Constructing input to neural networks for modeling temperature-caused modal variability: Mean temperatures, effective temperatures, and principal components of temperatures

In this study, the construction of appropriate input to neural networks for modeling the temperature-caused modal variability is addressed with intent to enhance the reproduction and prediction capabilities of the formulated correlation models. Available for this study are 770 h modal frequency and temperature data that were obtained from the instrumented cable-stayed Ting Kau Bridge in Hong Kong. With the temperature data measured at different portions of the bridge, three kinds of input, i.e., mean temperatures, effective temperatures, and principal components (PCs) of temperatures, are constructed as input to neural networks for modeling the correlation between the modal frequencies and environmental temperatures. By dividing the 770 h modal frequency and temperature data into training data set, validation data set and testing data set, an optimally configured back-propagation neural network (BPNN) is formulated for each kind of input, in which the validation data are utilized to determine the optimal number of hidden nodes while the early stopping technique is applied to optimize the BPNN parameters. Then the reproduction and prediction performance of the BPNNs configured with the three kinds of input is examined and compared in respect of the seen training data set and the unseen testing data set, respectively. It is revealed that the temperature profile characterized by the effective temperatures is insufficient for formulating a good correlation model between the modal frequencies and temperatures. When a sufficient number of PCs are used, the BPNN with input of the PCs of temperatures performs better than the BPNN with input of the mean temperatures in both reproduction and prediction capabilities.