Bridges

Recent major projects in Victoria and elsewhere have adopted steel trough girders. With a high torsional stiffness, this bridge type offers design flexibility for curved alignments and longer spans, and construction speed by permitting erection by crane or SPMT of entire spans. However, there are also challenges for construction engineering that need to be addressed to mitigate project risks.

To suit road design geometry trough girders can be curved, typically with several girders running parallel to each other to form one composite superstructure via the reinforced concrete deck. For construction and logistics, these girders are fabricated in smaller sections, transported on trailers and lifted by crane. They can be landed on temporary jacks but due to girder curvature and narrow soffit, they are not intrinsically stable and need propping to mitigate the risk of overturning before permanent cross-bracing between the girders is installed. As the girders are progressively installed deflected shape changes at each stage and therefore these staged deflections need to be understood to ensure bolted connections “fit up” during erection. Detailed analysis of the geometry of the girders, while suspended from the crane, can be used to assess clearances and to ensure fit-up during bolting in the air to complete the splice connections so that the crane can be released without delay.

There is an important interface between the fabrication team and the construction engineering team to ensure the right geometry is achieved at the right time in the construction sequence. Another important interface is between temporary and permanent work designers, with early interaction providing the best opportunity for design optimisation.

While some temporary works are required to ensure stability, they can be optimised to make the best use of existing permanent works. An example is presented by making dual use of existing girder connections rather than introducing additional welded single-use temporary attachments into the permanent works.

This paper highlights some key technical challenges and lessons learnt from the construction of this bridge type.