Behaviour of Triple Friction Pendulum isolator under forward directivity and fling step effect

Abstract

The Triple Friction Pendulum (TFP) bearing consists of two facing concave steel surfaces separated by an internal nested assembly of two facing concave surfaces separated by an articulated slider. In spite of being fully passive device, TFP bearing exhibits adaptive behavior under different hazard level of earthquakes owing to multiple sliding surfaces. The paper describes response of TFP bearing under near-fault earthquake ground motions with directivity focusing and fling step and compared with far-field ground motions. A set of 18 records comprising of six far-field and twelve near-fault ground motion, six with directivity effect and six with fling step, are used for the study. Behavior of TFP bearing is studied by changing the radius of curvature and coefficient of friction of outer surfaces contributing significantly under near-fault event. Further, a parametric study of TFP isolated building is also carried out using simple sinusoidal pulse motions to achieve clear insight of the effects of forward directivity and fling step. It is observed that near-fault ground motion with forward directivity pulses result in higher demands than the fling step pulses due to the backward and forward momentum gained during the initial and final phase of the directivity pulse. Moreover, TFP bearing is found effective in reducing base shear, absolute acceleration and isolator displacement compared to friction base-isolation system with single sliding surface.