Seismic Protection of Buildings by Rubber-Soil Mixture as Foundation Isolation

Introduction

For the past several decades an important issue for structural and geotechnical engineers is to find a way to reduce structural response caused by earthquake effects. Many concepts have been evolved regarding this purpose. There are numbers of the mechanism by which the dynamic control action is achieved. To find an economical and feasible way to protect structures from damages due to the earthquake is still an important aspect of civil engineering. One of the approaches used for this objective is seismic isolation system. A seismic isolation system is defined as a flexible or sliding interface positioned between a structure and its foundation for the purpose of decoupling the horizontal motions of the structure, thereby reducing earthquake damage to the structure and its contents. In the conventional approach, this objective is reached by designing a structure with adequate strength and ability to deform in a ductile manner. In this regards the necessary flexibility can be achieved by the use of rubber base isolation technique. Rubber bearing offers the simplest method of base isolation and they are being used for past three decades (Kelly, 1996). There are so many other base isolation systems which are already explored and reviewed by various researchers (Jangid & Datta, 1995, Patil & Reddy, 2012, Datta, 2003). But all those conventional systems are not feasible and economic for developing countries like India. United Nations Industrial Development Organization (UNIDO) active in developing low-cost seismic isolation system. The concept of low-cost and effective earthquake protection techniques using natural material like sand was looked at by Qamaruddin and Ahmad (2007), Feng et al. (1993), Nanda et al. (2012), etc.

Soil reinforced with natural rubber demonstrates an increase in energy dissipation capability (Edil & Bosscher, 1994) and can act as a low-cost base isolator. The feasibility of using shredded rubber mixed with sand as a natural base isolator was investigated analytically by Tsang (2008). Neoprene rubber cushions separate the violent shock waves in the ground from the building foundations and used tires have been proven to be a good shock absorber (Edeskä, 2010). Laminated rubber bearing is currently the most commonly adopted system due to the strength required in the vertical direction to support the full weight of the building. At present, owing to the tremendous cost of implementing base isolation technique, applications can only be seen in structures with critical or expensive contents.

There is an increasing interest in developing countries to apply low-cost seismic isolation to public buildings like office buildings, schools, hospitals etc. The significance is that the cost of isolation system used should be economic compared to the cost of replacement due to earthquake damages. In this paper presents results of numerical simulation of a 3D building model resting on a layer of sand and sand mixed with shredded rubber mixture as a low-cost isolation system in ABAQUS environment. The effectiveness of the aforesaid isolation scheme is studied numerically, as well as parametric studies are also done.