Regional Timber Bridge Girder Reliability: Structural Health Monitoring and Reliability Strategies

Many short span timber beam bridges in regional New South Wales are of unknown reliability, have high traffic loadings and were designed according to codes, many of which have since been superseded. Because asset managers are delaying their maintenance for fiscal reasons, a high proportion of these bridges are structurally degraded and potentially unsafe when excessively loaded. In regional areas, a prioritised maintenance program can be a cost effective alternative to bridge replacement. Such older bridges will require continuous monitoring by low cost methods to assess the temporal probability of their failure. This paper examines the potential for measuring the mid-span deflections of girders caused by high traffic loads to obtain continually updated indicators of the structural health of girders. The mid-span deflection data of a case study bridge were continuously measured using a laser based measuring system, recently developed by the first author. An analysis of the deflection data is used to obtain a reliability index and the probability of bridge failure. Reliability indicators such as these can be used, in conjunction with continuous deflection monitoring, to prioritise cost effective maintenance of older timber bridges in regional New South Wales.