MODELING ASPECTS OF STRUCTURES ISOLATED WITH THE FRICTIONAL PENDULUM SYSTEM

Different modelling aspects of structures isolated using the frictiona l pendulum system and subjected to earthquake ground motions are studi ed herein. Although the vertical dynamics of these structures is given special emphasis, other effects such as large isolator deformations a nd bidirectional input motion are also considered. Different structura l models of the FPS are developed and tested for single-storey structu res and a real four-storey building frame; among them, an 'exact' form ulation of the FPS force-deformation constitutive relationship is pres ented. Results show that global building responses can be computed wit hin 20 per cent error in the mean using a simplified model that ignore s the vertical motion of the building; however, structural member defo rmations and forces need to be computed using a model that considers s uch motion, This is of particular importance when there exist correlat ion between the horizontal and vertical components of ground motion. F urther, a physical model of the FPS is introduced and used to determin e the response of a real four-storey frame, including uplift and downw ard impact. Results from this analysis show that local column response s may vary substantially depending on the stiffness of the isolation s torey and the presence of a mass at the isolation level. Such mass is capable of filtering the large increase in column shear that results f rom the impact of the structure after uplift. Uplift occurs at several instants of the response of the structure considered, leading to an i ncrease in column base shear as large as 3 times the shear obtained by ignoring the vertical dynamics of the building. (C) 1998 John Wiley & Sons, Ltd.