Determining individual member stiffness of bridge structures using a simple dynamic procedure

A reliable determination of the structural condition of timber bridges presently requires costly load testing. A new dynamic based testing method was developed by authors to reduce the cost and shorten the testing time. The method has been successfully used to undertake field-testing of more than 40 timber bridges across NSW. The dynamic testing procedure involves the attachment of accelerometers underneath the bridge girders. The bridge girders are then excited by a modal hammer. The method requires tests with and without extra mass, so that the overall flexural stiffness of the bridge can be obtained. However, in order to accurately estimate the load carrying capacity of the bridge, it is necessary to obtain the stiffness values of individual members from test results without complicating the current testing procedure. In this paper, the authors review the dynamic testing procedure and propose a method to determine individual member stiffness for a bridge structure based on the field dynamic testing data. The outcomes of this work not only enable more accurate prediction of the load carrying capacity of the bridge but will also identify defective members of the bridge structure.