Evaluation of Vertical Stiffness of Scrap Tyre Pad Base Isolator with Change in Aspect Ratio

Earthquake has severe effect on all kinds of structures. Usually, seismic isolation is done in case of high-rise buildings. But from the past experiences it can be observed that the effect of earthquake is not only restricted to high rise framed structures, but also to the low rise unreinforced masonry structures. In developing nations, it is very expensive to finance earthquake isolation measures to safeguard buildings which are not classified as important buildings, such as houses or other minor structures, making the adoption of this type of system almost unfeasible. By incorporating low horizontal stiffness devices into the structure, it is possible to reduce the impact of seismic loads on those structures. The elastomeric bearings, sliding bearings and hybrid systems are the most commonly used type of base isolators. Due to the presence of synthetic or natural rubber and high strength reinforcing cords, the Scrap Tyre Pad (STPs) exhibits substantial vertical stiffness and horizontal flexibility. Hence it can be used as a suitable seismic isolation material for structures. In the present study, experimental evaluation of variation of vertical stiffness of STPs is conducted and an empirical modal relating the percentage increase in stiffness to percentage increase in aspect ratio is proposed.