Interstory drift based scaling of earthquake ground motions

A novel amplitude scaling procedure is proposed in this study where the ground motion scaling factors are defined as the ratio of interstory drift distributions under target spectrum versus under the associated ground motion spectrum. The advantage of employing interstory drift ratio in ground motion scaling, compared to employing spectral intensity directly, is that it provides a strong theoretical link between the target spectrum intensity and the fundamental dynamic characteristics of the structure. Hence, scaling is conditioned on structural response, which is in turn a function of seismic intensity. The interstory drift-based scaling procedure (IDS) is presented herein for planar frames for brevity. Accuracy and efficiency of the IDS procedure is assessed under a set of near fault strong motions from large magnitude events. The results revealed that the proposed procedure is accurate since the resulting bias in estimating linear elastic interstory drifts is negligibly small. Further, it is noticeably more effective as compared to the conventional procedures suggested in recent seismic codes, yet it is simpler.