Assessing the load carrying capacity of timber bridges using dynamic methods

Abstract

A reliable determination of the structural condition of timber bridges presently requires costly load testing. A new testing method is described which has recently been used to undertake field-testing of more than 20 timber bridges across NSW. The bridge assessment procedure involves the attachment of accelerometers underneath the bridge girders. The vibration response and natural frequency of the bridge superstructure is measured when a calibrated sledgehammer is used to hit the unloaded deck, and then again with a relatively small mass applied at mid-span. The difference in response allows load carrying capacity of the bridge to then be calculated.