Vibration monitoring of bridges

Traditional visual inspection tools, which are typically carried out annually, can only detect obvious damages like disruption, cracks or rust on the surface of bridges. Advanced non-destructive and destructive inspection tools are usually applied when visual inspection can’t provide sufficient information. Besides these techniques engineering surveyors can conduct geometric deformation analysis that provides additional information for damage detection of structures. The implementation of appropriate methods for data acquisition and analysis to detect changes to the material, geometric and dynamic characteristics of structures is summarised under the term Structural Health Monitoring (SHM). The essential idea of SHM is to determine a normal behaviour of undamaged structures and to obtain qualitative conclusions from changes of this behaviour related to the current health status. Information about changes within the dynamic characteristics of structures can be detected by applying accelerometers, which are a component of Ambient Vibration Methods (AVM) as an integral part of SHM. Analysis of acceleration measurements can derive natural frequencies that depend on weight, material, stress and strain as well as the geometry of the object. Hence this data can be used to derive additional information about the capacity and condition of a structure. In this paper we present a measurement system based on low-cost accelerometers that nevertheless performs measurements with high accuracy. This autonomously operatable device features a memory card slot, an internal battery, a waterproof housing and temperature resistant components. Additionally real time data transfer can be obtained via wireless LAN or USB connection to a computer. All necessary steps of data acquisition, processing and interpretation of vibration monitoring will be presented on a practical example.