchanges and curves on roadways, straight precast concrete girders have often been utilized. Curved roadway alignments and the degree of curvature vary significantly, from slight curvature with horizontal radii of curvature greater than 1,200 ft to sharp curvature with horizontal radii of curvature less than 800 ft. In the past, the design and construction of horizontally curved bridges, particularly with shorter radii, have typically used structural steel or cast-in-place concrete superstructures.

Welded steel plate girders and box girders have been used extensively on complex curved bridge structures. Speed of construction and maintenance of traffic considerations are typically factors in choosing structural steel girders to build curved bridges. Fluctuations in steel prices, availability of material, and extended fabrication times have affected the desire to use this design option.

Cast-in-place concrete has also been utilized to provide an economical solution for the construction of curved bridges. The use of cast-in-place concrete requires the challenge of how to maintain traffic and provide vertical clearances through the construction site while using “long-span” or continuous shoring. Historically, concrete box girders have been used on curved bridges to resist torsion and out-of-plane forces, provide a durable solution, and to enhance aesthetics.

1.2 PRECAST CONCRETE SOLUTIONS

Precast concrete has become a common design alternative to horizontally curved steel or cast-in-place concrete bridges. Precast concrete designs, ranging from simple pier-to-pier framing to more complex spliced, post- tensioned girder designs have been used to accommodate the full spectrum of curved bridge design situations. This state-of-the-art report describes current design practices for curved precast concrete girder bridges in three configurations:

 Curved bridges using straight girders chorded from pier to pier

 Curved bridges using spliced, straight girders with field splice points within the spans

 Curved bridges using curved girders

For each configuration, this report describes the background, aesthetics, design and analysis considerations, details, fabrication, transportation, erection, and cost considerations. Several example project studies are included.

1.3 ORGANIZATION OF THIS REPORT

Chapter 2 describes the least complex and, therefore, the most economical horizontally curved precast concrete girder bridges. Many curved bridges have been designed and constructed using straight precast, prestressed concrete girders that are chorded from pier to pier. A concrete deck is constructed to accommodate the curved roadway geometry. The deck may be cast in place, precast, or precast integrally with the girders. Curved bridges constructed with chorded precast concrete girders are designed much like straight bridges. Chapter 2 presents two project studies for curved bridges that have been designed and constructed with straight precast concrete girders spanning from pier to pier. In the first project study, the SR 50 Bridge over Happy Hollow Creek in Tennessee, the girders in each span are parallel to each other and equal in length, with a parallel, non-radial orientation of the substructure (i.e., variable skew). In the second project study, the PHX Sky Train™ Guideway Bridge at the Phoenix Sky Harbor Airport, the girders in each span are parallel to each other and unequal in length, with a radial orientation of the substructure.

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Chapter 3 describes curved precast concrete girder bridges at the next level of complexity. Curved bridges can be supported by straight precast concrete girders that have angle changes at field splices within the spans. The girders may be either pretensioned, post-tensioned, or both. This type of bridge is primarily used to provide for longer spans or sharper curvature. The number of splices is dependent on the length of the spans, the curvature of the bridge, or shipping and construction constraints. Chapter 3 presents three project studies. Each of these bridges utilized spliced, continuous, post-tensioned construction to meet various design constraints to produce an economical precast concrete girder-and-slab solution. The bridges are presented in chronological order of construction. The first project study is the Rosebank Pataki Interchange Bridges in Auckland, New Zealand (1997). The second and third project studies are in Colorado, the I-70 Elevated Viaduct over Washington Street and the BNSF Railroad (1999), and the Bijou Street Bridge over Monument Creek (2007).

Chapter 4 describes the most complex curved precast concrete bridges that utilize curved precast concrete girders. These girders are precast in a shape that matches the curved roadway geometry and can be either full span or field spliced within the span. This type of bridge is primarily used to provide an economical and aesthetic alternative to curved steel girder bridges and curved cast-in-place or segmental concrete bridges. This is the newest approach to curved precast concrete bridge design described in this report. Chapter 4 presents four project studies. The first study describes early people-mover monorail and transit bridges. The second project study, the I-95 Ramp Bridge to the Philadelphia, Pa., airport, is a short-span, multi-box girder bridge with sharp curvature. The third project study, the Arbor Road Bridge in Nebraska, is the first of the “modern” curved precast concrete girder highway bridges. The fourth project study, a collection of curved precast concrete girder bridges in Colorado, describes the latest state-of-the-practice for this technology in the United States.

2.0 STRAIGHT GIRDERS CHORDED FROM PIER TO PIER

2.1 INTRODUCTION AND BACKGROUND

The most simple and economical horizontally curved precast concrete bridges have curved deck edges on straight girders spanning between supports. Any precast girder section may be used on a horizontally curved bridge provided the offset between the outside girder and deck edge is acceptable. When the offset is large, the bridge appearance may be objectionable, or the overhang length may exceed requirements for crash resistance stated in the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications. In that case, the bridge may be designed to the next higher level of complexity—spliced straight girders with field splice points within the span as discussed in Chapter 3—or with continuously curved girders as discussed in Chapter 4.

The designer of a curved bridge with chorded girders has a variety of geometric layout options for framing plans and orientation of substructures. The most direct and common approach is to define the girders as chords of concentric arcs, rendering parallel, equidistant girders within each span. The substructures can be set radially, as shown in Figure 2.1-1, parallel to each other as shown in Figure 2.1-2, or any other combination of skews that may be convenient to equalize girder lengths to the extent possible, or to fit the geometric constraints of the site.

Barring any other considerations, it would be most efficient for all girders in the bridge or all girders in a span to be of equal length, as shown on the layout in Figure 2.1-2. However, this is not always possible. When the lengths of girders must vary from span to span or within a span, it is more cost effective for fabrication to have the same number and location of prestressing strands and end stirrup spacing patterns in all girders, as much as possible, to accommodate casting multiple girders in a single production line.

Substructures should be oriented to a reference line that is tangent to some convenient station along the designated curve, usually the centerline of the bridge deck.

In Figure 2.1-2, the designer has chosen to skew the ends of the girders to be parallel to the centerline of each substructure in Spans 1 and 3. This has the advantage of minimizing the width of the supporting substructure. However, fabrication is easier when the ends of the girder are square.

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It should also be noted in Figure 2.1-2, that the layout does not, in this case, allow the ends of girder lines at the common substructure to align. For simple-span bridges this is not problematic but may introduce complexities for continuous bridges with common diaphragms, as torsion will occur in the diaphragms.

Figure 2.1-1

Radial Substructures with Chorded, Variable-Length Girders

Figure 2.1-2

Parallel Substructures with Chorded, Equal-Length Girders

2.2 AESTHETICS

When straight prestressed girders are used on a horizontally curved roadway, the overhang distance must vary. Normally, the maximum deck overhang at the outside of the curve at the center of the long span will be made approximately equal to the overhang at the piers on the inside of the curve. The point of minimum overhang distance must accommodate the drip groove. When the curvature is extreme and the difference between maximum and minimum overhang distance becomes large, pier locations may need adjustment to reduce the span lengths.

Straight girders on sharply curved alignments may have a less than desirable appearance and also tend to become structurally less efficient. Figure 2.2-1 is a graph of girder length versus radius of curvature for offsets varying from 1.0 to 3.5 ft. Assuming a maximum overhang of 4.5 ft, a 1.0 ft offset provides overhangs varying from 3.5 ft to 4.5 ft. This variance is barely perceptible. For a 3.5 ft offset, the overhang varies from 1.0 to 4.5 ft, which is

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approaching an undesirable appearance. The wide range of girder lengths and curvatures shown in Figure 2.2-1 confirms that many curved bridge projects can be built by chording across the curve.

Figure 2.2-1

Girder Length versus Radii of Curvature for Various Offsets

2.3 DESIGN AND ANALYSIS CONSIDERATIONS

Straight precast, prestressed concrete girders have been used on many curved highway alignments for individual bridges as well as for ramps at interchanges. When such usage is anticipated, planning should begin at the conceptual or preliminary phases. The factors that affect the use of straight girders on curved alignments are:

 Radius of curvature

 Type of girder (e.g., box, T or I shapes)

 Provision for minimum overhang beyond the edge girder

 Avoiding excessive overhang beyond the top flange of the edge girder

 Interference of the flanges of adjacent spans at the piers

 Interference of the girder flanges with the back wall at the abutments

 Bearing locations with respect to tops of piers

 Location of expansion joint relative to top flanges of the girders

A layout of the alignment with superimposed girders is useful in identifying potential conflicts. Such a layout should include the top and bottom flanges of the girder as well as the ends of the girder over the piers and at the abutments. A detailed layout may be required at the piers or abutments to study the interference issues with adjoining girders or with the abutment back wall and required pier and abutment diaphragm reinforcement. The distance between the centerline of pier and center of girder bearings may need to be increased to avoid conflict between the bottom flanges of abutting girders. Alternatively, the girder ends may be partially skewed (clipped) to avoid conflict between the flanges and to accommodate continuity connections or expansion joints. Another solution is to fully skew the ends of the girders to match the skew of the pier centerline.

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Various considerations for curved bridges using straight girders are:

1. On curved roadways with flared widths, the girders may be placed at equal spacings at each end. If the

flare is slight, construction may be simplified by using parallel interior girders and flared exterior girders.

2. In each span, care should be taken during the layout process to avoid excessive overhangs at the ends of

the inside curves and at mid-span of the outside curves. The critical overhang length needs to be

considered to determine the load distribution of the exterior girder and the deck overhang design.

Additionally, it is recommended that the overhang dimension not exceed the girder depth for

convenience during construction in setting deck form brackets.

3. The designer must determine the girder spacing to use for dead load and live load design and whether a

refined analysis that considers actual load application is warranted. Typically, the girder spacing at the

center of a span can be used for girder design. Spans that are combinations of curves and tapers will

require special consideration to develop the most effective and economical girder arrangement. Girder

lengths and number of strands should be the same for as many girders as possible in each span to help

minimize fabrication cost.

4. Centrifugal force should be included in curved bridge analysis and applied horizontally at a distance of

6.0 ft above the roadway surface. The centrifugal force tends to cause increased vertical wheel loads

toward the outside of the curve and decreased vertical wheel loads toward the inside of the curve. A load

path to carry the radial force to the substructure should be provided. Providing diaphragms or shear

blocks between girders at support locations should be considered to transfer the shear forces to the

substructure.

5. Torsional forces resulting from curved bridges are often small, but the designer should not fail to

investigate these forces and their affect on the girders.

2.4 FRAMING AND CONNECTION CONSIDERATIONS

The bridge layout and girder framing plan are typically shown with reference to either a line tangent to the centerline of the bridge or the long chord from abutment to abutment. As mentioned earlier, the maximum and minimum overhang length should be investigated. The maximum overhang length is necessary for the contractors to size the deck forming system. The minimum overhang should cover the top flange of the precast girder and accommodate a drip groove or bead at the edge of the deck slab. A reasonable minimum overhang range is 2 to 6 in. from the edge of the top flange of the girder.

In laying out the geometry of the bridge, the location and length of the overhangs plays an important role in the design. For example, the girder moment on the outside of the curve is dominated by the overhang at the center of the span so this overhang should be optimized when possible. Consideration should also be given to placement of the longitudinal deck steel at expansion joints. In extreme cases, it may be necessary to develop a detailed reinforcement plan to assure proper placement of the distribution steel.

A horizontally curved bridge moves both radially and tangentially due to expansion and contraction. The effect of column stiffness and skew further complicates the orientation of the movements. Substantial skews, which are common in curved bridges, can cause more problems in expansion devices than the effects of the bridge curvature. It is desirable to minimize the use of expansion joints and expansion bearings, if possible, to reduce the potential for problems during the life of the structure.

The design of connections between the superstructure and substructure for forces resulting from curvature and significant skews, when the substructure flexibility can accommodate movements, has proven to be a reliable method of accommodating complex movements in different directions. The use of neoprene pads connecting the girders to the piers with fixed-pinned conditions also represents a good solution that allows the piers to deflect as thermal movements occur. Integral abutments have been used extensively to accommodate bridge movements without bearing devices and to move expansion joints off of the bridge to enhance durability.

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Integral pier caps, where the cap extends into the bridge overhang, can be used to support larger overhangs on the inside of a curve which rapidly decrease as the distance from the pier increases. Since the length of a large overhang is relatively short, little additional reinforcement is needed in these areas.

Reversing superelevations on the bridge can result in problems in areas of freezing weather. The deck is essentially flat at the superelevation transition and will not drain; creating a potential thin layer of water that can freeze. In addition, girders may not be able to follow the roadway grade at superelevation transitions when the beginning or end of the transition is not at the beginning or end of a girder segment. This can result in large or sometimes negative haunches or deck thicknesses. Such situations should be avoided to the extent possible.

Every effort should be made to avoid locating precast girder bridges in a sag vertical curve as this can cause excessive haunch depths at supports.

2.5 FABRICATION, TRANSPORTATION, AND ERECTION

2.5.1 Fabrication Straight girders are easier to produce, handle, transport, and erect compared to horizontally curved girders. However, additional costs are often incurred in the fabrication of straight girders on a curved alignment due to varying lengths. Unique shop drawings and form setups are required for each girder. Also, the girders require plant storage to be organized in such a way to be able to access specific girders for shipment.

2.5.2 Transportation and Erection Curved bridges using straight chorded members have no special transportation or erection issues. That being said, reminders of good transportation and erection practices are worth stating.

Transportation of large precast, prestressed concrete bridge girders requires an experienced trucking company with specialized equipment. The hauling equipment has weight limits that will vary for each location. These limits may affect the design of the precast girders by limiting the total weight of a single piece. Other factors that may limit piece weight are crane capacity and agency load restrictions. Precast girder weight restrictions should be carefully considered during the design phase because they may affect girder lengths, or in the case of spliced- girder construction, segment weights and splice locations.

