Keywords: earthquake mitigation, seismic base isolation, elastic foundation, recycled tires, finite element analyses.

Seismic base isolation (typically using friction pendulum and lead rubber bearings) is an efficient building and bridge protection system against earthquake hazards that achieves seismic energy mitigation by decoupling the structure from its foundation. Numerous studies have been conducted on this topic over the last decades and many projects have successfully functioned with such systems. But on the other hand, the cost of the structure normally increases substantially. This study develops low-cost seismic base isolation of reinforced concrete buildings using scrap automobile tires to reduce the seismic distress on the superstructure. The use of scrap tires as rubber material in the so-called "elastic foundation" of buildings can provide an efficient way to reuse a large part of the huge stockpile of scrap tires all over the world (which is more than one billion used tires per year) and to attain significant environmental benefits by recycling useless scrap tires. Moreover, the low cost of the proposed seismic protection scheme is crucial for its application in developing countries that have inadequate financial resources and know-how for expensive earthquake mitigation techniques such as the typical seismic isolation devices. Another advantage of the proposed method is that it is not affected by the size of the project, while the more sophisticated practices available for use in construction and seismic retrofit are not economical for low to medium scale projects.

The idea for the use of tires for seismic hazard mitigation at the foundation of structures is a new one, and several recent studies of shake-table testing and numerical investigations on this topic can be found in the literature [1,2,3]. Reused tire rubber can be used alone in the form of tire pads (in a way similar to standard rubber bearings isolation), in sand-rubber mixtures (RSM) that replace large areas of the surrounding soil underneath the structure, or as in this study with special "cell cushions" made of old vehicle tires filled with sand and bundled with wire rope (to protect the structure from rocking motions) to approximate the sophisticated rubber bearing base isolators. An additional benefit gained when using this method is that it does not necessarily (i.e. when it is applied all over the foundation area) lead to large "rigid body" displacements of the superstructure, as in standard base isolation methods, which may be unacceptable in urban environments where very often buildings need to be constructed next to each other. The numerical results of this study illustrate that the response of the superstructure and the efficiency of the proposed elastic foundation method are sensitive to the characteristics of the structure and the low-cost isolation, and mostly on the frequency content of the excitation.

1

A.W. Charleson, M.A. French, "Used car tire straps as seismic reinforcement for adobe houses", in Proc. 14th WCEE World Conference on Earthquake Engineering, October 12-17, Beijing, China, 2008.

2

H.-H. Tsang, "Seismic Isolation by Rubber-Soil Mixtures for Developing Countries", Earthquake Engineering and Structural Dynamics, 37, 283-303, 2008. doi:10.1002/eqe.756

3

A. Turer, B. Ozden, "Seismic base isolation using low-cost scrap tire pads (STP)", Materials and Structures, 41, 891-908, 2008. doi:10.1617/s11527-007-9292-3

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