Effect of near and far field earthquakes on performance of various base isolation systems

Abstract

Civil engineering infrastructures are prone to natural disasters like earthquakes, floods and strong winds. Base isolation is one of the effective structural controlling technique for protection of structure during earthquake events. The concept of Base isolation is to insert a flexible layer between foundation and superstructure thus decoupling the building from damaging action of ground motion. This modifies the dynamic characteristics of the system. This paper presents comparative study of near and far field earthquakes on the performance of three types of passive base isolators namely High Damping Rubber bearing (HDRB, Damping Ratio: 13%), Low Damping Rubber Bearing (LDRB; Damping Ratio: 3%) and Lead Core Rubber Bearing (LCRB, Damping Ratio: 25%). For this purpose, an 8-storey structure has been analyzed using state space approach in MATLAB. Parameters like peak global drift, inter-storey drift, transmissibility of acceleration are compared for various base isolation systems under near and far field earthquakes. It is concluded that the dynamic response of the structure depends on the source of excitation and designer must consider this effect for efficient design. Moreover, the damping of the base isolator should be so adjusted that both the deformation and transmissibility ratio are minimized or in some cases a combination of different dampers may be used.