Bridges

The Kempsey Bridge, built in 1960, is a steel truss bridge spanning the Macleay River at Kempsey on the Pacific Highway (SH10). The 279.57 m long bridge consists of twelve spans, including four 47 m truss spans. These trusses incorporate seven steel cross girders and six stringers supporting a 178 mm thick concrete deck. The carriageway width is approximately 7.11 m between kerbs, accommodating two lanes of traffic with an Average Annual Daily Traffic (AADT) of approximately 20,000 vehicles. A 1.37 m width footpath is located on the downstream side.

Bridges constructed during this period commonly utilised a coped-end detail for connecting girders to cross girders. This design is prone to fatigue-induced cracking, which can become a safety critical issue. Close up inspections identified cracking at the welds between the end plate and the web of the stringers in multiple locations. The cracks were monitored regularly, and various repair solutions were proposed and trialled. However, none of the repair approaches trialled proved entirely satisfactory.

A research project was undertaken in collaboration with the University of Sydney, involving full-scale instrumentation and advanced finite element analysis to develop a solution from first principles. The approach addressed both global and local solutions to mitigate the issue. An innovative solution using independent brackets was devised to create a new load path without requiring in-situ weld repairs.
Several challenges were encountered in implementing this solution, including the need for extremely tight tolerances to fit brackets precisely in over 168 locations of each span on the existing bridge. 3D scanning was employed to ensure a perfect fit for all components.

This paper discusses the development of the innovative solution based on research, full scale instrumentation, and advanced analysis. The solution has the potential to benefit similar bridges across the state, where no satisfactory resolution has yet been found.