A detailed erection plan is recommended to provide for the safe, proper, and efficient erection of the bridge structure. The erection plan should include crane locations and mobilizations, temporary shoring and bracing requirements, precast girder segment orientation, erection sequence, and safety plans. The mark number and mark orientation of the erection plan should match the piece marks shown on the precast girder shop drawings. Any required shoring and bracing must be properly designed to ensure the safety of the worksite through the entire construction process.

The precast girder erection plan should be developed simultaneously with the girder shop drawings. This allows for the proper design and location of handling devices, bracing attachment embedments, and safety equipment inserts that must be cast into the precast concrete members. The handling devices are typically composed of multiple loops of prestressing strands. Ideally, girders should be lifted with the crane lines vertical, forming a 90- degree sling angle with the precast girder. Sling angles lower than 90 degrees impart additional load to the lifting devices and the girder so all components must be designed accordingly. All lifting devices should be designed with a factor of safety (FS) equal to four, minimum. All inserts, embedments, and sleeves required for erection bracing or safety equipment must be fully designed and information supplied to the precast concrete manufacturer prior to finalizing the production drawings. During erection, the precast girder segments should be placed so that the girder ends are plumb (unless specified otherwise in the plans) and situated at the proper location in plan.

Local certified precast manufacturers can provide design and detail assistance during the design process. They can provide specific information regarding the fabrication, transportation, and erection phases of the project. These capabilities vary from plant to plant as well as region to region. Therefore, obtaining input from these manufacturers can be important in improving project costs.

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2.6 COST CONSIDERATIONS

The fact that each girder is cast straight with ends set on piers greatly reduces costs and generally results in the most cost-effective solution for this type of bridge construction. However, additional costs may be incurred for precast girders if varying lengths result in different strand patterns between girder lines. Cambers for each girder line may also vary and haunch thicknesses may need to vary between girder lines to ensure accurate final deck elevations.

2.7 PROJECT STUDIES

Two project studies are presented. The first project is the SR 50 Bridge over Happy Hollow Creek in Tennessee. Its substructures have varying skews to allow the girder lengths to be equal in most of the spans. The second project is the PHX Sky Train Guideway Bridge in Phoenix, Ariz. It has radial substructures and parallel girders with unequal lengths within each span.

2.7.1 SR 50 Bridge over Happy Hollow Creek

2.7.1.1 Project Information

Project Name—SR-50 Bridge over Happy Hollow Creek

Location—Tennessee

Owner—Tennessee Department of Transportation

Dates of Letting, Construction, and Completion—

Let to Contact—May 6, 1994

Completed—September 6, 1996

2.7.1.2 Structural System

The nine-span bridge carrying State Route 50 over Happy Hollow Creek in Tennessee, is 1,175 ft long and 46 ft wide (Wasserman, 1999). Span lengths along the centerline of the roadway vary from 129 to 140 ft. Each span consists of six, 72-in.-deep, precast, prestressed concrete AASHTO bulb-tee girders spaced at 7.5-ft. The 8¼-in.- thick composite deck has a 4-degree, 45-minute curve (radius ≈ 1,206 ft) for approximately 976 ft and a spiral curve for the remaining 199 ft. The bridge is designed as simple spans for noncomposite dead loads, and continuous for live loads and composite dead loads. Its deck is jointless and it has integral abutments. An aerial view of the bridge is shown in Figure 2.7.1.2-1. The bridge cross section is shown in Figure 2.7.1.2-2, and its elevation and plan views are shown in Figure 2.7.1.2-3.

Supporting the superstructure are two-column piers that vary in height from 51 ft to 91 ft. These parallel substructures have variable skews to allow all girders in all spans except one to be the same length. Since the girders are chorded, the deck overhang on each side of the bridge varies from 3.5 ft to 5.5 ft along the span length.

The Happy Hollow Creek Bridge contains 6,946 linear ft of girders and 47,000 sq ft of precast, prestressed concrete, partial-depth bridge deck panels.

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Figure 2.7.1.2-1

Aerial View of Happy Hollow Creek Bridge (Photo: Tennessee Department of Transportation)

Figure 2.7.1.2-2

Typical Cross Section—Happy Hollow Creek Bridge (Drawing: Tennessee Department of Transportation)

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Figure 2.7.1.2-3

Elevation and Plan Views of Happy Hollow Creek Bridge (Drawing: Tennessee Department of Transportation)

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2.7.1.3 Construction

Construction of the Happy Hollow Creek Bridge required little in the way of special staging, as access for equipment was available for most of the length of the bridge. The exception to this was the lack of access for erecting girders in the first span. Because of the steep ground in the area of the first span, the girders were erected using a launching truss. For this span, the girders were delivered to the abutment, off-loaded by crane, and lowered so that one end rested on a dolly that ran on tracks atop the launching truss. The other end of the girder was supported by the crane at the abutment. The crane advanced the girder until the leading end could be reached and raised by a crane located near the first interior pier. After both ends were attached to cranes, the girder was moved laterally into place. All girders for the first span were set in this manner.

2.7.1.4 Lessons Learned

The Happy Hollow Creek Bridge was a significant advancement in the design and construction of jointless prestressed concrete bridges. At a length of 1,175 ft, it is the longest jointless, continuous, prestressed girder bridge in the United States. The bridge validates the soundness of the design approach used.

2.7.2 PHX Sky Train™ Guideway Bridge

2.7.2.1 Project Information

Project Name—PHX Sky Train Elevated Guideway

Location—Sky Harbor Airport, Phoenix, Ariz.

Owner—City of Phoenix, Ariz.

Dates of Letting, Construction and Completion—

Bid Date—August 6, 2009

Start Date—February 9, 2010

Completion—October 19, 2010

2.7.2.2 Structural System

The guideway transports airport passengers from the long-term parking facilities to the main terminal at Sky Harbor Airport in Phoenix, Ariz. (Burrows, 2011). It consists of 130 pieces of 5-ft-deep pretensioned trapezoidal U-girders ranging in span length from 58 ft to 100 ft. The maximum girder weight was 72 tons, which included the plant-cast integral diaphragms. The precast portion of the structure is made up of 39 spans with girder quantities varying from one to five girders in each span depending on the track geometry and station requirements. An elevation view of the bridge is shown in Figure 2.7.2.2-1. The bridge cross section is shown in Figure 2.7.2.2-2, and a partial plan view is shown in Figure 2.7.2.2-3.

Figure 2.7.2.2-1

Elevation View of PHX Sky Train Guideway (Photo: Hensel Phelps Construction Co.)

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Figure 2.7.2.2-2

PHX Sky Train Guideway Cross Section (Drawing: Gannett Fleming)

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Figure 2.7.2.2-3

Partial Plan View of U-Girder Layout—PHX Sky Train Guideway (Drawing: Gannett Fleming)

2.7.2.3 Construction

The guideway consists of precast, prestressed girders, steel girders, and cast-in-place segmental girders. Of these three methods, the precast option was selected in the heavily traveled corridor adjacent to the terminal. Aesthetics and the elimination of falsework were key factors in this decision. Girder erection took place in the

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evenings between the hours of 10 P.M. and 5 A.M. when airport traffic was minimal. An 8-in.-thick cast-in-place concrete deck was placed on the girders using stay-in-place metal decking to complete the superstructure. To accommodate the vertical geometry of the guideway, embedded plates were cast in the bottom of the U-girders. Beveled sole plates were welded to the embedded plates to provide a horizontal bearing surface for the elastomeric bearing pads.

2.7.2.4 Lessons Learned

The U-girder is an aesthetically pleasing shape that can be adapted to curved profiles in both the vertical and horizontal directions. Girder weights have a significant impact on field installation. Particular attention should be given to minimizing web and soffit thicknesses, along with consideration given to casting intermediate diaphragms at the jobsite after the girders are in place in the structure.

3.0 STRAIGHT GIRDER SEGMENTS WITH SPLICES WITHIN THE SPANS

3.1 INTRODUCTION AND BACKGROUND

Bridges with curved alignments and complex roadway geometry can be constructed using a series of straight precast concrete girders that are “kinked” at locations within each span. This approach can easily be accomplished using spliced girder construction where a change in direction is introduced at the splices between the girders to allow them to more closely follow a curved alignment. There are several but yet relatively few examples of spliced precast girder construction used in this manner to accommodate curved alignments. One notable example is shown in Figure 3.1-1. The most common application of precast concrete bridges to curved alignments has been to simply chord from pier to pier as described in Chapter 2. Spliced construction, to date, has been successfully used for straight long-span projects. The projects where this technology has been used to accommodate complex curved roadway geometry have also been extremely successful.

Figure 3.1-1

Rosebank Pataki Bridge during Construction (Photo: Beca, Carter, Hollings, and Ferner Ltd.)

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Spliced girder construction creates the opportunity for multiple angular breaks in each span, which makes it geometrically possible to accommodate longer spans and sharper horizontal curvatures. By increasing the number of girders and as a result increasing the number of angle breaks between girders within a particular span, the offsets of the straight girders from the curved deck alignment can be greatly reduced, making longer spans and tighter curves more feasible for precast construction using straight girders. Figure 3.1-2 shows the Rosebank Pataki Bridge in New Zealand that accommodates a 500-ft radius with a straight girder framing plan that includes splices within the span (Powell and Snoep, 1998). The continuous post-tensioned structure used straight girders that were “kinked” at the splices to follow the tightly curved alignment. Using precast construction for this project provided a more economical bridge solution when compared to other conventional methods.

Figure 3.1-2

Partial Framing Plan—Rosebank Pataki Bridge (Drawing: Beca, Carter, Hollings, and Ferner Ltd.)

Spliced girder construction has enormous potential to expand the use of precast concrete in the construction of urban interchanges, overpasses, and viaduct bridges with complex roadway geometry constraints that require longer spans and tighter horizontal curvatures.

3.2 AESTHETICS

Spliced girder construction can greatly improve the visual attractiveness of a curved structure as shown in the completed Rosebank Pataki Bridge in Figure 3.2-1. The number and location of splices within each span can be designed to enhance the structural efficiency, constructability, and aesthetic appeal of a structure by more closely simulating the curved alignment while using straight sections.

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Figure 3.2-1

Completed Rosebank Pataki Bridge (Photo: Beca, Carter, Hollings, and Ferner Ltd.)

In spliced girder construction, the length of each straight girder segment is shorter than the length of the span. The resulting offsets are greatly reduced from a typical pier-to-pier straight girder chord. The primary benefit is to simulate the appearance of a curved girder and to reduce the variation in the length of the overhangs and the resulting shadow lines. As the ratio of the length of each straight girder segment relative to the radius of curvature becomes smaller, the variation in the overhangs is greatly reduced and the overall appearance approaches one of a curved girder.

The Philadelphia Airport Bridge (Barnoff et al., 1984) is an example of a curved girder bridge and is described in Chapter 4. It used precast concrete girders that were cast in 20-ft-long straight segments that were assembled in the fabrication plant to simulate a curve on an extremely short radius. Curved segmental bridges actually consist of numerous short straight segments that are match-cast along the horizontal alignment. The result is a structure that appears as a curved box girder. A curved bridge using straight segments of precast concrete trapezoidal box girders with angular deviations at splice points is shown in Figure 3.2-2.

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Figure 3.2-2

Bijou Street Bridge in Colorado Springs, Colo.

Spliced girder construction of curved bridges using straight sections is effective for a range of situations that often use more conventional design alternatives such as steel or cast-in-place concrete construction. The Rosebank Pataki Bridge in New Zealand is an excellent example of how spliced girder construction can use conventional straight girder segments in a creative manner to produce an attractive solution to a complicated intersection project with short radii and difficult traffic maintenance considerations.

3.3 DESIGN AND ANALYSIS CONSIDERATIONS

Spliced precast concrete bridges are typically post-tensioned structures that are designed for longer spans that cannot be accommodated by conventional pier-to-pier construction. Whether straight or curved, these structures require temporary support of the precast concrete girders during construction. Figure 3.3-1 shows a relatively short pier segment stabilized by shores resting on the pier footing. The drop-in spliced girder segments are supported from the pier segment by temporary steel hangers or strongbacks. In some construction, shores are placed under the splices. Site conditions must be carefully considered early in the design process to determine where locations for temporary supports are possible. Once this issue is resolved, the design of these structures must consider a number of conditions including existing facilities and traffic patterns, aesthetics, and future needs.

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Figure 3.3-1

Temporary Shores and Hangers Support Precast Segments during Construction on the Rosebank Pataki Bridge

(Photo: Beca, Carter, Hollings, and Ferner Ltd.)

In general, only vertical shoring and sometimes hangers are required to support precast girders. Once the girders are erected and supported on temporary shoring, they can span over traffic openings with minimal disruption, which reduces the need for traffic control. Temporary shoring that consists primarily of a few vertical supports requires a smaller footprint than what is required for cast-in-place concrete construction. Once shoring is in place, precast girder erection is typically straight forward. In Figure 3.3-2, a curved bridge is framed with end girder segments that cantilever over the pier shown. Center span girder segments are hung from the cantilevered girders using temporary steel strongbacks. The angular deviation is made at the splice.

Figure 3.3-2

Temporary Hangers Used in a Curved, Spliced, U-Girder Bridge during Construction

Once the site conditions have been evaluated in the design phase and the suitability of using shored construction has been determined, the design process is similar for both straight and curved continuous, post-tensioned concrete bridges with the exception of the three-dimensional aspects of curvature on the structural system. To

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properly analyze and evaluate these bridges, a combination of two- and three-dimensional analyses is appropriate. Additional design considerations that must be evaluated for curved and complex urban construction include:

 Geometric constraints of roadway geometry

 Lateral loadings due to post-tensioning

 Curvature effects on the structural system

The majority of procedures and practices for the design and construction of spliced, post-tensioned concrete bridges have been covered in detail in other references such as PCI, 2011; Castrodale and White, 2004; PTI, 2003; and PTI, 2006. The following sections will focus on those aspects of design and analysis that are particular to curved construction.

