Reliability of Symmetric and Asymmetric Structures Mounted on TCFP Base Isolators Subjected to Near-Field Earthquakes

The reliability of structures isolated with Triple Concave Friction Pendulum (TCFP) bearings subjected to near-field earthquakes is investigated. An extensive study is conducted to reveal the effect of superstructure mass eccentricity on the probability of failure (Pf) as well as the reliability index (β) of the structure supported on TCFPs with different properties. Results of different investigations show that friction coefficient of frictional isolators depends on several parameters; therefore, it should be assumed as a random variable. In order to consider the uncertainty of earthquake records a group of 45 sets of near-fault ground motion is selected and its amplitude is scaled with a random variable calculated based upon seismic hazard curve in a specific location. The seismic performance of structures is studied through four damage states (DSs) namely slight, moderate, extensive, and complete structural damages. Two essential engineering demand parameters (EDP) (i.e., interstory drift and acceleration) are assumed as performance functions in reliability-based investigation. The First Order Reliability Method (FORM) analysis performed by Risk Tools (RT) program demonstrated that complete structural DS has lower Pf and larger β compared to slight or moderate DS. Additionally, 30% of mass eccentricity has reduced the β to 23% in a six-story superstructure mounted on a 4-second-period isolator.