Variation of structural vibration characteristics versus non-uniform temperature distribution

In vibration-based condition assessment exercises, it is necessary to discriminate the variation of structural properties due to environmental changes from those caused by structural damages. Some efforts have been made to correlate the structural vibration characteristics and the air temperature or temperatures at the structural surface. As the temperature of an entire structure is generally non-uniformly distributed, using the air temperature or surface temperatures alone may not sufficiently capture the relation between the structural responses and temperatures. The present paper aims to investigate the variation of the structural vibration characteristics versus the non-uniform temperature field of the structure. Thermodynamic models are employed to estimate the temperature at different components of the structure at different times. As the material mechanical properties are temperature dependent, the structure can be regarded as a composite structure consisting of elements with different Young’s moduli. Consequently, the natural frequencies of the structure can be calculated with the finite element method. The procedures are repeated for different times and thus variation of the frequencies with respect to time is obtained. A simply supported RC slab was constructed and used as a proof-of-concept example. The temperatures at different points of the slab were recorded continuously in one day, together with a series of forced modal testing to extract its modal properties. On the other hand, a finite element model was established to conduct a transient thermal analysis and estimate the temperature distribution of the slab, which shows a good agreement with the measurement counterpart. The temperature data at all components and thermal properties of the material were then inputted to the model to calculate the frequencies, which also matched the measured frequencies very well. Moreover, a good linear correlation between the natural frequencies measured and the structural temperatures other than the air temperature or surface temperatures is observed. The present study provides a new approach to quantifying the environmental effect on the structural vibration characteristics.