3.3.1 Geometric Constraints Figure 3.3.1-1 illustrates two curved precast concrete bridges that are designed to accommodate a curved alignment. Both bridges have the same overall length and curvature. Both bridges have the same number of straight girders that are all the same length. The girders are set around the horizontal alignment in the same manner with the same maximum offsets from the curved alignment at the midspan on the outside of the curve and at the piers on the inside of the curve. The two configurations differ in span lengths and number of piers.

Figure 3.3.1-1

Comparison of Framing Plans for Spliced Girder and Simple-Span Bridges

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The conventional bridge layout in Figure 3.3.1-1 has girders spanning from pier to pier, a series of uniform spans of length “L” and six piers. The spliced girder layout has four piers and spans that vary from 1.5 to 2.0 times the basic length, L, of the conventional layout. The impact on construction cost of a spliced girder layout requiring temporary support having small foundations versus the simpler construction of a conventional layout are subjective and cannot be properly evaluated in this report. The important point to recognize is that the spliced girder system has the ability to accommodate existing or future site conditions that require longer spans and fewer substructures without affecting the geometry of the superstructure.

In addition, spliced girder construction increases the applicability of using straight girders to more sharply curved alignments that would be impractical with a conventional pier-to-pier framing plan. In Chapter 2, it was pointed out that straight girder bridges on sharply curved alignments can result in poor appearance and reduced structural efficiency, and at some point become impractical. Figure 3.3.1-2 shows the relationship of the chord length of a straight girder to the corresponding offset for a range of chord lengths across different radii. By establishing acceptable offsets early in the design process, the feasibility of using straight girder sections can be easily determined for a range of curvatures and span and girder lengths.

Figure 3.3.1-2

Straight Girder Offsets from Horizontally Curved Alignments

Spliced girder construction establishes the opportunity for multiple angular changes within each span. By introducing more angle breaks and reducing the length of each straight girder relative to a curved span or the overall bridge length, the resulting offsets from the curved alignment can be greatly reduced. The smaller offsets make longer spans and sharper curves more feasible with little or no impact to the aesthetics or structural performance of the bridge.

Interchange bridges in urban areas must respond to a variety of roadway design conditions such as on- and off- ramps, gore areas, skewed foundations, and variations of the overall deck width. The I-70 Viaduct over Washington Street in Denver, Colo., shown in Figure 3.3.1-3, is an example of spliced I-girder construction that accommodates a five-lane viaduct with a mainline and exit ramp with a 1,700-ft radius curved alignment having skewed piers and abutments. The framing plan for the bridge, which spans over the Platte River and Washington Street, consists of 11 continuous lines of spliced bulb-tee girders with kinked splices up to 2.7 degrees with transverse diaphragms that accommodate a deck slab that varies in width from 96 to 113.5 ft.

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Figure 3.3.1-3

Framing Plan for the I-70 Viaduct over Washington Street in Denver, Colo. (Drawing: Jacobs (Carter & Burgess))

The Bijou Street Bridge, shown in Figure 3.3.1-4 (Reese, 2009), is another example of a bridge in an urban environment on a gradual curve with a spliced girder framing plan that responds to complex roadway design conditions. The bridge accommodates on- and off-ramps to an adjacent interstate highway and spans over a creek and railroad yard while funneling traffic into a congested downtown area. The framing plan consists of seven continuous lines of spliced precast U-girders. The splices are kinked, in some cases to 4.5 degrees, to accommodate the overall deck layout. Conventional span-to-span construction was evaluated early in the design process and was determined to not be suitable for this application due to the limited structural depth over the railroad yard.

Figure 3.3.1-4

Framing Plan for the Bijou Street Bridge in Colorado Springs, Colo.

Both of these projects demonstrate how creative use of straight precast concrete girders can be used in longer- span urban applications for bridges with complex geometric design conditions.

3.3.2 Lateral Loadings Due to Post-Tensioning The horizontal deviation of the longitudinal post-tensioning at the kinked splices creates a design condition that is particular to curved post-tensioned construction. When straight girders are kinked at splices, the lateral forces are resolved locally in the spliced area as shown in Figure 3.3.2-1.

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Figure 3.3.2-1

Lateral Loads from Post-Tensioning at Girder Splices

The effects of these lateral loadings and the out-of-plane forces that they generate in the girder lines can become significant as the deviation angle β increases due to a combination of longer girder sections and sharper horizontal curvature. In addition, the location of the post-tensioning force varies along the longitudinal tendon profile. The lateral forces generate torsional moments in the girder lines as well when the vertical location of the force is eccentric to the center of gravity of the cross section. A three-dimensional analysis as shown in Figure 3.3.2-2 is an appropriate method to evaluate the magnitude of these load effects.

Figure 3.3.2-2

Analysis of Lateral Post-Tensioning Loads on a Three-Span Curved Bridge

The out-of-plane forces that are generated by the lateral loads at the splice locations can be significant in slender girder sections. These loads can be globally resisted by the framing system by placing transverse diaphragms between the girder lines at the kinked splices as shown in Figure 3.3.2-3. If the post-tensioning is stressed into the composite section, these forces are also resisted by the deck slab.

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Figure 3.3.2-3

Transverse Diaphragms at Kinked Splices in the I-70 Washington Street Bridge

The longitudinal post-tensioning is typically routed through the girder webs. These webs are relatively thin and can be particularly vulnerable to local spalling from lateral forces that can pull the post-tensioning duct from the side of the web. In addition, misalignments during erection can multiply the lateral loads at these locations. A thickened cross section or end blocks at girder splices have been used to provide greater resistance to local pullout forces. Transverse diaphragms are also an effective way to resist the local effects of lateral post-tensioning forces.

The length of splices between girders should allow an adequate bend radius in the post-tensioning ducts to laterally deviate the post-tensioning tendons in a smooth arc. Deviation angles less than approximately 5 degrees can be accommodated with field-bent conventional ductwork. Larger deviation angles may require a fabricated deviation pipe to avoid kinks in the post-tensioning tendons and to reduce the possibility of wire breakage or fretting fatigue.

3.3.3 Loadings Due to Curvature Curved construction introduces the opportunity for torsional loadings and differential loading on girder lines from the inside to the outside of a curved span. The differential loading on the inside and outside of the curve should be considered in separate analysis and evaluation of each girder line to determine if these load effects are significant. A three-dimensional analysis of the framing plan, as shown in Figure 3.3.3-1, can be used to determine the variation of load effects in each girder line and evaluate whether a simplified design that is based on the longer outside girder line is appropriate or if more detailed analysis is necessary.

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Figure 3.3.3-1

Gravity Load Moments in a Three-Span Curved Bridge

The geometry of curved bridges also produces torsional moments in each girder line. The magnitude of torsion may be significant in sharply curved bridges with longer spans or bridges with slender cross sections, such as bulb-tee girders and I-girders. The torsion carried by the girder cross section can be significantly reduced by placing transverse diaphragms at girder splices. Figure 3.3.3-2 shows the torsional moments that occur in a three- span spliced girder bridge with diaphragms at kinked girder splices.

Figure 3.3.3-2

Gravity Load Torsional Moments in a Three-Span Curved Bridge

The transverse diaphragms resolve a significant portion of the local torsion on each girder line into the global framing system that is resolved into differential vertical loadings. Box girders and U-girder sections that become closed sections during construction are more able to resist torsion without the need for transverse diaphragms at splices.

Transverse diaphragms may still be desirable in bridges using torsionally stiff cross sections to resolve lateral tendon forces and prevent bursting of ducts from the girder webs. Figures 3.4-4 and 3.4-5 show the transverse diaphragms that were cast at one splice location in the Bijou Street Bridge, which consists of precast concrete U- girders. These diaphragms strengthen the girder webs against lateral loadings from horizontal deviations in the longitudinal post-tensioning. The girder design was not affected by the introduction of the diaphragms, which were added to prevent local bursting of longitudinal tendons due to significant lateral deviation angles in the kinked splices.

3.3.4 Summary of Design and Analysis The design of curved bridges poses a unique set of design conditions that must be considered. Once these design conditions are evaluated and addressed, the design does not vary greatly from the design of straight spliced- girder bridges. Proper consideration of local conditions that arise from lateral loadings due to post-tensioning around a curve and the development of adequate details can result in structures that perform very well. When using straight sections chorded across a curved alignment, proper appreciation and evaluation of the impact of the offset of straight sections can result in an efficient aesthetically pleasing solution to variable site conditions, longer spans, and increasingly sharp curvatures before a fully curved solution is warranted.

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3.4 DETAILS

The design of curved bridges using straight precast girders that are cast in conventional pretensioning beds and spliced together during construction can be an efficient, cost-effective solution to complex curved bridge construction with longer spans and moderate curvatures. The superstructure is designed to accommodate construction loadings with conventional pretensioning. Continuous post-tensioning is designed for negative and positive moments in the final condition as shown in Figure 3.4-1. This type of design blends details from more conventional pier-to-pier construction as described in Chapter 2, with a framing geometry that can follow a horizontally curved alignment by placing kinks between the girder ends at splice locations.

Figure 3.4-1

Longitudinal Post-Tensioning Layout for a Spliced Precast Concrete Girder Bridge (Drawing: Jacobs (Carter &

Burgess))

The detailing of these structures must consider the placement of post-tensioning tendons within the precast girders and accommodate the lateral forces generated by horizontal deviation of the tendons at the kinked splices. Precast concrete, post-tensioned, continuous structures are typically designed such that some segments resist the negative moments at the interior supports while other segments resist the positive moments at midspan regions, as shown in Figure 3.4-2.

Figure 3.4-2

Pier and Drop-In Precast Girder Segment Details

The positive moment segments, often referred to as drop-in segments, are very similar to typical precast concrete girders and rarely require special detailing. The negative moment segments, also known as pier segments, may require special forming to accommodate structural design requirements. A negative moment region requires a compression block at the bottom of the girder. The girder may need a thickened bottom flange to provide the compression block as is shown in Figure 3.4-2. Variable-depth girders may also be used when the demand on the structure exceeds the flexural capacity that can be supplied with a constant-depth section.

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Because the precast girder segments are straight, the girders can be pretensioned. The pretensioning may be designed to resist only the concrete stresses in the segment during handling, storage, transportation, and erection. However, pretensioning may also be designed to contribute to resisting the external loadings. The longitudinal post-tensioning usually provides the primary longitudinal reinforcement. The tendons are typically placed in the girder webs in a parabolic profile and are anchored either in precast end blocks in the girders or in a cast-in-place concrete diaphragm as shown in Figure 3.4-3.

Figure 3.4-3

Longitudinal Post-Tensioning Anchorages Placed in an Abutment Diaphragm

Figure 3.4-4

Plan and Section Views of a Transverse Diaphragm at Kinked Splices in the Bijou Street Bridge

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Figure 3.4-5

Transverse Diaphragm at a Kinked Splice in the Bijou Street Bridge

The longitudinal post-tensioning ducts are connected together at the girder splices. Kinks between the girders at the splice locations concentrate the horizontal angle change in the longitudinal post-tensioning at the splices and produce local concentrated lateral loads that make the girders and spliced sections vulnerable to lateral bursting or spalling. Transverse diaphragms are often used to resist these loads as shown in Figures 3.4-4 and 3.4-5. Misalignments between the girders on either side of the splice may further magnify these lateral loads. Girder splices should be conservatively designed and detailed to provide adequate confinement reinforcement to prevent distress. The length and geometry of the spliced section should be considered in design to provide adequate space to distribute the tendon angle changes in a smooth curve and properly develop the confinement reinforcement. Figure 3.4-6 shows an example of reinforcement at the ends of U-girders at a splice.

Figure 3.4-6

Kinked Splice Reinforcement Details at the Ends of Precast U-Girders

Design details must resolve both the local effect of lateral loads in each girder line and at each splice location, as well as the global effects on the framing. Bridges with laterally slender girders typically require transverse diaphragms to resolve these lateral loads as shown in Figure 3.4-7. Bridges with stiffer cross sections, such as U- girders or box girders, may not require diaphragms and can be designed with a thickened section at the splice with lateral confinement reinforcement as shown in Figure 3.4-6. The post-tensioning ducts must be carefully

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sealed in the splices to prevent concrete intrusion during casting of the closures and also to prevent leakage during grouting after the tendons are stressed.

Lateral loads at the kinks will also generate transverse flexure in the girder lines that should be considered in the design. This effect is not generally significant unless the angle breaks are large or the framing plan does not include transverse diaphragms with slender girders. Lateral loads generated by the post-tensioning at kinked splices must also be resisted by the foundations when the girders are laterally restrained at the piers and abutments. These loads are not usually large but should be considered during design of the substructure.

Figure 3.4-7

Transverse Diaphragms at Kinked Splices of I-Girders (Photo: Jacobs (Carter & Burgess))

3.5 FABRICATION, TRANSPORTATION, AND ERECTION

3.5.1 Fabrication Post-tensioned construction poses a unique set of challenges related to precast girder fabrication. The continuity of the superstructure requires special detailing for the precast members to accommodate both negative and positive moments. A major part of the detailing required for the precast segments involves the layout of post- tensioning ducts. Typically, the post-tensioning subcontractor has the responsibility for finalizing the duct layout based on the tendon information provided in the contract plans. This requires coordination between the precast supplier and post-tensioning subcontractor to ensure the correct duct layout is shown on the precast girder shop drawings. Additionally, special fabrication for duct splices, anchorage blockouts, anchorage reinforcement, splice reinforcement, etc., as mentioned in the previous section, must be coordinated and shown on the precast girder shop drawings. These designs may also require special forms and fabrication procedures.

Pretensioning strand in the bottom of the straight girder sections can be used to provide additional positive moment capacity and add resistance to help control concrete stresses. Similarly, pretensioned strand can be provided in the top of the precast segments to provide additional resistance to concrete stresses caused by negative moments. For the purpose of production efficiency, the number of different strand patterns should be kept to a minimum to allow multiple pieces to be produced in the same casting line.

