Long-term monitoring of vibration properties of structures with different materials and boundary conditions

Abstract

Different methods have been developed for structural conditions monitoring. Among them, vibration-based methods have been receiving a lot of attentions because any change in structural conditions will result in a change in structural vibration properties such as frequencies and mode shapes. Despite relatively straightforward theory that relates structural vibration properties to structural stiffness, not many successful stories of structural damage identifications have been reported in practice. This is because of many uncertainties in structural modelling and noises in vibration measurements that affect the reliability of vibration-based methods for structural condition monitoring. Changing environmental conditions such as temperature and humidity will cause changes in structural vibration properties. These changes might be more significant than the change caused by minor structural damage thus result in the vibration-based methods being ineffective in identifying the structural conditions. To overcome these problems, relations of changing environmental conditions and structural vibration properties should be quantified. This paper reports results from intensive laboratory tests of the influences of changing ambient environmental conditions on vibration properties of structures made of different materials and having different dimensions and boundary conditions. In each test, the ambient temperature and humidity were recorded. The changes of vibration properties of the tested structures with temperature and humidity are presented and discussed in this paper. The results can be used in structural health monitoring to eliminate the influence of changing environmental conditions.