Recent Question/Assignment

Design a Bridge

The Hume Highway is the main freight route between Sydney and Melbourne, and is a vital transport link for communities and industries in southern New South Wales. The original Sheahan Bridge over the Murrumbidgee River in Gundagai, which is a steel box girder bridge and was opened to traffic in March 1977, had a single lane in each traffic direction. To improve safety and traffic flow, the Roads and Maritime Services (RMS) NSW has duplicated the bridge immediately upstream. The new bridge was officially opened on 24 May 2009.
The new bridge comprises twenty-four spans of precast prestressed concrete T-beams (four in parallel) over the floodplain, and three spans of balanced cantilever box girder section over the river. The floodplain portion is 960 metres long so each T-beam is 40 metres long, which is among the longest in Australia.
Your tasks are to:

1. Propose an alternative conceptual designs and recommend why it satisfies the primary objectives of economy, feasibility and aesthetic elegance for the location.
2. Provide a “ball park” cost estimate for each alternative, show how you derive them.
3. Submit a scaled and fully dimensioned general arrangement drawing for your recommended alternative.
4. Provide calculations and sketches showing how you derive conceptual cross-section sizes for:
a. bridge girders, and
b. bridge piers or support towers.
For the purpose of determining the conceptual sizes, you only need to be concerned with the combination of dead and live loads only. Assume a factored live load on deck of 220 kN/m distributed over a 50 m discrete length. Concrete density is assumed to be 25 kN/m3, and steel 77 kN/m3.
Using the conceptual design dimensions, conduct a quantity survey and apply in-situ unit rates shown below to estimate the structure cost of your proposed bridge. Determine the construction cost estimate by multiplying the structure cost by 1.28 to include the costs of mobilisation and design, accessories and management. Use Rawlinsons Construction Cost Guide or Cordell Cost Guides to estimate your constructions costs, or assume the following
Bearing Piles $300/m

Bulk Excavation for Piles $30/m3
Backfill $150/m3
Formwork $150/m2
Concrete $300/m3
Reinforcing steel $2500/t

Structural steelwork $5000/t

To obtain the approximate tonnage of reinforcing steel, multiply the concrete volume (m3) by 0.12. More accurate estimates for particular parts of the bridge can be obtained from the Bridge Design Aids published by California Department of Transportation, which include

3. Safe construction sequence
Describe clearly the safe construction sequence proposed for your conceptual bridge, using illustrations. Your rationale needs to be substantiated with references that demonstrate the feasibility and safety of the proposed construction technique. Incorporate any applicable safety precautions.