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3.5.2 Transportation Curved bridges designed with spliced straight girders have only a few special transportation or erection issues beyond what was presented in Chapter 2. Transportation of the girders into congested construction sites must be considered when developing an erection plan. Modifications to temporary shoring may be required to accommodate crane capacities and trucking requirements. Precast girder segment weight restrictions and access for lifting equipment should be carefully considered during the design process because these may affect segment lengths and splice locations. As started in Chapter 2, a detailed erection plan is essential for the safe, proper, and efficient erection of the bridge structure. Coordination between the designer and the construction community prior to bid can greatly enhance the constructability and economy of the project.

3.5.3 Erection Shoring towers that provide temporary support for the girders during construction are typically placed at splice locations until the girder lines are post-tensioned and self supporting. Temporary supports that are erected near existing traffic must be designed to withstand vehicle crash impact loads or be a sufficient distance behind barriers. Strongbacks, supported from cantilevered ends of abutting girders, have also been used to support the ends of drop-in girders. This reduces the need for additional shoring and reduces the impact on the construction site.

While spliced girder erection is more complex than typical pier-to-pier erection, it generally requires only vertical supports and small platforms to provide construction access to cast girder splices and install post-tensioning. The girders span between temporary supports and the permanent substructure which minimizes setup and dismantling costs during construction.

The Bijou Street Bridge in Colorado Springs, Colo. (Reese, 2009), was erected over Monument Creek and the UPRR rail yard using only strongbacks and no vertical shoring. The strongbacks were attached to the ends of girders that cantilevered 15 ft beyond each interior pier. The ends of adjacent girders were supported from the strongbacks with high strength, post-tensioning bars as shown in Figure 3.3-2.

Temporary supports and other special erection assemblies are engineered to resist gravity, wind, and construction loads but are usually not affected by the bridge curvature because each member is straight.

3.5.3.1 Requirement for Licensed Construction Engineer

It is recommended that project specifications require a licensed engineer be an active participant in the curved bridge girder construction. The engineer must be familiar with bridges using spliced girder construction that requires temporary support during construction, the design of temporary structures, heavy load erection, and the use of post-tensioning systems.

3.6 COST CONSIDERATIONS

Spliced girder construction with straight precast members is a cost-effective way to build curved bridges when design considerations such as degree of curvature, span length, and aesthetics are considered. The cost of precasting, erecting, and post-tensioning this type of structure is generally more expensive than comparable bridges where girders are set from pier to pier as described in Chapter 2. Spliced girder construction utilizing continuity makes longer spans possible using similar-sized precast elements. This reduces the number of piers and potentially the cost of the substructure and creates more flexibility in span arrangements, which may enable the designer to take advantage of continuity and potentially eliminate a girder line.

Precasting girders for continuous spliced applications is more expensive for each piece, primarily due to the added complexity of adding post-tensioning ducts and possibly anchor blocks. As stated, greater efficiency of the designs of both the substructure and superstructure may offset the additional cost of precasting, post-tensioning, providing temporary supports, and casting splices during construction. All of these cost factors are related to spliced girder construction and are not particularly sensitive to whether the bridge is curved or straight.

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3.7 PROJECT STUDIES

Three case studies are presented here. Each is a precast girder bridge constructed with spliced, straight precast members, kinked at each splice to follow a curved horizontal alignment. These bridges utilize spliced, continuous, post-tensioned construction to accomplish various design constraints to produce an economical precast concrete girder-and-slab solution. A brief discussion of the three representative projects is presented in the order of their construction.

3.7.1 Rosebank Pataki Interchange Bridges

3.7.1.1 Project Information

Project Name—Rosebank Pataki Interchange Bridges

Location—Auckland, New Zealand

Owner—Transit New Zealand

Dates of Letting, Construction and Completion—August 1996 to December 1997

3.7.1.2 Structural System

The Rosebank Pataki Interchange located in Auckland, New Zealand, was constructed to relieve congestion on an at-grade interchange (Powell and Snoep, 1998). The interchange consists of three curved bridges, two of which are curved flyover ramps. The curved ramps have a main span that crosses the main motorway as shown in Figure 3.7.1.2-1. The ramps were sharply curved and required spans in excess of what could be prefabricated and transported; this led to a spliced precast girder solution.

Figure 3.7.1.2-1

Plan View of Ramps A and B, Rosebank Pataki Interchange (Drawing: Beca, Carter, Hollings, and Ferner Ltd.)

Of the three bridges, the Ramp B Bridge is one of the most prominent examples of what can be accomplished using spliced straight girder construction. The bridge has four spans, from 107 ft up to a 138-ft-long main span on a 500-ft radius that consists of 71-in.-deep straight precast I-girders that are kinked at the quarter points of the span to follow the curved alignment.

All of the bridges were constructed in 1997 and 1998. Ramp B is a 950-ft-long structure consisting of two independent units. A 518-ft-long approach unit of six simple spans with three lines of precast concrete girders on a slightly curved alignment joins a four-span continuous, post-tensioned unit of three lines of spliced precast I-

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girders that were kinked at the splices to accommodate a very sharp radius. The continuous girder unit was constructed on falsework with integral bents on either side of the Northwestern Motorway. The splices were located to segment the horizontal curve and enhance the completed structure aesthetics while not encroaching on the existing traffic. The resulting structure is an excellent example of what can be constructed with innovative applications of precast concrete to challenging design constraints. Figure 3.7.1.2-2 shows the Ramp B framing plan and erection schematics, and Figure 3.7.1.2-3 is a completed aerial view of Ramp B.

Figure 3.7.1.2-2

Layout and Construction Sequence of Ramp B Girder Segments in Roadway Overcrossing (Drawing: Beca, Carter,

Hollings, and Ferner Ltd.)

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Figure 3.7.1.2-3

Aerial View of Completed Ramp B, Rosebank Pataki Interchange (Photo: Beca, Carter, Hollings, and Ferner Ltd.)

3.7.1.3 Construction

The project used a framing system of straight precast concrete I-girders that were spliced within the span and post-tensioned for continuity. The girders were kinked at the splices to follow the horizontal alignment of the bridge. Girder lines were connected with transverse concrete diaphragms at girder splices and at the piers and abutments. Girders were supported with temporary shoring during construction, and girders spanned over existing traffic openings.

3.7.1.4 Lessons Learned

Spliced precast girder construction was selected as the most cost-effective solution after a detailed bridge type study was performed. The system worked well and resulted in a project that not only met the project requirements but was constructed within the budget and project schedule with minimal disruption to traffic. The project demonstrated that spliced precast girder construction can be successfully used for projects with sharply curved alignments in congested urban areas.

3.7.2 I-70 Elevated Viaduct over Washington Street and BNSF Railroad

3.7.2.1 Project Information

Project Name—I-70 Over Washington Street and the BNSF Railroad

Location—Denver, Colo.

Owner—Colorado Department of Transportation

Dates of Letting, Construction and Completion—1997 to 1999

3.7.2.2 Structural System

The I-70 Viaduct in Denver, Colo., is an example of how precast spliced girder construction can be used to build an elevated freeway that accommodates complex urban roadway design constraints with curved alignments, gore areas, skewed foundations, and variable deck widths. The project consists of two sections of elevated bridges, the

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I-70 Bridge over Washington Street and the Platte River and the I-70 Bridge over 46th Avenue and the BNSF Railroad. Both bridges have framing plans that consist of continuous lines of precast concrete straight spliced girders that are post-tensioned and kinked at the splices to match the slightly curved transitioning roadway geometry as shown in Figures 3.7.2.2-1 and 3.7.2.2-2.

Figure 3.7.2.2-1

Framing Plan, I-70 Viaduct over Washington Street and the Platte River (Drawing: Jacobs (Carter & Burgess))

Figure 3.7.2.2-2

Framing Plan, I-70 Viaduct over 46th Avenue and the BNSF Railroad (Drawing: Jacobs (Carter & Burgess))

The Washington Street Bridge is a four-span unit that is 630 ft long with spans that vary from 105 to 174 ft. The deck varies in width from 93 to 110 ft and is supported on 11 continuous girder lines as shown in Figure 3.7.2.2- 3. Each girder line consists of seven girder segments that are spliced at the quarter point of each span on either side of the interior piers. The end span and drop-in girders are 84-in.-deep modified bulb-tee girders. The pier girders are haunched to a maximum depth of 108 in. at the piers, as shown in Figure 3.7.2.2-4.

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Figure 3.7.2.2-3

I-70 Viaduct over Washington Street During Construction. The Cantilevered, Haunched Pier Segments are Shown in

the Foreground. (Photo: Jacobs (Carter & Burgess))

Figure 3.7.2.2-4

Typical Haunched Girder Cross Sections, I-70 Viaduct Bridges (Drawing: Jacobs (Carter & Burgess))

The 46th Avenue and BNSF bridge consists of three units and is 1,875 ft long with spans that vary from 105 to 188 ft. Units 1 and 2 each have three spans and are spliced and post-tensioned with the same cross sections as the Washington Street bridge. The third unit is a pier-to-pier, simple-span continuous unit with no longitudinal post- tensioning.

Both bridges were supported during construction using a combination of temporary shoring and strongbacks.

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3.7.2.3 Construction

The project used a framing system of straight precast concrete bulb-tee girders that were spliced within the span and post-tensioned for continuity. The girders were kinked at the splices to follow the horizontal alignment of the bridge. Girder lines were connected with transverse concrete diaphragms at girder splices and at the piers and abutments. Girders were supported with temporary shoring and strongback hangers during construction and girders spanned over existing traffic openings.

3.7.2.4 Lessons Learned

The I-70 project demonstrates that spliced precast girder construction can be used for urban viaduct construction with varying roadway design conditions requiring variable deck widths, gore areas, and adjacent ramp structures. Spliced girder construction accommodated the longer spans required over traffic crossings, a rail yard, and a river, while producing a unified structural solution for an urban viaduct constructed in multiple phases by different contractors.

3.7.3 Bijou Street over Monument Creek

3.7.3.1 Project Information

Project Name—Bijou Street Bridge

Location—Colorado Springs, Colo.

Owner—City of Colorado Springs, Colo.

Dates of Letting, Construction and Completion—January 2007 to November 2007

3.7.3.2 Structural System

The Bijou Street Bridge is a gateway structure that connects downtown Colorado Springs, Colo., with I-25 and the western part of the city (Reese, 2009). The bridge was constructed as part of a design-build project to widen I-25 through Colorado Springs. The bridge replaced a deteriorated structure that was built in sections between 1921 and 1965. The new bridge accommodates a complex roadway design that includes on- and off-ramps from I-25, left turn lanes, and a constricted opening in the downtown area. The bridge crosses over Monument Creek and the Union Pacific/BNSF Railroad yard as shown in Figure 3.7.3.2-1.

Figure 3.7.3.2-1

Completed Bijou Street Bridge (Photo: Precast/Prestressed Concrete Institute)

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The roadway varies from 88 to 178 ft and has a horizontal alignment with a 2000-ft radius center curve. The grades on either side of the vertical alignment were kept to a minimum to increase the distance which severely limited the available structural depth over the rail yard. A structural depth of 6 ft was available to accommodate a 148.5-ft-long main span over the rail yard. The framing system consists of seven continuous 60-in.-deep precast U-girders that were spliced and post-tensioned. The girder spacing varies from 13 to 23 ft and supports a cast-in- place concrete deck.

The bridge was slightly curved but the extreme variation of the bridge width along its length required that the girders be kinked at the splices as shown in Figure 3.7.3.2-2. The kink angles varied between each girder line from 0 to 4.5 degrees at any single splice location.

Figure 3.7.3.2-2

Kinks at Splices in the Bijou Street Bridge

3.7.3.3 Construction

The project used a framing system consisting of seven continuous lines of straight precast concrete U-girders that were spliced within the span and post-tensioned for continuity. The girders were kinked at the splices to follow the horizontal alignment and varying width of the bridge deck. An innovative construction scheme had the girders erected from each abutment toward the railroad span and cantilevering over the head pier to support the end of the adjacent girder from strongbacks. This system reduced erection stresses and deflections in the relatively shallow girders and eliminated the need for any ground-based shoring during construction while spanning over a creek and a rail yard. The bridge was constructed in less than 10 months including demolition, 1 month ahead of schedule. The Bijou Street Bridge demonstrates that spliced-girder, post-tensioned construction with straight precast members can be used to economically construct an attractive structure with a complex set of geometric design conditions.

3.7.3.4 Lessons Learned

The Bijou Street Bridge was constructed as part of a design-build project that involved close cooperation between the design engineer, contractor, and precast manufacturer. The bridge was constructed within budget and ahead of schedule by incorporating the fabricator’s available forming system and the contractor’s means and methods in design. The erection methods, developed by the contractor and engineer, increased the efficiency of the framing system while reducing the overall depth of the final structure and the impact of construction on the site conditions, resulting in no interruption to rail traffic during construction.

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4.0 CURVED GIRDERS

4.1 INTRODUCTION AND BACKGROUND

The use of precast concrete, horizontally curved bridge elements is not new to the industry. A curved monorail guideway at Disneyland was built in the late 1960s and several similar projects followed in the 1970s and 1980s. These ground-breaking projects were followed by the Philadelphia, Pa., airport ramp bridge, designed and constructed in 1983. This bridge was the first application of curved precast concrete girders for roadway bridges. It won the 1985 PCI Harry H. Edwards Industry Advancement Award that identifies “…ideas and concepts that hold the potential to move the precast and prestressed concrete industry to the next generation of technology.”

There are two additional publications related to curved girders. In 1988, PCI published a report on the concept, analysis and design procedures, design alternatives, and fabrication techniques recommended for horizontally curved precast concrete girders to construct curved bridges (ABAM, 1988). This report describes a complete design for horizontally curved girders utilizing closed sections with 5-in.-thick webs and top and bottom flanges. The girders are plant assembled from 20-ft-long chorded segments and use external post-tensioning (inside the box girder, but external to the concrete cross section). The second publication is Chapter 12 of the PCI Bridge Design Manual—Skewed and Curved Bridges. It provides a good overview of curved bridge configurations, curved girder preliminary design, and structural behavior of curved-girder bridges (PCI, 2011—Sects. 12.3, 12.4, and 12.5).

