Towards Predictability of Bridge Health

Any assessment document pertaining to existing bridge infrastructure requires an accurate record of each individual bridge in service, the history of repairs and modification as well as the current state of structural health after each inspection. Bridge inspections need not only be regularly documented, but compared with previous inspections and the probability of ongoing performance assessed. Such knowledge allows the planning of regional sustainability of rural bridges over major and minor transport corridors. This paper examines the variety of timber bridges on rural NSW roads with the data that describe the likely limitations to normal loading. The discussion outlines the level of measurement accuracy required for documenting bridge health and experimental evidence verifying the level of accuracy achievable. Because many timber bridges have had a variety of owners, and society has for many years restricted the funds available for infrastructure maintenance, bridge structural health is poorly understood at any level of quantifiable predictability. Alternative methods of monitoring heavy traffic on rural roads have not been well examined and bridge load limits may often not reflect actual bridge carrying capacity. In the absence of suitable data, some of the structures being replaced may not be the ones at most risk of failure. This is not a new issue and has changed little in the last twenty years. To extend the serviceable life of bridges and to sustain a low probability of structural failure, new low cost measurement systems are required. This paper discusses one such method of measuring mid-span deflection that can be readily used by bridge maintenance crews after short periods of training.