Bridges

Reinforced Concrete (RC) bridges started to emerge in New South Wales (NSW) during the latter part of the nineteenth century. NSW Railways built the first RC arch bridge at Hilltop in circa 1898, for the Hilltop to Colo Vale deviation of the main southern train line. This RC arch structure spanned between two sandstone abutments and the span length is about 12 m, with a carriageway width of 6.1 m. The bridge is still in use though the below railway line is no longer in service.

Recently, a field load testing was conducted to establish its load-carrying capacity using a Test Truck, after installing demountable strain gauges and deflection gauges at critical locations in the RC arch and brick parapet walls. Series of load runs were performed by gradually increasing the load levels. After the load testing exercise, comprehensive Geo- Structural based Finite Element (FE) analysis was conducted, considering the stiffness contribution of the fill material as well.

Comparison study was carried out between the load testing results and the FE analysis. Excellent correlation was obtained in terms of elastic strain values and deflection values. The stiffness contribution of the brick parapet wall, in sharing the live loads, also established from this study. In the light of this comparison study, FE model verification and Ultimate Limit State (ULS) demand versus capacity assessment were conducted to load rate the bridge in its current condition.

This paper catalogues this comparison study and discusses, how field load testing coupled with advanced FE analysis can be an effective tool in load rating century old RC bridges. The paper also discusses the limitation of this approach and provide recommendations for future study.