While the use of curved precast concrete girders was successful in each of these applications, the technology has not been widely accepted as an economic alternate to steel or cast-in-place concrete construction in the United States. Following the Philadelphia Airport Bridge, only two roadway bridges were designed and built using curved precast girder construction between 1983 and 2005. The Park Avenue Bridge in Denver was built in 1995 and won the 1999 PCI Design Award for long span bridges (PCI Design Award, 1999; McMullen et al., 2008) In 2004, the Arbor Road Bridge was designed and built in Lancaster County, Neb., and won the 2006 PCI Design Award for medium span bridges (PCI Design Award, 2006).

Between 2005 and 2010, seven different bridge projects were designed and constructed in Colorado using plant manufactured curved precast concrete members with standard Colorado Department of Transportation (CDOT) U-girder cross sections. Several projects, along with CDOT objectives are described in McMullen et al. 2008. This more widespread use of curved precast concrete construction in a defined geographical location with standardized sections has greatly enhanced the economy of the technology. Each project was constructed in a highly urban environment with curved members supported on modest amounts of temporary shoring (Shutt, 2010). This construction method enabled the owner to minimize traffic and construction impacts on the travelling public during construction.

4.2 AESTHETICS

Continuously-curved precast concrete U-girders allow a unified appearance throughout the project at an economical cost. They provide an aesthetically appealing superstructure that uniformly follows the curvature of the roadway. This type of construction is most appropriate in highly visible locations because of its clean lines, non-varying bridge overhangs, and ability to span greater lengths, as shown in Figure 4.2-1. Span lengths can be extended by splicing girders at the site or by providing deeper or haunched sections at the piers to provide a slender span-to-depth ratio that enhances the visual appeal. Haunched sections can also be designed to create a parabolic profile or to simulate the effect of an arch within the spans of the completed bridge.

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Figure 4.2-1

Views of SH 58 Ramp A over I-70 in Golden, Colo.

4.3 DESIGN AND ANALYSIS CONSIDERATIONS

4.3.1 Cross-Section Geometry While I-shaped precast concrete girders are a mainstay for straight bridges, the development of precast concrete girders with tub-shaped cross sections, typically called U-girders and box girder sections, has enabled precast manufacturers to fabricate the full range of straight to curved precast concrete girder members. Precast concrete box girders can be fabricated without top flanges (open sections) or with top flanges (open or closed sections), as shown in Figure 4.3.1-1.

Out-of-plane and radial forces as well as torsion must be considered in the design and construction of curved bridges. The precast concrete girder shapes shown in Figure 4.2-2 have section properties that provide a stable girder when cast in a curve. Girders cast with open U sections have typically been able to sustain erection loadings prior to being closed during construction, which enhances their torsional strength and rigidity. As a rule, precast sections should be closed prior to applying any significant loadings during construction to prevent torsional cracking and unacceptable distortion.

Figure 4.3.1-1

Typical Cross Sections Suitable for Curved Girder Construction (Drawing: BergerABAM)

Webs of a box shape can be vertical (rectangular section) or sloped (trapezoidal or “tub” section). Sloped webs in precast concrete U-girders typically have a web taper of 4 to 1 that is consistent with standard practice in cast-in- place construction.

The depth of U-girder sections varies with the span length between piers. Curved precast concrete U-girder projects have generally employed constant-depth girders with depths between 48 and 84 in. for span lengths varying from 150 to 240 ft. Variable-depth girders have been used on bridge projects with span lengths in excess of 250 ft.

The primary longitudinal post-tensioning is placed in the precast girder webs. Web thicknesses must be proportioned to accommodate post-tensioning ducts. The AASHTO LRFD Bridge Design Specifications

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recommends that post-tensioning ducts occupy at most 40% of the web thickness. Using this criterion, web thicknesses that vary from 7.5 to 10 in. have been used to accommodate 3- and 4-in.-diameter ducts. The choice of web thickness must also consider the required shear, torsion, and principal tensile stresses.

Bottom slab width and thickness have been proportioned to accommodate the post-tensioning ducts and to supply adequate compression in negative moment regions. Top flanges of the U-girder section can be optimized to:

 Increase capacity for non-composite loading

 Enhance girder stability during erection

 Facilitate the placement of deck forms or precast deck panels

 Accommodate the placement of post-tensioning in negative moment regions

4.3.2 Span Length and Girder Segment Length Precast girder size is usually restricted by physical and legal limits on weight and length during handling and transportation. These limitations affect span lengths only when the girders span from pier to pier. Splicing enables this technology to be used for longer spans. The major determining factor affecting the feasibility of using spliced precast girders is the ability to support each girder segment during construction until it is self supporting. Increasing span lengths also requires deeper and heavier sections which may require shorter precast girder components and more splice locations in a span. Splicing curved girders requires temporary shoring to support girder segments and bracing to control out-of-plane forces during construction due to horizontal curvature.

Curved precast girders have typically been cast to lengths of about 120 ft with weights of approximately 260 kips. Shorter girders have been field-spliced and erected in lengths up to 150 ft and maximum weights of 350 kips. Girders have been fabricated with horizontal radii of curvature as low as 750 ft but can be designed to shorter radii if necessary. The radius of curvature can also be an important factor in determining individual girder lengths to enhance the global stability of the segments during construction.

Strength, serviceability, stability, and safety must be considered during all phases of the work, from taking the curved girder out of the casting form, to setting it in place at the site, and integrating the girder segment into the horizontally curved bridge. Currently the longest known span in the United States using curved precast concrete girders is approximately 260 ft, but analysis has shown that longer spans are achievable.

4.3.3 Lateral Bracing While strength considerations are well documented, there is currently no specific guidance in the LRFD Specifications that addresses design and serviceability requirements for bracing a curved concrete girder to resist torsional forces. This is particularly significant during construction where torsional forces are low and the impact of providing permanent bracing may be impractical. All LRFD Specifications requirements for internal bracing relate to steel curved girders and are not appropriate for precast concrete curved girders. Proper provisions are left to the design engineer’s discretion. Section 5.1 lists this and other issues that should be addressed by the appropriate AASHTO subcommittee.

Lateral bracing using steel sections has been designed to provide top flange bracing that does not significantly increase the weight of the precast concrete U-girder during construction. Temporary steel bracing is shown in Figure 4.3.3-1. The cost of welding or bolting connections to steel lateral bracing and the time required to accomplish this, have made the solution generally undesirable. An alternative to steel bracing that has been successful is a “lid slab” that is constructed to span across the top flanges of the precast U-girder between the webs. The lid slab closes the cross section, which greatly increases the torsional stiffness and strength of the girder. Lid slabs have been designed using thin cast-in-place concrete slabs or partial-depth precast panels that are grouted to reinforcement protruding from the tops of open girders, which become part of the composite concrete bridge deck. Similar technology is often used with conventional I-girder bridges as described in PCI 1988. Cast-in-place and precast concrete lid slabs are shown in Figures 4.3.3-1 and 4.4-3, respectively.

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Figure 4.3.3-1

Temporary Lateral Steel Bracing Installed in the Fabrication Plant (Photo: Precast/Prestressed Concrete Institute)

Figure 4.3.3-2

Curved U-Girders Shown Laterally Braced by Cast-in-Place Concrete Lid Slabs

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4.3.4 Post-tensioning Longitudinal post-tensioning has been used in curved precast girder bridges, in lieu of plant-installed pretensioning, to provide the design prestress force. The use of pretensioned strands has not been economically feasible to date due to the horizontal curvature, but could be effectively used with further development of the methodology. The size and location of the post-tensioning tendons is determined by the thicknesses of elements in the girder cross section.

The design of the post-tensioning in curved precast concrete girder bridges is very similar to conventional cast-in- place concrete box girder construction. Continuous tendons, typically placed in the webs in parabolic profiles, provide the primary load-resisting reinforcement. Placement of the tendons within the precast girder cross section determines the available eccentricity and effectiveness of the post-tensioning force. The location of ducts at the top of the webs in negative moment regions limits the available eccentricity of the post-tensioning force in the composite cross section. This typically controls the design. Supplemental tendons in negative moment regions can be accommodated in thicker top flanges increasing the section efficiency and extending span lengths.

The bottom flange of the U-girder cross section typically has ample room for post tensioning tendons to accommodate positive moments. Temporary and/or permanent tendons are used to resist construction loadings during handling and erection. These tendons are placed within each girder, typically in the bottom flange, and are stressed in the manufacturing plant prior to being shipped to the erection site. These tendons are also used, whenever possible, as part of the final design prestress force in positive moment regions. To avoid excessive friction losses, longer longitudinal tendons are typically stressed from both ends. In one project with particularly long continuous units, intermediate anchors were used to reduce the overall length of each of the web tendons. Figures 4.3.4-1 and 4.3.4-2 show layout and details, respectively, of the various types of tendons that have been used in spliced, curved U-girder bridge construction.

Figure 4.3.4-1

Example Girder Segment Arrangement and Post-Tensioning Layout (Drawing: PCI Zone 6 (SE Region) U Girder

Standards)

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Figure 4.3.4-2

Longitudinal Post-Tensioning Details at the Ends of Various Precast Girder Segments

4.3.5 Temporary Supports Spliced girder construction requires the use of temporary shoring until the precast girders are spliced and become self supporting following post-tensioning. Vertical shoring towers are typically used to support girder segments at each splice. Strongbacks or other special erection assemblies have also been used to support the ends of precast girders where support from the ground is not practical. A significant advantage of this type of construction is that it virtually eliminates the need for horizontal elements in the shoring as the girders are self- supporting between the vertical supports as shown in Figure 4.3.5-1a and 1b. This greatly simplifies design and construction of temporary structures. It also provides for traffic openings and a more cost-effective construction system. Combinations of vertical shoring and strongbacks have been used to provide openings for existing traffic up to 256 ft with little or no disruption to the site.

Figure 4.3.5-1

Erected Precast U-Girder Segments

a) Girder Segments Supported on

Piers and Temporary Shoring

Towers

b) Haunched Girder Segments Supported on Piers and Temporary Structures

Constructed with Simple Cast-In-Place Concrete Shoring Columns (Photo:

Precast/Prestressed Concrete Institute)

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Temporary supports and other special erection assemblies must be engineered to resist gravity, wind, and construction loads as well as provide a means to stabilize curved girders against rolling due to their curvature as shown in Figure 4.3.5-2. Bracing for out-of-plane forces, including torsion, is necessary to maintain the girder geometry during construction and casting of the deck slab. The design of temporary supports to stabilize the girders during construction is one of the more important considerations for this type of construction.

Figure 4.3.5-2

Example Erection Bracing Details

4.3.5.1 Requirement for Licensed Construction Engineer

The specifications for curved precast concrete girder projects using spliced girder construction should require full participation by a licensed engineer familiar with the design of temporary structures, heavy load erection, and use of post-tensioning to integrate curved girders into horizontally curved bridges during construction.

4.4 DETAILS

Many of the details associated with curved precast concrete girder bridges are taken from conventional post- tensioned, cast-in-place concrete box girder and precast girder construction. The condition of the final structure very closely emulates a cast-in-place concrete box girder bridge. Design details must address constructability issues at all stages from fabricating the girders to placing the concrete deck slab.

Each stage of construction involves a different set of specialists who are responsible for the unique issues that arise as the bridge is constructed. A successful project incorporates each specialist’s input as the bridge construction progresses. Issues that require detailed designs unique to this type of construction involve:

 Maintaining stability during all stages of construction

 Lifting and handling large precast pieces during shipping and erection

 Temporary support during construction

 Aligning the precast girders to achieve the correct geometry

 Installation, stressing, and grouting of post-tensioning tendons

 Resisting out-of-plane and torsional forces by closing the cross section

 Insuring predictable structural performance by limiting cracking during construction

 Providing for installation of bearings, expansion devices, and other necessary details that will be part of the permanent structure

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Many of these issues have been discussed in previous sections and others will be discussed in more detail in Section 4.5.

Fabrication of the precast girders requires that the precast manufacturer have a comprehensive understanding of the design issues that relate to the erection and post-tensioning of the structure. All embedded items must be properly placed and aligned to facilitate successful placement of the girders and the installation of the post- tensioning tendons and grout.

The curved girder is at its most unstable condition during precasting, handling, and erection. Once the girders are erected on temporary shoring, external bracing may be necessary to prevent rolling and to maintain the desired geometry until the girders are spliced. Issues relating to erection are described in greater detail in Section 4.5.2. Steel cross frames and thin concrete diaphragms have been designed at the ends of the precast girders to strengthen areas where temporary bearings and temporary erection bracing may be installed; see Fig. 4.4-1. Intermediate diaphragms are not usually necessary due to thicker webs that accommodate longitudinal post- tensioning.

Figure 4.4-1

End Diaphragms and Splice Details in Precast Girders

The following are extremely important issues to accomplish during construction:

 Properly align the girders on temporary shoring and brace them to achieve the proper geometry and avoid undesirable lateral loadings from alignment deviations in the post-tensioning

 Design for adequate confinement of the radial force from post-tensioning tendons in the webs and at girder splices to prevent blowouts or spalling due to radial forces

 Seal the ducts inside the girder splices properly to avoid leakage or cross-over grouting

 Properly detail the post-tensioning ducts to ensure they project from the ends of the precast girders to allow field personnel to adequately align and seal them prior to installing tendons and grout

 Ducts must have high point vents and low point drains to allow for removal of water prior to installing tendons and to properly vent air and grout

When the girders are erected they are generally supported on temporary shoring and on the permanent substructure. Curved girders are cast along the horizontal alignment but are typically cast flat and are not cambered to account for vertical curvature and deflections of the structure during construction and service conditions. The elevations of the temporary supports as well as the piers and abutments must consider the desired cambered elevation of the girders following construction.

