Case study : structural health monitoring of timber bridges using dynamic frequency analysis (DFA)

![CDATA[Australia has numerous ageing timber bridges in service. The structural efficiency of the majority of them have been impaired over time and their capacity is not known. There is, therefore, a critical need to develop new methods that will enable the load carrying capacity of these bridges to be estimated. In this paper, an established testing method known as Dynamic Frequency Analysis (DFA) and its application for monitoring of bridges is described throughout a case study (Mongarlowe Bridge). The testing procedure involves the attachment of sensors (accelerometers) underneath the bridge. The natural frequency and vibration response of the bridge superstructure is measured when a “calibrated sledgehammer” is used to excite the unloaded deck, and again with a relatively small mass applied at mid-span. The difference in response allows load carrying capacity of the bridge to be estimated. Furthermore, by regular monitoring of the bridge and its natural frequency, the potential degradation of the structure and the existing load bearing capacity can be determined.]]