Investigation of the modal frequency of a long-span suspension bridge under multiple environmental conditions

This study employs advanced techniques, namely the improved multi-synchrosqueezing transform (IMSST ) and the Fourier synchrosqueezed transform (FSST ), to extract the instantaneous frequency of the Humber Bridge, in the UK, in operational conditions. First, a brief overview of the relevant theories behind the techniques used is provided. These techniques are then applied to track the instantaneous frequencies within the monitored vertical acceleration data of the bridge. The instantaneous frequencies extracted by both techniques are verified against each other. The investigation further encompasses the development of three distinct regression models: a simple regression model, an expanded regression model and a regression model based on principal component analysis (PCA). The efficacy of the PCA-based model is scrutinised by generating and testing datasets that mirror the monitored data, with the Kolmogorov-Smirnov (KS) test confirming their validity. The findings of this research indicate a statistically significant inverse relationship between modal frequency and acceleration intensity. Furthermore, by incorporating wind effect considerations into the regression analysis, the R-squared values in both the expanded and PCA-based models exhibit substantial improvements. This demonstrates the performance of the enhanced model in capturing the dynamics of the bridge. The robustness of the PCA-based model is further corroborated by its performance during testing, proving its potential as a reliable tool in structural health monitoring (SHM).