Strong motion duration influence on nonlinear seismic response.

Abstract

The preferred representation of seismic hazard in structural design and assessment continues to be based on the elastic response spectrum. Even when dynamic time history analyses are required, the acceleration time histories used as input need to be compatible with the prescribed design spectrum. For infrastructure hosting nuclear related facilities, the criteria for developing these time histories is provided in Appendix F of the US NRC RG-1.208. While most of the criteria are devoted to quantifying the required level of matching, limitations on strong motion duration are rather vague and are limited to check that the spectrum-compatible series have durations consistent with characteristic values for the magnitude and distance of the controlling events defining the design spectrum. This work is aimed to investigate the level of influence that strong motion duration may have on the inelastic demand of reinforced concrete structures. Sets of short-duration spectrally-equivalent records are generated using as target the response spectrum of an actual long duration record. The sets of short duration records are applied to the numerical model of the structure along with the target long duration records in an incremental dynamic analysis approach so that the effect at different levels of inelastic demand can be investigated. Overall, it was found that long duration records tend to impose larger inelastic demands. However, such influence is difficult to quantify as it was found to depend on the dynamic properties of the structure, the strength and stiffness degrading characteristics, the approach used to generate the numerical model and the seismic scenario (target spectrum).