Ethics Essay

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NTSB’s FIU Bridge Collapse Investigation Finds Many Problems The agency published 30 �ndings as part of its presentation on the bridge collapse’s probable cause

The National Transportation Safety Board included numerous technical reports on the FIU bridge collapse, along

with a video summarizing the events leading up to the March 15, 2018, tragedy. (Image courtesy NTSB)

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October 23, 2019

Scott Judy and Tom

Ichniowski

During its three-hour-plus-long presentation on the cause of the Florida

International University pedestrian bridge collapse, of�cials with the National

Transportation Safety Board referred to its roughly 18-month-long

investigation as one of its most complex.

NTSB Chairman Robert Sumwalt noted that he’s been on the safety board for 13 years and deliberated over

nearly 200 accidents. He said, “I don’t think I’ve ever seen one where there’s more �nger-pointing between

the parties. And you know, the �nger-pointing is actually correct. Everybody’s pointing at everyone else.

 In fact, that is correct—because everyone shares a piece of this accident. There were errors up and down

the line.”.

As part of its Oct. 22 presentation into the bridge collapse’s probable cause, the NTSB listed 30 �ndings

from its investigation. The �ndings are included as part of the NTSB’s abstract report, the full version of

which readers can �nd here.

As the agency notes in its abstract, “The �nal report and pertinent safety recommendation letters will be

distributed to recommendation recipients as soon as possible. The attached information is subject to

further review and editing to re�ect changes adopted during the Board meeting.”

Due to the list of �ndings' length, for our readers’ convenience—and to invite possible reader comment

and discussion—ENR is publishing all of these �ndings here, in their entirety, without editing.

Findings

1. The emergency response by local �re departments and law enforcement personnel was timely and

adequate.

2. The concrete and steel materials used during construction of the pedestrian bridge were not a factor in

its collapse.

3. The hydraulic jack used to post-tension the steel rods in member 11 was operating as expected at the

time of the bridge collapse.

4. (1) The FIGG Bridge Engineers (FIGG) bridge design was nonredundant because it provided only a

singular load path, (2) FIGG used poor judgment when it determined the bridge was a redundant structure,

and then, (3) FIGG erroneously used a redundancy factor of 1.0, which is commonly used for structures

with redundant load paths.

5. Even if the cold joint surface of nodal region 11/12 had been roughened to a 0.25-inch amplitude, node

11/12 would not have had suf�cient capacity to counteract the demand load for interface shear—and the

bridge would still have been under-designed and could have failed.

6. The FIGG Bridge Engineers construction plans inconsistently identi�ed when intentionally roughened

surfaces were needed to ful�ll the assumptions of the bridge design.

7. Because FIGG Bridge Engineers (1) did not use the lower bound load factor for determining the

governing net compression, Pc, in the interface shear; and (2) incorrectly increased and ampli�ed the

effects of the clamping force across the interface shear surface, its bridge design calculations resulted in a

signi�cant overestimation of capacity.

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8. FIGG Bridge Engineers (1) made signi�cant design errors in the determination of loads, leading to a

severe underestimation of the demands placed on critical portions of the pedestrian bridge; and (2)

signi�cantly overestimated the capacity of the member 1/2 and 11/12 nodal regions.

9. Based on analytical modeling results, FIGG Bridge Engineers should have considered the loadings from

all critical construction stages when designing the pedestrian bridge and determining the governing

interface shear demands.

10. In several instances throughout the bridge design process, the FIGG Bridge Engineers models produced

reasonable estimations for interface shear demand, but these values were not always used in the design of

truss members to resist force demands.

11. FIGG Bridge Engineers’ analytical modeling for the bridge design resulted in a signi�cant

underestimation of demand at critical and highly loaded nodal regions.

12. The concrete distress initially observed in nodal region 11/12 is consistent with the underestimation of

interface shear demand and the overestimation of identi�ed capacity in the bridge design.

13. The FIGG Bridge Engineers design of the rebar placement in node 11/12 resulted in less reinforcing

steel being available and diminished resistance to the critical interface shear demand, which contributed

to the collapse of the bridge.

14. The member 11/12 nodal region contained nonstructural voids (four hollow vertical pipe sleeves and

the horizontal drain pipe) within the concrete that made it less able to resist applied loads, which

contributed to the destabilization of this node through overstress and the subsequent collapse of the main

span.

15. Although it may be generally accepted that concrete itself is susceptible to cracking, the rate of

premature concrete distress was clear evidence that the structure was progressing toward failure and

should have alerted FIGG Bridge Engineers and MCM to the origin of the distress mechanism that was

causing the cracking and the rapidity of cracking progression.

