Study on the influence of initial pulse action characteristics for near-field long-period ground motion on the seismic performance of RC columns

Due to the influence of velocity pulses, the elastic-plastic displacement time history response of structures under near-field long-period ground motions (NLGM) are different from those under ordinary ground motions (OGM). To investigate the impact of NLGM on structural performance, it is essential to clarify the mechanism by which the unique characteristics of NLGM affect the seismic behavior of structural components. In this study, a quasi-static loading protocols that reflects the action characteristics of NLGM was used for quasi-static testing and numerical simulation Subsequently, the influence of NLGM characteristics on the seismic performance of reinforced concrete (RC) columns was studied through quasi-static tests and finite element analysis with different loading protocols and design parameters, revealing the preliminary impact of NLGM action characteristics on RC columns. The results indicate that NLGM has significant initial pulse characteristics, and the initial pulse amplitude can be used as an indicator of the action characteristics of NLGM; The initial pulse significantly affects the strength, stiffness degradation, energy dissipation, and deformation performance of the specimens, and the influence of pulse amplitude varies under different design parameters. A higher initial pulse amplitude tends to cause the structure to enter the plastic stage earlier and results in a larger residual displacement ratio. The early damage caused by the initial pulse has a decisive impact on the later response of the specimens. Finally, based on the analysis results, a calculation model for the reduction coefficientof seismic performance indicators considering the initial pulse action characteristics of NLGM was proposed.