Robust design optimization of the friction pendulum system isolated building considering system parameter uncertainties under seismic excitations

This paper presents a robust design optimization (RDO) of friction pendulum system (FPS) isolated building considering different uncertain parameters such as stiffness and damping ratio of the superstructure, stiffness and frictional force of the isolator and seismic excitation properties are considered as random parameters in this study. For this, the five-storey building is idealized using lumped mass considering FPS as the base isolator. Most analysis are carried out on the performance of FPS isolated structures assuming the system parameters to be deterministic. Neglecting parameters uncertainties can lead to underestimating the performance of FPS isolation system. Sensitivity analysis is carried out to determine the influence of each uncertain system parameters. Further, the optimal analysis is performed considering uncertainties to show the impact of the behaviour of FPS isolation system in which the optimization is performed using genetic algorithm considering root mean square acceleration (RMSA) as objective function. However, the optimal design involves minimizing the unconditional expected value of mean square response, without accounting for the uncertainties induced by the system parameters. In this regard, an RDO criterion for FPS base isolated building is performed in this study by considering various parameters uncertainty as random. The RDO process aims to reduce the combined value of the RMSA and its standard deviation for a given structure. The numerical study shows that the proposed RDO results yields significant improvements in terms of performance dispersion, accompanied by a marginal increase in RMSA response indicating its effectiveness over the unconditional response based optimum results.