16. Louis Berger was not quali�ed by the Florida Department of Transportation to conduct an independent

peer review and failed to perform an adequate review of the FIGG Bridge Engineers design plans and to

recognize the signi�cant under-design of the steel reinforcement within the 11/12 node, which was unable

to resist the horizontal shear between diagonal 11 and the bridge deck.

17. FIGG Bridge Engineers’ failure to adhere to the Florida Department of Transportation Plans

Preparation Manual requirements for a complex category 2 bridge structure within its work proposal to

MCM, calling for an independent �rm to conduct a comprehensive peer review, led to the inadequate peer

review performed by Louis Berger, which failed to detect the under-design of the bridge.

18. Had the Florida Department of Transportation Plans Preparation Manual called for all nodal forces of

category 2 bridge structures to be checked and veri�ed by a quali�ed independent peer review, this

collapse might have been prevented.

19. As part of its oversight of local agency program projects and new construction, the Florida Department

of Transportation should have veri�ed Louis Berger’s quali�cations as an independent peer review �rm for

complex bridge design–concrete upon receiving the 100 percent certi�cation letters for the bridge

foundation, substructure, and superstructure plans.

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20. FIGG Bridge Engineers did not perform its due diligence when it contracted with Louis Berger for the

independent peer review of the highly complex and uncommon concrete bridge design.

21. The restressing of member 11 was a manipulation of loads that constituted a change to the FIGG Bridge

Engineers design, and, before being implemented, should have been independently peer reviewed and

signed and sealed by a professional engineer.

22. The structural cracking and northward dislocation of the upper part of the member 11/12 nodal region,

as documented in the days leading up to the collapse, was strong evidence that the structure was

progressing toward failure; and the detensioning of the 5 post-tensioning rods located in member 11

signi�cantly increased the damage to the member 11/12 nodal region.

23. Although the FIGG Bridge Engineers engineer of record and design manager were engaged by MCM to

assess the increased cracking of the structure, they neither recognized that the singular load path in this

nonredundant bridge had been compromised nor took appropriate action to mitigate the risk of failure.

24. Beginning with the cracking identi�ed on February 24, 2018, the distress in the main span structure

was active, continued to grow, and was well documented by all parties involved in the design, construction,

and oversight of the bridge.

25. Neither Florida International University, MCM, FIGG Bridge Engineers, nor Bolton, Perez and

Associates Consulting Engineers took the responsibility for declaring that the cracks were beyond any level

of acceptability and did not meet Florida Department of Transportation standards.

26. Under the terms and conditions of the contract, Bolton, Perez and Associates Consulting Engineers had

the authority to direct or authorize partial or complete road closures as necessary, acting in concert with

the Florida Department of Transportation and Florida International University; however, none acted to

close the road under the bridge, contributing to the severity of the impact of the bridge collapse.

27. Local agency program agreements require stronger language to clarify that the certi�ed local agency

has the authority to immediately close a bridge when structural cracks are �rst detected or in situations

that require further investigation to protect the health, safety, and welfare of the public.

28. Given the pedestrian bridge’s unique, nonredundant design, the Florida Department of Transportation

should have ensured that the local agencies involved in the project had adequate staff who were trained

and experienced in administering these types of uncommon bridge designs.

29. The Florida Department of Transportation should have provided greater oversight of this complex local

agency program project to ensure that all safety issues were identi�ed and addressed.

30. Given the serious consequences of the error made by FIGG Bridge Engineers in assuming that the

bridge had a redundant design, when it did not, and the current lack of guidance concerning redundancy

design in concrete and pedestrian bridges, design speci�cation publications for concrete and pedestrian

bridges should be revised to include redundancy guidance.

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Scott Judy is Deputy Editor for Regions, and editor of ENR Southeast, one of Engineering News-Record's 10 Regional publications. His roughly 27 years as a construction journalist began with an 11-year stint covering Midwest construction projects. In 2000, Judy helped launch the publication now known as ENR Southeast. He often delves into controversial aspects of the construction industry such as bankruptcies and fatal accidents, and wishes he would never have to cover another accident but suspects that he might.

Tom Ichniowski has been writing about the federal government as ENR’s Washington Bureau Chief since the George H.W. Bush administration, and he has covered at least �ve major highway bills. A recognized expert on government policy on infrastructure and regulation, Tom is also a Baltimore native and Orioles fan who grew up rooting for Brooks and Frank Robinson. He is a graduate of Columbia College and Columbia’s graduate school of journalism, where he once used “unrelentless” in a headline.