Performance of variable friction pendulum system for torsionally coupled structures

Abstract

A method for dynamic analysis of a torsionally coupled structure isolated with variable friction pendulum system (VFPS) (an advanced friction base isolator recently developed by the authors) is demonstrated. As the name suggests, the novelty of the VFPS is its variation of the friction coefficient at the sliding interface. The friction coefficient of the VFPS is such that up to a certain value of the isolator displacement it increases and then it decreases with a further increase in the isolator displacement. Six pairs of near-fault ground motions are selected as input ground motions in the study. The analysis considers the effects of the interaction developed between the frictional forces in the two principal directions due to sliding of the individual VFPS isolator. In order to investigate the effectiveness of the base isolation using the VFPS, the coupled lateral-torsional response is obtained under different parametric variations by employing Newmark's step-by-step method assuming linear variation of acceleration over a small time interval. The effectiveness of the base isolation using the VFPS is quantified with the help of the response ratio between the peak responses of the torsionally coupled structure with and without the VFPS. Moreover, the behavior of the structure isolated by the VFPS has been compared with the same structure isolated using the conventional friction pendulum system (FPS) and the double concave friction pendulum (DCFP) bearing. The numerical results of the extensive parametric study help in understanding the torsional behavior of the structure isolated with the VFPS under near-fault ground motions. It is also found that the VFPS behaves remarkably better than the FPS in controlling the torsional response for all types of torsional systems. The VFPS is also superior to the DCFP for torsionally flexible systems, whereas the behavior of the VFPS is nearly identical to that of the DCFP for torsionally rigid systems.