A cost effective approach for integrity assessment of timber bridges

To develop a reliable and cost effective tool to assess the structural integrity of aged timber bridges is currently a challenge facing structural engineers. Whilst proof-load testing and Non-destructive Evaluation (NDE) techniques provide valuable assessment, such procedures are generally too complex, costly and time consuming to be applied across the entire inventory of timber bridges. A simple dynamic based testing method was developed by authors to lower the cost and shorten the testing time. The method has recently been used successfully to undertake field-testing of more than 180 timber bridges across NSW. This paper summarises the analytical development of this new approach together with some experimental examples. In the analytical studies, a closed form solution was obtained to provide an explicit relationship between the flexural stiffness and measured modal parameters. A beam with spring and masses attached was used to model a bridge with added mass or alternative added mass such as a trailer and/or a water tank for bridge testing. After obtaining the in-service stiffness of the tested bridge, a probabilistic modelling based on bending strength and gross stiffness (EI) of timber girders, is developed to provide an assessment of bridge load carrying capacity by using predicted in-service stiffness. Results of experimental studies and field testing using this approach are given in the references.