Life-cycle seismic performance of bridges with thin-walled steel piers under bi-directional excitations

In corrosive environments, steel bridges demonstrate time-dependent seismic performance and varied directional responses to bi-directional excitation at different life-cycle stages. However, current seismic assessment methods for bridges have not adequately addressed the time-dependent effects of bi-directional excitation directionality on seismic responses throughout their entire life cycle. Thus, this study aims to investigate the time-varying directional effects of bi-directional seismic excitations on steel bridges with multiple parameters and to propose a method for predicting the range of critical incident angles while considering the aging effects of bridges. Initially, time-dependent functions that characterize steel corrosion are integrated into multiscale finite element models of the steel bridges to simulate corrosion progression across their life-cycle stages. Subsequently, a quantitative analysis of the bi-directional seismic response of steel bridges is conducted throughout their life cycle, accounting for the directionality of seismic excitation. Finally, a method and process for predicting the range of time-varying bi-directional critical incident angles with 95 % probability are derived by fitting the statistical probability distribution boundary values of the critical incident angle deviation index. The study's findings indicate that the aging effects of steel bridges amplify the displacement response under bi-directional seismic excitation, with the maximum displacement response difference exceeds 40 %. The service time may increase the sensitivity of steel bridges to changes in incident angles, potentially amplifying the displacement response by a factor of 1.69. The study's findings highlight the importance of considering aging effects and bidirectional excitation directionality in bridge seismic assessments.