Strength reduction factor spectra of self-centering SDOF systems with flag-shaped model subjected to offshore ground motions

Offshore structures pose greater challenges for post-earthquake repairs compared to onshore structures. To enhance seismic resilience, offshore structures can be designed as self-centering structures. In order to study the seismic performance of offshore self-centering structures, this paper selects 384 offshore and onshore ground motions from the K-NET database to calculate the strength reduction factor spectra of self-centering Single Degree of Freedom (SDOF) systems and analyze their influence factors. The analysis begins by examining the influence of ductility factor (mu), post-yield stiffness ratio (alpha), and hysteretic energy dissipation ratio (beta) on the strength reduction factor spectra. Furthermore, differences in these spectra under offshore and onshore ground motions, as well as between long-period and ordinary ground motions, are analyzed. Secondly, the study investigates the influence of earthquake magnitude, epicentral distance, site conditions, and source type on the strength reduction factor spectra. Finally, an artificial neural network is employed to fit the strength reduction factor spectra of the self-centering structure. The analysis results reveal the significant disparities in the strength reduction factor spectra of self-centering structures between offshore and onshore ground motions. Therefore, in the seismic design of offshore self-centering structures, particular attention must be given to the influence of offshore ground motions, especially for long-period. In addition, comprehensive consideration of site conditions, source type, moment magnitude, and epicentral distance is essential to ensure the safety of the structure.