Effects of Temperature Variations on Structural Vibration Properties

Modal parameters are subjected to significant changes not only by damage, but also by environmental conditions. Without quantifying environmental effects, applying vibration-based damage detection techniques may result in false damage identification. Collecting vibration and temperature data continuously have enabled researchers to investigate the correlation between environmental effects and identified modal parameters. Amid different environmental effects, temperature variations have been found to have the biggest impact on vibrational characteristics of bridges. In this paper, the effect of temperature on vibrational characteristics of a continuously monitored bridge, located in Perry, Utah, is presented. This bridge is instrumented with a monitoring system that collects vibration and temperature data at different locations of the bridge every hour. For dimensionality reduction, principle components of temperature measurements were extracted by applying principle component analysis (PCA). Natural frequencies of the structure are identified from ambient vibration data using the natural excitation technique (NExT) along with the Eigen system realization (ERA) algorithm. Variability of identified natural frequencies were investigated based on statistical properties of identified frequencies. A nonlinear ARX model and nonlinear polynomial models were used to find the relationship between the measured temperature and natural frequencies. The nonlinear ARX model showed natural frequencies are dependent to previously measured temperatures. This model was validated by using different sets of available data. These two models were evaluated and compared based on the statistical properties.