To accommodate transitions in cross slope when girders are not cast in a warped or twisted configuration, the girders on either side of the splice are set to an average cross slope fall and the rotational angle as the transition is tapered through the splice. Severe cross slope transitions have been handled in this manner with little noticeable

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warping of the splice. This splice is generally 2 ft long and could be lengthened to hide the taper or allow the placement of more reinforcement to restrain post-tensioning lateral forces if a slight kink is induced in one or both alignments (horizontal and vertical). Closure placements have also been thickened to the interior of the U- girder to contain additional lateral reinforcement ties to resist bursting. Lateral deviations at these splices have been routinely accommodated to 5 degrees from the tangent. It is recommended that the center of rotation, as shown in Fig. 4.4-2, be one-half the height of the girder to minimize the misalignment of the webs and embedded post-tensioning.

Figure 4.4-2

U-Girder Center of Rotation

Once the girders are erected on temporary supports where they are spliced, diaphragms at the piers and abutments are cast. During this stage, the cross section, if it is an open, curved U-girder, will be closed to strengthen the cross section against torsion. The U-girder section is closed by casting a lid slab between the webs, as shown in Figure 4.3.5-1, or by installing precast concrete deck panels and casting a closure strip, or by filling pockets, to connect the panels to the top flanges of the precast girder. Figure 4.4-3 shows three panels that in addition to closing the tops of the girders, also spans the space between girders. The panels in Figure 4.4-4 cantilever beyond the girder flange to form the deck overhang. A steel form to manufacture and prestress the panels is shown in Figure 4.4-5a and panels in storage are shown in Figure 4.4-5b. Sample precast panel details are shown in Figure 4.4-6. Reinforcement must be detailed to provide an adequate structural connection between the lid slab and girder as well as provide adequate horizontal shear transfer between the girders and the composite cast-in-place concrete deck slab.

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Figure 4.4-3

Precast Concrete Panels are used to close the Tops of the Girders and Span between Girders (Photo:

Precast/Prestressed Concrete Institute)

Figure 4.4-4

Precast Concrete Panels Cantilever to Form the Deck Overhang (Photo: Precast/Prestressed Concrete Institute)

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Figure 4.4-5

Partial-Depth Precast Concrete Deck Panels (Photos: Precast/Prestressed Concrete Institute)

a) A Long-Line Steel Form Used to Cast and Prestress

Deck Panels

b) Deck Panels in Storage in a Manufacturing Plant

Figure 4.4-6

U-Girder Closure Details Using Precast Concrete, Partial-Depth Deck Panels

At every stage of construction following erection of the girders, the structure becomes stronger and more stable. By the time the deck slab is cast, the structure is a continuous, torsionally rigid structure that cambers significantly less than other types of construction. This makes predictions of elevations for deck casting more dependable.

4.5 FABRICATION, TRANSPORTATION, AND ERECTION

4.5.1 Fabrication

4.5.1.1 Forms

Forms for curved precast concrete girders must have enough adjustability to accommodate a number of varying geometric considerations in complex curved bridges. Curvatures will vary depending on the alignment of each bridge, and depths may vary depending on span lengths and vertical clearances. Forms may also need to accommodate girders with variable depths, and variable web and bottom flange thicknesses. In addition, formwork should be designed to accommodate special features such as integral diaphragms, and appendages for post-tensioning anchorages.

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Curved U-girders are fabricated using an exterior form that conforms to the horizontal alignment. The outer form can consist of a series of short straight chords or be a continuous curved shape as shown in Figure 4.5.1.1-1. Both methods have produced good results. Typically, the interior core forms consist of a number of short straight sections as shown in Fig. 4.5.1.1-2, chorded along the curve. The chorded core forms must maintain the design thickness of the web and flanges along the curve but are typically not curved themselves for simplicity.

Figure 4.5.1.1-1

Exterior Form Used to Cast Curved Girders (Photo:

EnCon Colorado LLC)

Figure 4.5.1.1-2

Chorded Interior Core Form for Casting Curved

Girders (Photo: EnCon Colorado LLC)

Forming for closed sections is similar to open U-girder casting but requires a secondary cast of a top flange or lid slab between the webs. The open U-girder is cast using a removable core form and a sacrificial form is later installed for the bottom of the top flange. The addition of a lid slab produces a much stronger section that is more stable, but the additional weight can be undesirable.

The cost of custom forms will increase costs for a single project. By designing curved bridges with standard sections that can be used on multiple projects, the cost effectiveness of this type of construction can be greatly enhanced. Many departments of transportation (DOTs) have developed their own standard sections. Cities and counties usually adopt the DOT standards in order to maintain consistency and to reduce the cost of fabrication.

4.5.1.2 Precasting

Straight girders are typically fabricated in conventional pretensioned beds, whereas curved girders require special formwork that can be adjusted for variations in curvature and are usually cast in separate beds. Fabrication issues such as concrete placement and typical reinforcement details are not significantly different for straight girders of similar shape. Currently, there are no PCI fabrication tolerances that specifically address curved precast concrete girder sections. Past projects have conformed to the owner’s specifications and current PCI fabrication tolerances for similar precast girder sections with acceptable results (PCI, 1999, and PCI, 2000).

As noted previously, due to horizontal curvature, precast concrete girders that require prestressing have all been post-tensioned. Post-tensioning that is anchored within each girder is stressed and grouted in the fabrication yard prior to shipping to the erection site. Figure 4.5.1.2-1 shows typical cross sections and reinforcement including post-tensioning ducts that installed in the fabrication plant. Currently there are no known commercial facilities that have casting beds capable of pretensioning curved girders.

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Figure 4.5.1.2-1

Girder Cross Sections and Typical Reinforcement Details

Curved girders require special design consideration for loadings during lifting, handling, and erection. Girder flexural and torsional stresses, crack control, and stability during plant storage, transport, and construction must all be considered. Lifting and temporary support locations should be specified to control rolling of the girders during handling, storage, and erection and to control handling stresses. Handling and construction stresses must be limited to control cracking during construction to avoid damaging the girders prior to incorporating them into the final structure. Conventional reinforcement as well as temporary and permanent post-tensioning have all been used successfully to control handling stresses before the girders are spliced and permanent post-tensioning is applied. Camber and creep deflections of girders during storage should also be considered.

In general, curved precast concrete girder reinforcement does not vary significantly from straight precast girders except that supplemental reinforcement is necessary around post-tensioning ducts to resist radial bursting forces. This supplementary reinforcement is particularly important at the ends of girders where kinks may form at splice locations. Anchorage areas to accommodate post-tensioning that is used in lieu of pretensioning, have been designed and detailed for various projects. While this introduces another variable, these same details occur in straight girder designs as well and are not specific to curved girder construction.

4.5.2 Transportation and Erection Open precast concrete U-girders are more easily fabricated in a single casting operation while closed box shapes are generally made with two casting operations. Open U-girders may provide economy in handling and erection due to their lighter weight. While the following discussion is focused on open U-girders, it is not intended to exclude other shapes that may be found to be more cost effective for specific projects.

At some point during construction, the open girders will require bracing and/or intermediate concrete diaphragms to protect the top flanges from buckling before the cast-in-place concrete bridge deck gains the required strength to act compositely with the girders. This may be accomplished during fabrication or on the jobsite.

The size and weight limitations of horizontally curved precast concrete segments often occur during handling and shipping. These limitations on transporting girders are important issues that designers need to investigate during preliminary design. Variables that influence the size and weight of girders include:

 Lifting capacity of cranes at fabrication yards

 Capability of trucks and trailers

 Experience of trucking companies

 Lane width restrictions during transport

 Limitations of overload haul permits by various agencies

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Special hauling rigs are commonly used to transport heavy permit loads in excess of 200,000 pounds in most states as shown in Figure 4.5.2-1. Curved precast girders have been manufactured and shipped with weights in excess of 200,000 pounds on some projects. Girders have been spliced and erected on site with lift weights in excess of 350,000 pounds. Erection is shown in Figure 4.5.2-2.

Figure 4.5.2-1

Curved Girders Ready for Transport (Photo: EnCon Colorado LLC)

Figure 4.5.2-2

Erection of Curved Girder Segments

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4.5.2.1 Girder Stability

The curvature of a girder results in a center of gravity that is offset from the straight line, or chord connecting the centers of the lifting points, or the shipping support points. The offset results in torsional moments along the length of the segment being handled or shipped. The torsional moments cause the girder to have a tendency to roll about the chord just defined. Methods to assure the stability of the girders must be implemented at all stages of handling, shipping, erection, and construction until the deck slab has gained adequate strength. The locations of support points during handling and on the haul truck must be established to address this issue.

Figure 4.5.2.1-1 illustrates the offset of the center of gravity of a curved girder from the chord. The offset is given for various precast girder lengths and degrees of curvature, assuming the chord is centered symmetrically within the arc of the girder. The offset times the total weight of the girder supported from its ends is the maximum total moment that would need to be resisted to prevent the girder from rolling. Examples of project data from two bridges built in Colorado are indicated as well. Ramp Y with a radius of 765 ft was transported in 118-ft-long segment lengths and an offset of 1.52 ft. Ramp K had a radius of 800 ft and was transported in 105-ft-long lengths resulting in an offset of 1.15 ft.

Stability must be assured during delivery. The preferred solution has been to locate supports so the center of gravity of the piece falls near the chord defined above. Usually, the leading end of the girder is cantilevered less than the trailing end due to space constraints from the tractor. The Colorado projects described in the preceding paragraph were safely hauled with supports that were a reasonable distance inboard as shown in Figure 4.5.2-1 without the need for any specialized bracing. The precast girders may also be braced on the transporting rig to provide additional support to resist rolling. Special rigs with a greater width between wheel lines would be necessary. Shorter girder segments could also be used in cases of very sharp curvature but this has not been necessary to date. Temporary stresses during transportation should be checked against allowable limits, similar to stress checks during storage or erection. In general, handling and hauling curved girders is not significantly different than straight girders. Specialized heavy haul trailers have become more commonly available in the industry. They are used to successfully transport large, curved precast girder segments and allay concerns about heavier hauling weights.

In areas where haul weight limitations are more restrictive, the engineer may specify or the precast manufacturer may request shorter girder segments that would allow the use of more conventional equipment. These segments could then be spliced and post-tensioned on the ground at the project site prior to erection. Alternatively, they could be set on temporary towers, spliced, and post-tensioned in their final positions. Very heavy, short segments have sometimes presented issues because their length has not allowed space for enough axles. When transporting very long girders, the haul route, super elevation, and intersections will need to be carefully evaluated.

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Figure 4.5.2.1-1

The Offset from a Straight Line to the Face of a Curved Girder Segment at its Midpoint due to Curvature

During handling in the plant of a PCI-certified producer and at the construction site, curved girders are prevented from rolling by locating lift locations inboard from the ends or with specialty rigging shown in Figures 4.5.2-2 and 4.5.2.1-2. When the girders are erected on falsework or on the permanent foundations, they must also be braced to prevent rolling as previously discussed in Section 4.3.5.

Figure 4.5.2.1-2

Lifting Details Showing a Typical Biased Spreader Bar (Drawing: PCI Zone 6 (SE Region) U Girder Standards)

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4.6 COST CONSIDERATIONS

Factors that affect the cost of curved precast concrete girder bridge construction include:

 Precast girder costs

 Special equipment and bracing for stability during construction

 Shipping and handling costs for hauling heavy sections

 Temporary shoring during construction

 Design features and additional reinforcement to resist radial forces

 Post-tensioning and grouting operations

The majority of these factors are not unique to curved precast concrete construction and are applicable to other types of bridge construction. Each type of curved bridge construction has unique cost implications that industry must evaluate for cost effectiveness.

The most significant factor affecting the economy of curved precast bridge construction is the precast girder cost. Many of the other factors that affect the cost of this type of construction relate to splicing the girders to accommodate longer spans and hauling heavier sections, which are not peculiar to curved girder construction. Precast girders cast on a curve are more expensive to design and construct than straight bridges. Precast girder costs on initial projects were 50% to 75% greater than a comparable straight section. As more curved precast girder bridges have been built and formwork and startup costs have been amortized, the premium for curved precast girders has been greatly reduced, in some cases to approximately 10 to 25% of typical straight girder costs.

As contractors gain more familiarity with curved precast girder bridge construction and develop means and methods to deal with issues of handling, erection, and temporary support, the cost of this type of construction will become increasingly more cost effective.

4.7 PROJECT STUDIES

Several curved precast concrete girder projects are described in this section. Six of those case studies are transit systems, two are highway bridges, and there is a summary overview of several projects in Colorado. The projects are presented in chronological order of their construction beginning with the early monorail bridges, followed by the Philadelphia Airport and Arbor Road bridges, and then the Colorado U-girder bridges.

Some the earliest applications of curved precast concrete girders were on several elevated transit or people- mover projects. These monorail projects all used a similar adjustable forming system to fabricate the guideway girders. Girders were fabricated to the true horizontal curvature, vertical curvature, and superelevation.

4.7.1 Seattle Monorail

4.7.1.1 Project Information

Project Name—Seattle Monorail

Location—Seattle, Wash.

Owner—City of Seattle

Dates of Letting, Construction, and Completion—Most of the work was done in 1961 and the project opened in March 1962

4.7.1.2 Structural System

The 5,000-ft-long Seattle Monorail in Washington State, built in 1962, was constructed using simple-span curved precast concrete girders that span from column to column. It is shown in Figure 4.7.1.2-1. The top and side surfaces of these girders directly support the vehicle load and guide rubber tires. Torsional end moments are

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resisted by high-strength bolts (oriented in the direction of the center of radius) on the inside of the horizontal curves that secure the guideway girders to the supporting crossheads. The structure remains in use today. In June 2008, the Red Monorail Train reached its one millionth mile of service.

