Developing a simplified method for analysis and design of isolated structures with the novel quintuple friction pendulum system under bidirectional near-field excitations

Simplified analysis methods for seismically isolated structures proposed in recent structural codes and specifications are frequently used to reduce the computational effort and to simplify the design procedure, either directly for special cases or for checking the results of nonlinear response history analysis. Of the approximate methods, the equivalent lateral force procedure using the effective stiffness and effective damping is one of the best known. In this study, the simplified method is developed by combining the equivalent lateral force procedure with the capacity spectrum method and evaluated in terms of maximum isolator displacements and base shears for isolated structures with recently invented quintuple friction pendulum isolators , with different geometrical and frictional properties, under two different response spectra with corresponding two different sets of bidirectional near-field ground motions for stiff and soft soils site classes. In order to assess the accuracy of the simplified method, the delivered results of the ELF procedure are compared to those of nonlinear response history analysis, by modelling the quintuple friction pendulum isolator 3D element in OpenSees. Eventually, comments on the accuracy of the simplified method are given to make its applications more appropriate in practical design of base isolation systems.