Bridges

In today's infrastructure industry, constructability and cost-efficiency of structures are increasingly crucial in engineering design. When developing concepts for large-span bridges, it is essential to consider the impacts of constructability when seeking to strike a balance between aesthetics, engineering efficiency, and cost. For a pedestrian bridge requiring a minimum span of 98 meters over water (or road), related activities such as temporary works and erection methodology have the largest impact on cost and community.

To minimise site and community impacts, as well as overall costs associated with steel usage and craneage, a lightweight steel truss girder was selected for the new Birtinya Pedestrian Bridge over Lake Kawana. This resulted in a comparatively light structure which, whilst advantageous for construction impacts, necessitated a more detailed dynamic analysis to ensure pedestrian traffic did not experience uncomfortable vibrations. Several key considerations of the bridge, such as choice of stay type (bar or cable), stressing sequence, foundations and the length of truss girders were determined based on constructability and durability requirements.

Whilst Design Engineers can devise construction methodologies that will be structurally ideal for the behaviour of the bridge, Contractors can provide invaluable input regarding construction methodologies from previous experience and consideration of issues associated with product procurement and available construction plant. Material savings from the ideal construction methodology proposed by the designer can often pale in comparison to the cost and program savings associated with contractor-preferred construction methodologies.

Multiple International Standards provide guidance on pedestrian dynamic analysis and should be sought for guidance. The UK National Annex to Eurocode, HIVOSS, and SETRA provide reasonable approaches to assessing dynamic responses of structures and generally apply similar equations and limits.