Bridges

Australia is home to many greatly loved and historic bridges. The lift bridge over the Murray River at Swan Hill (1896) and the Whipple truss bridge over the Shoalhaven River at Nowra (1881) are two such bridges. Preservation of these bridges should be considered even if newer bridges replace their current function. It is essential to make informed and defendable decisions when considering any repairs, strengthening works and their viability for repurposing as pedestrian or shared use bridges. Engineers working on such bridges must therefore obtain a good understanding of deterioration mechanisms and structural behaviour. This is not a straightforward exercise when dealing with older materials and limited design and construction records. This paper uses the Swan Hill and Nowra Bridges to demonstrate the investigation, analysis, design and repair techniques to support this process. Both bridges are supported on cast iron piers with mass concrete infill. The cast iron piles exhibit loss of section due to graphitisation and have vertical cracks in some segments. This paper details the modelling techniques used to determine the capacities of the piles in their current condition as well as post-remediation. One of the analytical challenges included the interaction between the cracked cast iron segments, the mass concrete infill, and the grouted remedial banding. The analysis provides insights into the probable causes of the vertical cracks. Reinstating hoop tensile strength through remediation presents many challenges which are discussed in this paper. The installation of grouted bands, which was the chosen remedial method, also presented difficulties which were overcome with appropriate detailing. The cracks continue to be monitored and the piers are performing satisfactorily to date. The remediation has allowed both bridges to continue serving the community for many years to come.