Monitoring timber beam bridge structural reliability in regional Australia

There are many thousands of timber beam bridges throughout regional Australia, which are monitored primarily by visual inspection. Experience gained from historical failures has led to the clear realisation that visual inspection at intervals of many months or years is insufficient to identify potential failure caused by overloading and biological degradation. A bridge overloaded today can fail tomorrow and there is a need to implement structural health monitoring (SHM) so that the incidence of overloading can be identified soon after it occurs. This need is becoming more vital with the increased expectation to cater for the increased loads during periods of transporting seasonal produce. The measurement mid-span displacement of girders can be used to determine safety indices for the evaluation of structural safety. The detection of real-time damage in timber girder bridges by the use of high-speed camera and laser-based methods offer unique advantages and can lead to low cost measurement techniques. This work reports on the use of continuous monitoring methods for determining the structural reliability of timber-beam bridge girders. Some applications of the use of laser-based displacement sensing systems are discussed in relation to the monitoring of the structural reliability of two older timber beam bridges in regional New South Wales, Australia. Experimental and analytical approaches are presented and used to demonstrate that the probability of failure can be readily determined on a continuous basis using an SHM system.