Large coseismic displacements and tall buildings

Abstract

SUMMARYSeismic demands imposed on tall buildings are sensitive to long‐period ground motions. A source of these motions can be near‐fault effects: rupture directivity and fling step (large coseismic displacements). The potential adverse effects of near‐fault motions on structures have been attributed to rupture directivity in previous studies. However, the influence of large coseismic displacement on tall building seismic response has not been widely investigated. This study explores the influence of coseismic displacements on the nonlinear response of tall buildings. Several nonlinear time history analyses were performed to evaluate the response of a reinforced concrete tall building to coseismic displacements. The ground motions used for these analyses were recorded in the proximity of faults where large coseismic displacements have been observed. Recorded motions from the Landers earthquake (1992), Kocaeli earthquake (1999), Tohoku earthquake (2011) and Chi‐Chi earthquake (1999) were selected for this study. The results from a parametric study of the response of a single‐degree‐of‐freedom system showed that the influence of the fling on the system response is dependent on (a) the ratio of fling rise time to the fundamental period of the system and (b) the yielding resistance of the structure. At the onset of yielding, the fling step can further drive the system into very large displacements. The results from the case study indicate a significant increase on the seismic response of a tall building when the fling effect is included in the ground motions. This issue is a concern for tall buildings in regions where faults are not mapped to a great extent and near‐fault fling effect could be produced by a large magnitude earthquake. Copyright © 2011 John Wiley & Sons, Ltd.