CIVIL ENGINEERING 365 ALL ABOUT CIVIL ENGINEERING



AbstractNumerous bridges in the mountainous areas of southwest China are constructed with tall reinforced-concrete (RC) piers. This paper presents the influence of higher-mode effects of pier columns on seismic performance in a quantitative manner for, to our knowledge, the first time, while the impact of excitation intensity and the frequency content of input motion, which do not appear to be considered in any previous study, are incorporated as well. Numerical models are developed for three bridges with different pier heights, considering higher-mode effects by comparing the seismic responses computed from multi-degree-of-freedom and single-degree-of-freedom systems. An incremental dynamic analysis method is used to investigate the influence of input intensity, and motions matching different target spectra are employed, showing the effects of frequency components. The analytical results show that when the tall piers remain elastic or experience substantial nonlinearity approaching the ultimate state, the higher-order modes contribute more significantly to the seismic responses, while input excitations with more low-frequency components could generally suppress the effects of higher-order modes. Based on the analysis, seismic design strategies for tall piers are discussed and a novel design scheme using preset plastic region length is proposed, which is demonstrated to be able to limit the range of damage with a negligible increase in maximum curvature demand.



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