A shake table investigation on low-cost seismic isolation using unbonded scrap tyre pad isolators

Abstract

Seismic isolation is an effective strategy to mitigate the effect of earthquake on structures. Conventional seismic isolation is still inaccessible to developing countries as it is expensive. Scrap tyres have been identified to be suitable for use as base isolators. It is also a challenge to recycle, reuse and effectively dispose this rapidly accumulating waste material without harming the environment as it is heavy, thick and made up of multiple materials. In this paper, the effectiveness of using scrap tyre pads for base isolation is investigated. Scrap tyres of size 175/65/R14 are considered in the study. The tread portion of the scrap tyre is cut into pads of definite size and shape and arranged one above the other to form the isolator. The scrap tyre pads which contain both rubber and intervening steel cords make it vertically stiff and laterally flexible which will in turn reduce the cost of the system as they do not require additional materials for enhancing the stiffness properties. The application without steel end plates further reduces the cost and hence suitable as a low-cost seismic protection system for developing countries. In the present study square shaped unbonded scrap tyre pad isolators of three configurations using 4, 6 and 8 layers of scrap tyre pads are considered. Initially, the dynamic horizontal stiffness of different configurations of scrap tyre pad isolators is estimated using a shake table test on a system consisting of a set of rectangular plates supported by 4 isolators at the corners of the base plate. A shake table test is also conducted on a three storied scaled building frame model supported on four isolators at the four corners of the base of the model. All the isolators are found to be effective in shifting the fundamental time period of the frame. Finite element analysis on isolators with 4, 6, 8 and 10 layers are also carried out to determine the effect of vertical pressure on the fundamental frequency and dynamic stiffness of isolator systems.