Figure 4.7.1.2-1

Monorail Transit System, Seattle, Wash. (Photo: BergerABAM)

4.7.1.3 Construction

The guideway was constructed using cast-on-site precast columns and crosshead units bolted to drilled shaft foundations. The girders were manufactured in Tacoma, Wash., (approximately 30 miles south of the site) and were bolted to pier crossheads. Curved girders were manufactured to 250-ft-long radii with span lengths up to 56 ft. Spiral transitions were used between curved and tangent sections of the alignment. The guideway incorporating 130 girders and 65 columns was constructed in 10 months.

4.7.1.4 Lessons Learned

The project proved that curved precast concrete girders could be fabricated to stringent tolerances using specially designed formwork and good geometry quality control practices (PCI, 1999).

4.7.2 Disney World Monorail

4.7.2.1 Project Information

Project Name—Disney World Monorail

Location—Orlando, Florida

Owner—Walt Disney World Corporation

Dates of Letting, Construction, and Completion—

Initial project—1969 to opening in October 1971

Extension opened October 1982

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4.7.2.2 Structural System

The construction of the landmark 7-mile-long monorail at Disney World in Florida (PCI Design Awards, 1972) also used curved precast concrete haunched box girders as shown in Figure 4.7.2.2-1. Like other monorail systems, the top and side surfaces of these girders directly support the vehicle load and guide rubber tires. The guideway is primarily composed of six-span continuous girder units, 580-ft-long with typical spans of 90, 100, 100, 100, 100, and 90 ft.

4.7.2.3 Construction

The guideway structure was constructed using straight and curved precast haunched beams supported on precast columns and, at certain locations, structural steel crossheads. Guideway beams span from column to column. Special steel beam hangers and bottom keeper assemblies were used to erect the curved beams and to resist torsional beam end moments during erection. Special formwork with computer generated geometric settings was used to manufacture precast concrete beams to the required tolerances. Computer settings were used to translate the three-dimensional beam in its final spatial alignment, profile, and superelevation to a best-fit position for casting the beams in the special adjustable forms. Beams were typically integrated into six-span continuous structures through the use of closure pours over columns and field post-tensioning.

Figure 4.7.2.2-1

Disney World Monorail Transit System in Florida (Photos: Previously published by the Precast/Prestressed Concrete

Institute)

a) Girders Supported on Columns b) Girders Supported on Steel Crossheads

4.7.2.4 Lessons Learned

Fabrication, bunking, transportation, and erection of these curved beams were carefully considered in the beam, precast column, and crosshead design. Providing a proposed method of field construction into the project documents translated into erection speed and cost savings to the project owner.

4.7.3 Las Vegas Monorail

4.7.3.1 Project Information

Project Name—Las Vegas Monorail

Location—Las Vegas, Nev.

Owner—Las Vegas Monorail Company, Las Vegas, Nev.

Dates of Letting, Construction, and Completion—2002 to 2004

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4.7.3.2 Structural System

The 3.9-mile-long Las Vegas Monorail in Nevada also used curved precast concrete haunched box girders for the guideway in 2003 and shown in Figure 4.7.3.2-1. The structural system was modeled after the Walt Disney World Monorail guideway. However, the Las Vegas Monorail guideway is composed of cast-in-place concrete columns and crossheads and typical four-span continuous units. As with other monorail systems, the top and side surfaces of these beams directly support the vehicle load and guide rubber tires.

4.7.3.3 Construction

Special assemblies were fabricated to lift and erect the curved guideway beams. This monorail guideway system was the first to use an emergency walkway for vehicle evacuation and for maintenance. Special forms, modeled after the forms used to fabricate the Walt Disney World Monorail beams, were used to fabricate the curved beams to stringent tolerances.

Figure 4.7.3.2-1

Monorail Transit System in Las Vegas, Nev. (Photos: BergerABAM)

4.7.3.4 Lessons Learned

Curved precast girders can be efficiently produced in special forms using a combination of manufacturing and construction technologies.

4.7.4 Expo 86 Vancouver SkyTrain

4.7.4.1 Project Information

Project Name—Expo 86 Vancouver SkyTrain

Location—Vancouver, British Columbia, Canada

Owner—Urban Transit Authority, Vancouver, British Columbia, Canada (operated by British Columbia Rapid Transit Company)

Dates of Letting, Construction and Completion—

Construction began March 1982

Limited opening December 1985

Full services January 1986

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4.7.4.2 Structural System

The 9-mile-long Expo 86 Vancouver SkyTrain in British Columbia, Canada, is a steel wheel and steel rail transit system that was constructed using straight and curved precast concrete box girders that typically span 92 to 108 ft between supporting columns. The project is described in detail in Vancouver Guideway, 1983 and Nettles and Lowe, 1988. The Skybridge crossing of the Fraser River was designated a 1989 PCI Design Award winner. Typical structures are dual lane, and typical guideway structural units are two-span continuous structures. Continuous units were constructed using cast-in-place concrete closure pours at the beam fixed ends with field post- tensioning. The length of continuous structure was limited by the need to control the structure and continuous welded rail interaction forces. Over one-half of the 1,100 girders on the project were horizontally curved as seen in Figure 4.7.4.2-1. The expansion ends of the continuous units were supported on a single bearing. Torsional load effects were transferred to the fixed crosshead and columns by the torsionally stiff box beams.

Figure 4.7.4.2-1

Expo 86 SkyTrain Transit System in Vancouver, British Columbia, Canada (Photos: BergerABAM)

4.7.4.3 Construction

Curved precast concrete girders were fabricated in “special forming machines,” a term used by the precast concrete manufacturer. Prototypes of these special forms were provided to the precast concrete manufacturer by the transit vehicle manufacturer. Data for setting these forms to translate the spatial three-dimensional geometry into local formwork coordinates were also provided to the beam manufacturer. Special 13-axle transport trailers were built to haul the guideway girders from the manufacturing plant to the project site. Six beams—a city block length—of guideway were erected each day. The guideway supports continuously welded, 135 lb/ft steel rails that were fixed to the deck of the guideway beams with direct fixation fasteners and inserts that were cast into the precast concrete beams.

4.7.4.4 Lessons Learned

Shared risk between the general contractor and the precast concrete manufacturer for controlling beam geometry and production worked well. No beams were rejected.

4.7.5 Detroit Central Area Transit System

4.7.5.1 Project Information

Project Name—Detroit Central Area Transit System

Location—Detroit, Mich.

Owner—City of Detroit, Detroit Transportation Corporation, Detroit, Mich. (formerly owned by Southeast Michigan Transportation Authority)

Dates of Letting, Construction and Completion—1984 to 1987

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4.7.5.2 Structural System

The 2.9-mile-long Detroit, Mich., Central Area Transit System (CATS) was constructed using horizontally curved precast concrete box girders shown in Figure 4.7.5.2-1. Horizontal radii of curvature were as short as 115 ft on this project. The curved girders were fabricated in special forms that were modeled after the forms that were used to construct the Expo 86 SkyTrain guideway in Vancouver, British Columbia.

Structures were single lane. The guideway supports a continuously welded, 135 lb/ft steel rail that was directly fixed to the deck of the guideway girders. Typical guideway units were two- to three-span continuous structures. Continuous units were constructed using cast-in-place concrete closure pours at the beam fixed ends and field post-tensioning. Some curved guideway structures traversed a 90-degree turn on a 115 ft radius. For these structures, midspan shoring was used to erect the beams to resist the beam torsional overturning effects. The shoring remained in place until the beam was fully integrated into a continuous three-dimensional beam-column frame unit. This construction system also reduced the torsional demands on the box girders.

4.7.5.3 Construction

Curved precast concrete girders were fabricated in special forms that were chorded in 5-ft lengths. As stated above, erection of the longer-span, tightly-curved precast girders was assisted by placing shoring at or near the beam midspan until the girders were fully integrated into the supporting columns and into continuous structural units. Data for setting these forms to translate the spatial three-dimensional geometry into local formwork coordinates were also provided to the precast manufacturer.

Figure 4.7.5.2-1

Central Area Transit System in Detroit, Mich. (Photo: BergerABAM)

4.7.5.4 Lessons Learned

Similar to the Vancouver Expo 86 SkyTrain guideway, there was a shared risk between the general contractor and the precast concrete manufacturer for controlling girder geometry and production, which worked well. No girders were rejected.

Concrete box girders can be used at radii as short as 115 ft. Midspan diaphragms were required to control distortion-induced moments inside the tightly curved box girder cross section. Care also needs to be exercised to properly secure the tightly curved tendons from bursting out of girder web walls.

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4.7.6 Getty Center Tram Guideway

4.7.6.1 Project Information

Project Name—Getty Center Tram Guideway

Location—Near Los Angeles, Calif.

Owner—J. Paul Getty Museum Trust, Santa Monica, Calif.

Dates of Letting, Construction and Completion—1992 to 1994

4.7.6.2 Structural System

The 2,625-ft-long Getty Center Tram Guideway is located near Los Angeles, Calif. (Josten et al., 1995) and is shown in Figures 4.7.6.2-1 and 2. It has a total length of tram guideway of 3,625 ft, which includes at-grade segments at each end. Precast concrete horizontally curved girder segments and an open-top U-girder section were used to construct an aesthetically pleasing curved guideway structure. The cross section of the guideway is shown in Figure 4.7.6.2-3. This guideway supports a cable-propelled, air-cushion-supported vehicle. The vehicle essentially flies on the guideway on a cushion of air. The guideway structure is a single-lane structure with a bypass section near the center of the system. Girders were made into four- to six-span continuous units. Earthquake forces were transferred from beams through solid steel lugs into precast concrete crossheads supported by columns and drilled shaft foundations. Torsional effects in this open U-section girder were resisted by web shear forces and deck bending at or near the supporting columns. Curved girder span lengths were 67.5 ft with a horizontal radius of 210 ft.

Figure 4.7.6.2-1

Aerial View of Getty Center Tram Guideway With the Access Road on the Right (Photo: A. T. Curd Constructors)

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Figure 4.7.6.2-2

A Portion of the Curved Getty Center Tram Guideway (Photo: A. T. Curd Constructors)

Figure 4.7.6.2-3

Cross Section of the Getty Center Tram Guideway (Drawing: A. T. Curd Constructors)

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4.7.6.3 Construction

Adjustable wood forms were used to fabricate these curved precast concrete girder segments. AutoCAD software was used to develop each precast element in its spatial geometry and then rotate the piece into its geometry in the forms. Precast web beam construction permitted casting over 10,000 inserts directly into the concrete to a tolerance of ⅛ in. Two precast curved-beam L-sections connected with a cast-in-place deck slab spanning from pier to pier were used to make up the U-section girder as shown in Figure 4.7.6.3-1. Precast stem beams spanned from column to column and were designed to support the deck slab during casting. Girders were made into continuous span units though beam closure pours and field post-tensioning. A steel-troweled flying surface was cast on top of the beam deck slab to interface with the vehicle air cushions. Precast concrete crossheads were designed at the request of the general contractor to facilitate guideway erection on the constricted site.

Figure 4.7.6.3-1

A Section of Guideway with Two Curved L-Beams is shown During a Mock-Up in the Precast Plant. Precast

Crossheads In the Foreground Have Troughs to Receive Precast Stem Beams. (Photo: A. T. Curd Constructors)

4.7.6.4 Lessons Learned

Close interaction between the precast manufacturer, general contractor, inspectors, and designers was a key to the successful completion of this structure. On January 10, 1994, the structure’s final punch list inspection was conducted. On January 17, 1994, the Northridge earthquake struck the area. The Getty Tram Guideway came through the earthquake with high marks. No damage from the reported 0.50-g ground accelerations at the site was observed (other than expansion joint seals coming undone).

4.7.7 I-95 Airport Ramp Bridge A five-span, curved, precast concrete girder bridge was designed and constructed in 1983 to provide a ramp from I-95 into the Philadelphia, Pa., airport (Barnoff et al., 1984) and is shown in Figure 4.7.7-1.

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Figure 4.7.7-1

Completed I-95 Philadelphia, Pa., Airport Ramp Bridge (Photo: Schuylkill Products, Inc.)

4.7.7.1 Project Information

Project Name—I-95 Ramp at the Philadelphia Airport

Location—Philadelphia International Airport, Philadelphia, Pa.

Owner—Pennsylvania Department of Transportation (contact information)

Dates of Letting, Construction and Completion—Project Completed in 1983

4.7.7.2 Structural System

The 40-ft-wide bridge consists of a cast-in-place concrete deck supported on five lines of curved precast, post- tensioned box girders that were made continuous over two and three spans. Approximate span lengths are 139 and 126 ft for the two-span units and 92, 135, and 92 ft for the three-span units. The radius of curvature is 478 ft for the two-span units and 326 ft for the three-span units. Curvature was achieved by casting girders in 20-ft-long chords along the horizontal alignment. The girders are shown during construction in Figure 4.7.7.2-1. The segments were assembled and post-tensioned into full girder lengths in the fabrication plant. An assembled girder is shown in Figure 4.7.7.2-2.

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Figure 4.7.7.2-1

Chorded Curved Girders in the I-95 Philadelphia, Pa., Airport Ramp Bridge (Photos: Schuylkill Products, Inc.)

a) Top View of Girders Shown During Construction b) View From Under Curved Girders Prior to

Casting Bridge Deck

Figure 4.7.7.2-2

Assembled and Post-tensioned Girder in the Precasting Plant (Photo: Schuylkill Products, Inc.)

The precast girders were a closed box section, 5 ft deep and 4.5 ft wide with 5-in.-thick webs. The girders were partially post-tensioned for hauling and erection loadings during fabrication. Girders were erected and field spliced at interior piers and stage post tensioned for continuity. All prestress consisted of external post- tensioning placed inside the box girders. The concrete deck slab was cast in place.

4.7.7.3 Construction

The project used a framing system of curved precast concrete box girders that were spliced over the interior piers and post-tensioned for continuity using external tendons. The curved girders were cast in short straight sections that were kinked along the girder length to create the curved girder from pier to pier. Girder lines were connected with transverse concrete diaphragms at the piers and abutments.

