Base isolation for near-fault motions

Three analytical studies of base-isolated structures are carried out. First . six pairs of near-fault motions oriented in directions parallel and norma l to the fault were considered, and the average of the response spectra of these earthquake records was obtained. This study shows that in addition to pulse-type displacements, these motions contain significant energy at high frequencies and that the real and pseudo-velocity spectra are quite differ ent. The second analysis modelled the response of a model of an isolated structu re with a flexible superstructure to study the effect of isolation damping on the performance of different isolation systems under near-fault motion. The results show that there exists a value of isolation system damping for which the superstructure acceleration for a given structural system attains a minimum value under near-fault motion. Therefore, although increasing th e bearing damping beyond a certain value may decrease the bearing displacem ent, it may transmit higher accelerations into the superstructure. Finally, the behaviour of four isolation systems subjected to the normal co mponent of each of the near-fault motions were studied, showing that EDF ty pe isolation systems may be the optimum choice for the design of isolated s tructures in near-fault locations. Copyright (C) 2001 John Wiley & Sons, Lt d.