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Term 3, 2020 CVEN9723 DESIGN OF CONSTRUCTION OPERATIONS

Instructor: Dr X Shen

Date: 22 September 2020

Building Estimating

Revanth

Learning Objectives • How to estimate the cost for building foundations? • What is work breakdown structure (WBS)?

Shoring Systems

Shoring in construction involves the process of supporting a structure in order to prevent collapse so that construction can proceed Two core components:

– Horizontal shores or struts – Temporary vertical wall system

Types of Shoring Systems

• Timber Shoring • Aluminium Hydraulic Shoring • Lagging • Sheet Piling

(Courtesy: Shoringsolutios)

Timber Shoring

• Vertical timber uprights provide supports against the sides of the excavation • Uprights are supported by horizontal beams called wales or stringers • Wales are supported by horizontal timber cross-braces or struts • When continuous uprights are used, this shoring system is called timber sheeting

Timber Shoring

(Courtesy: Roadplates & Nunnally 2011)

Example 1 Estimate the cost of installing and removing shoring system for a trench 100 ft long and 7 ft deep. The sheeting will be 2 x 12-in lumber, 8 ft long. Two horizontal rows of 4 x 6-in wales will be placed on each side of the trench for the full length of the trench. Trench braces will be placed 4 ft apart along each row of wales. The sheeting will be driven one plank at a time by using an air compressor and a pneumatic hammer. Two labourers combined will install the sheeting at 4/hr and wales and braces at 3/hr. The following material cost will apply: sheeting $0.73/bf, wales $0.92/bf and braces $3.50 each. The following equipment cost will apply: air compressor $8.75/hr and air hammer $1.75/hr. Labour costs are $21.67/hr for driving sheet piles and $18.17 for installing wales and braces.

Pile Foundations

Classifications of Piles – Load bearing: used for supporting deep

foundations – Sheet piling: used to support and/or retain

earth

Types of Load-bearing Piles

• Timber Piles • Concrete Piles

– Precast concrete piles – Cast-in-place concrete piles

• Steel Piles – H section – Steel pipe

• Composite Piles

Types of Load-bearing Piles

Steel Piles • Used for drive piles through considerable depths of poor soil to reach solid rock or another formation having high load-bearing properties • A cap can be installed on the top of piles to reduce the potential for damage during the driving operation

(Courtesy: Haywardbaker)

Steel Piles

Approximate number of steel piles driven to full penetration per hour

Example 2 Estimate the cost of furnishing and driving 180 steel piles, 40 ft long. The piles weigh 73 lbs/ft and are driven to full penetration into soil having high frictional resistance. A foreman with one crane operator and three labourers will be on the job. The following cost information will apply: piles = $0.32/lb., pile caps = $87.00., crane = $82.40/hr., leads for hammer = $14.63/hr., hammer = $10.80/hr., air compressor = $14.65/hr., other equipment and supplies = $9.35/hr., foreman = $25.00/hr., crane operator = $21.67/hr., and general labourers = $15.56/hr. Actual working time will be 45 min in one hour.

Detailed Estimates • Prepared when project specific quantities are developed and project execution options are clarified • Detailed estimates are based on the application of semi-detailed or detailed unit costs to these project specific quantities • In addition to quantity/unit cost items, a detailed estimate will also include various lump sum items and allowances or provisions.

Detailed Estimates Variables impacting reliability and accuracy of detailed estimates

– Level of scope definition; – A sound execution plan; – Knowledge of site conditions; – Level of review; – Benchmark data for the review process; – Time to prepare the estimate.

Work Breakdown Structure (WBS)

• WBS is one of the principal tools for planning and controlling the work content of projects in terms of its products (deliverables) and activities. • The WBS breaks the work down into packages and tasks for the purposes of organising the work. • A WBS is commonly developed at the beginning of a project, and is used for defining project scope, planning work activities and estimating costs. It lives on, throughout the project.

Work Breakdown Structure (WBS)

• Detailed estimate items are grouped together using the project WBS • The estimator needs to review the WBS to ensure it reflects the current scope, and includes all items of cost that may be needed, such as “Owners” and other indirect type costs. • A typical WBS should cover all the direct field cost physical areas and then make provision for field or site indirect costs, off-site indirect costs, and other project costs.

Work Breakdown Structure (WBS)

High Level Sample WBS for Mining Construction

Start-of-the-art Tools for Estimating

• Building Information Modelling (BIM)

Learning Objectives • How to estimate the cost for building foundations? • What is work breakdown structure (WBS)?

Questions?