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4.7.7.4 Lessons Learned

The project was the first of its kind to demonstrate that curved precast girders can be used for urban bridges with tightly curved alignments. The project was successfully prefabricated and constructed and remains in service. The innovative methods that were developed for this project were not repeated for another 23 years, until the design and construction of the Arbor Road Bridge, which is described in the following section. This was due, in large part, to the small size of the project which resulted in significant start-up costs relative to the overall cost of construction and the lack of support for similar projects by local owner agencies.

4.7.8 Arbor Road Bridge

4.7.8.1 Project Information

Project Name—Arbor Road Bridge

Location—Lancaster County, Neb.

Owner—Nebraska Department of Transportation (contact information)

Dates of Letting, Construction and Completion—Completed in July 2006

4.7.8.2 Structural System

The Arbor Road Overpass Bridge that crosses I-80 in Lancaster County (Omaha), Neb., is a two-span, curved precast concrete girder bridge as reported in Sun et al., 2007. It is 277 ft long and 38 ft wide with 142- and 136-ft- long spans. The project, a value engineering alternate to a steel box girder bridge, was designed and constructed in 2004. The superstructure consists of four lines of continuous curved precast concrete girders supporting a full- depth precast deck and is shown under construction in Figure 4.7.8.2-1.

Figure 4.7.8.2-1

Curved Rectangular Girders During Construction in the Arbor Road Bridge, Lancaster County, Neb. (Photo:

Chuanbing Sun, e.construct.USA, LLC)

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The girders were precast from pier to pier along a 1,200-ft-radius horizontal curve in 40-ft-long chorded sections. The rectangular, U-shaped girders were approximately 46 in. tall and 48 in. wide with 8-in-thick webs and a 5-in.- thick bottom flange. Unbonded post-tensioning was stressed in the girders for transportation and erection loadings. Continuity post-tensioning consisted of four ducts each with fifteen 0.6-in.-diameter tendons. The post- tensioning was placed in parabolic profiles in the girder webs and spliced in the closure over the interior pier. Continuity post-tensioning was stressed in two stages during erection.

The girders were erected on temporary supports at each face of the interior pier. A closure was cast and the first stage of continuity post-tensioning was stressed. Full-width, full-depth, precast deck slabs were erected and grouted, a concrete overlay was placed, and the final stage of post-tensioning was stressed into the composite structure. Figure 4.7.8.1-2 is a view of the completed bridge.

Figure 4.7.8.2-2

Completed Arbor Road Bridge in Nebraska (Photo: Sun et al. 2007)

This project demonstrated that curved precast concrete girder highway bridges can be constructed, using established means and methods, at a significant cost savings to more established methods of construction.

4.7.8.3 Construction

The framing system comprises curved precast concrete U-girders that were spliced over the interior piers and post-tensioned for continuity using internal tendons in the girder webs. The project used a concept similar to the Philadelphia Airport Bridge. The curved girders were cast in short straight sections that were kinked along the girder length to create the curved girder from pier to pier. Girder lines were connected with steel diaphragms along the girder length and transverse concrete diaphragms at the piers and abutments. The deck consists of full- width, full-depth precast concrete deck panels with a concrete overlay. These panels are shown during installation in Figure 4.7.8.3-1.

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Figure 4.7.8.3-1

Full-Depth, Full-Width Precast, Prestressed Concrete Deck Panels on the Arbor Road Bridge (Photo: Maher K.

Tadros, e.construct.USA, LLC)

4.7.8.4 Lessons Learned

The project was designed and constructed as a value engineering alternate to a steel bridge and was constructed at a cost that was less than the budget for the original design. This was the first chorded, curved precast girder bridge constructed in the United States in 23 years and clearly demonstrated that curved precast girder construction represents a viable economical alternate to established methods of construction for curved bridges.

4.7.9 Curved Precast U-Girder Projects in Colorado Since 2005, curved precast concrete U-girders have been used on nine bridge projects in Colorado (Reese, 2008). The use of commercially produced curved precast concrete girders provides an economical and aesthetically appealing alternative to steel and cast-in-place concrete construction. The number of projects constructed in such a short period in one area has been extremely important in reducing bridge construction costs and advancing this technology. Colorado precast concrete plants have been progressive in partnering with the local engineering and construction community to develop this as an economical and sustainable technology. Currently there are more bridges of this type in service in Colorado than in all other states combined.

The majority of the Colorado bridges are flyover ramps that have been added to existing urban interchanges (Reese, 2010). An example is the I-25 project in Trinidad, Colo., which consists of an elevated viaduct for the Northbound and Southbound main line with entrance and exit ramps. Another example is the Austin Bluffs Bridge.

Maximum spans for the Colorado bridges ranged from 160 to 235 ft for constant depth cross sections and up to 256 ft for spans with haunched girders. Girder depths have varied from 72 to 86 in. for constant depth sections, up to a 114-in.-deep haunched section. Girder spacing up to 26 ft on center have been used to support a number of different deck configurations. Table 4.7.9-1 summarizes all the curved precast concrete U-girder projects in Colorado that have been designed and built since 2005. Table 4.7.9-2 adds information about the project location and owner. Photos of some of these bridges are shown in Figure 4.7.9-1a-h.

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Table 4.7.9-1 Summary of Curved Precast Concrete U-Girder Bridges in Colorado

Project Name Year Built

Type of Girder

Max. Span Length, ft

Horizontal Curvature, ft

I-25/SH 270 Flyover Ramp K 2005 CDOT U84 200 800

SH 270/I-76 Flyover Ramp Y 2006 CDOT U84 230 765

C-470/I-70 Flyover Ramp H 2006 CDOT U84 200 1,200

Austin Bluffs Parkway over Union Boulevard

2007 CDOT U84 210 800

NB & SB I-25 Viaduct, Ph I 2008 CDOT U78 Haunched

256 1,200

I-70/SH 58 Flyover Ramp A 2008 CDOT U84 girder

231 830

NB & SB I-25 Viaduct, Ph II 2010 CDOT U78 Haunched

256 1,200

C-470/Santa Fe Blvd Flyover Ramp

2011 CDOT U72 160 900

I-25/Santa Fe Blvd Ramp 1 2013 CDOT U72 200 1,100

Table 4.7.9-2 The Location and Owners of Curved Precast U-Girder Bridges in Colorado

Project Name Location Owner

Park Avenue Overpass Denver Colorado DOT

I-25/SH 270 Flyover Ramp K Denver Colorado DOT

SH 270/I-76 Flyover Ramp Y Denver Colorado DOT

C-470/I-70 Flyover Ramp H Aurora E-470 Toll Authority

Austin Bluffs over Union Blvd. Colorado Springs City of Colorado Springs

NB & SB I-25 Viaduct, Phase I Trinidad Colorado DOT

I-70/SH 58 Flyover Ramp A Denver Colorado DOT

NB & SB I-25 Viaduct, Phase II Trinidad Colorado DOT

C-470/Santa Fe Blvd Flyover Ramp Denver Douglas County

I-25/Santa Fe Blvd Ramp 1 Denver Colorado DOT

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Figure 4.7.9-1

Curved Concrete U-Girder Bridges in Colorado

a) Austin Bluffs Parkway over Union Boulevard,

Colorado Springs, Colo.

b) I-25/SH 270 Ramp K, Denver, Colo.

c) I-25 Viaduct, Trinidad, Colo. (Photo: Plum Creek

Structures) d) I-70/SH 58 Ramp A, Golden, Colo.

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e) I-25 Viaduct, Trinidad, Colo. (Photo:

Precast/Prestressed Concrete Institute) f) I-76/SH 270 Ramp Y, Denver, Colo.

g) C-470/I-70 Ramp H, Aurora, Colo. h) C-470/Santa Fe Boulevard, Denver, Colo.

The curved precast concrete bridges in Colorado have firmly established this concept as a viable option for long- span structures of all types of roadway geometry in the most challenging conditions. The Colorado experience has demonstrated that this technology is viable and has a strong future in bridge construction.

4.7.9.2 Construction

All of the Colorado projects use a framing system of curved precast concrete U-girders that were spliced within the spans and post-tensioned for continuity using internal tendons. The curved girders were cast in curved shapes that conform to the various horizontal alignments of each bridge. Decks are generally cast-in-place concrete slabs and occasionally full-width partial-depth precast panels with cast-in-place composite concrete topping.

4.7.9.3 Lessons Learned

The Colorado projects demonstrate that the concept of curved precast concrete construction, when supported by owner agencies, can result in an extremely cost-effective, aesthetically-pleasing solution. In less than a decade, it has become the most common solution in the state, in urban areas, for complex long-span bridge construction with curved alignments.

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5.0 NEEDED RESEARCH AND CONCLUSION

5.1 FUTURE RESEARCH

A number of areas needing future research are suggested to advance and accelerate the use of horizontally curved precast concrete bridge girders:

Consistent design requirements—Consideration of issues related to design requirements such as future post- tensioning, structural redundancy, and access for safety inspection and maintenance that are consistent with other methods of construction should be identified and established within the AASHTO specification provisions for this type of construction. These issues need to be addressed in both the design and construction specifications.

Design guidance on concrete torsion—Design guidance is needed on acceptable levels of concrete torsion for girders in the noncomposite condition during handling and erection. Current LRFD Specifications do not provide guidance on bracing design of open concrete sections or acceptable torsional stresses without the lid slab. In the examples described in Section 4, the designer chose a service limitation of one-half the cracking torque.

Lightweight concrete—Similar to considerations for straight girders, the use of lightweight or semi-lightweight (controlled density) concrete for curved girders would be very beneficial. It has the potential to greatly enhance the performance and economy of precast girder construction by increasing span lengths, girder spacing, and reducing transportation and erection costs.

High performance materials—The use of high performance materials such as high compressive strength concrete can significantly reduce the amount of internal reinforcement needed to meet design requirements. This would reduce complexity and labor costs involved in production. Another example of high performance materials that can enhance the fabrication of precast concrete girders is self-consolidating concrete (SCC). SCC provides quality concrete in thin plate elements. Also, carbon-fiber or glass-fiber materials for post-tensioning tendons could enhance the corrosion resistance to extend the useful life of concrete girders.

Efficient cross sections and longer spans—Use of typical precast concrete bulb-tee girders in horizontally curved applications can increase the use of precast concrete in bridges. Precast girder bridges can be economically designed for long-span applications using extradosed1 and cable-stayed construction in situations that allow temporary shoring during construction. Longer-span bridges can eliminate piers for economy and reduce environmental impacts. Use of sections that employ thin plate elements in conjunction with other possible industry advances can increase span lengths and reduce the material costs of curved precast concrete girders.

External tendons—External post-tensioning can be used in precast girder construction with U-girder and box girder sections to allow for thinner sections, address challenges of limited spacing for post-tensioning in negative moment regions, and increase girder capacity. External tendons can also be designed to be inspected and to be replaced or increased in the future if required. External post-tensioning inside the concrete box is a mature technology widely used in segmental box girder construction and can easily be incorporated into precast girder construction to enhance the variety of design options available to structural designers. Existing details and construction procedures and specifications for segmental bridges can be easily applied to precast girders as well.

1 Note: An extradosed bridge is defined as a hybrid of cable-stayed and girder type (segmental, CIP, or other type) bridge technologies. It can also be classified as a transition between a conventional prestressed concrete bridge and a cable-stayed bridge. It behaves much like a prestressed concrete girder bridge with external prestressing. In an extradosed bridge the vertical shear is carried by both the cables and the supported superstructure. In general, if a vertical load is placed at midspan on a girder bridge the entire vertical load is carried back to the tower in girder shear and then to ground. If a vertical load is placed midspan on a cable-stayed bridge the entire vertical load is carried up through the stays to the tower and down to ground, i.e. none is carried in shear. In an extradosed bridge the vertical load is carried partly in shear and partly in the cables.

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5.2 CONCLUSION

Commercially produced precast concrete girders provide an economical and aesthetically appealing alternative to steel and cast-in-place concrete construction for horizontally curved bridges. Straight girders of various shapes can be chorded from pier to pier for a simple and cost-effective solution.

If aesthetics become undesirable due to the contrast of the straight outside girder relative to the curved edge of the deck, the straight precast concrete girders may be field spliced at one or two locations within the span. Spliced girder construction has great potential to expand the use of precast concrete in the construction of urban interchanges, overpasses, and viaduct bridges with complex roadway geometry that requires longer spans and sharper horizontal curvatures. The number and location of splices within each span can be designed to enhance the structural efficiency, constructability, and aesthetic appeal of a structure by more closely simulating the appearance of a curved girder bridge while using straight sections, which are typically more economical. The longer spans that are normally associated with spliced girder construction also reduce the visual impact of the offset of the straight girders which further enhances the overall appearance of the bridge.

Alternatively, the girders may be continuously curved to conform to the curved alignment. Continuously curved precast concrete girder highway bridges have used post-tensioned U-girders, box girders, segmental, and decked box girders. Precast concrete U-girders provide a robust cross section that is internally stable when cast on a curve and prestressed. The design community and construction industry have developed a number of methods using curved precast concrete U-girders to address the complexity of constructing bridges with different curvatures and severe geometric design conditions.

Curved precast concrete girder bridges have been shown to be a viable option for long-span bridges of all types of roadway geometry in the most challenging conditions. The solutions described in this report have used existing means and methods in local environments with nominal startup costs. Segment weights and the resulting transportation and erection issues can be significant, but certainly not insurmountable. The use of horizontally curved precast, prestressed concrete girder bridges is restrained by the lack of ingenuity on the part of fabricators and bridge engineers, and the availability of information about what has already been accomplished and the technology involved.

Many successful projects have been described in this report. These bridges, beginning with the early monorail guideways to the more recent highway bridge in Nebraska and the numerous highway bridges in Colorado, have demonstrated that curved, or chorded-segment precast concrete construction, represent viable curved bridge options to owners when constructing capacity improvement projects in urban environments requiring longer spans and complex geometry.

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CITED REFERENCES

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