Seismic Fragility Assessment of Steel Structures Supported on Friction Pendulum Isolators Subjected to Far-Field Ground Motions

Abstract

In this paper, attempts are made to compare the seismic fragility and the probability of failure of steel structures supported on different types of friction pendulum isolators. These isolators including single friction, dual friction pendulum and triple friction pendulum are designed to have similar effective periods as a prominent characteristic of them. The designed bearings have 3- to 5-second effective period and supports 3- and 6-story moment framed steel structures. These two superstructures represent short-range and intermediate-order buildings based on HAZUS technical manual. Three-dimensional nonlinear models of the structures are idealized in a finite element framework and nonlinear time history analyses are performed. In order to compute the fragility of the structure, the probable uncertainty sources in an isolated building such as earthquake record, modeling, design, and properties of materials in a probabilistic framework are considered. Furthermore, incremental dynamic analysis (IDA) is performed and the fragility curves of the structure are obtained in slight, moderate, extensive and collapse damage states (DS). Calculating the failure probability according to FEMA P-695, it is showed that all the isolated structures have less than 10% collapse probability. In addition, it is revealed that the triple concave friction pendulum (TCFP) has greater collapse margin ratio (CMR) than other kind of friction bearings. Growing the effective period of TCFP from 3 to 5 seconds, increases the CMR nearly 70 percent.

Keywords

• friction pendulum isolator
• seismic fragility
• damage state
• incremental dynamic analysis
• performance based design