Summary Seismic isolation is now being considered for nuclear power plant structures and has been applied to many nuclear structures including reactor buildings in France. A draft report entitled ‘Technical Considerations for Seismic Isolation Nuclear Facilities’ has been prepared by the USA Nuclear Regulatory Commission in 2010. It sets out to describe different types of isolators and recommends that lead plug isolators and FP isolators are acceptable choices for nuclear isolation systems. For the design of base isolation systems for nuclear structures, the design engineer is faced with very large design displacements for the isolators and supplementary dampers or highly damped isolators are prescribed to reduce them. These dampers reduce displacements but at the expense of significant increases in interstory drifts and floor accelerations in the superstructure. In this paper, an elementary analysis based on a simple model of an isolated structure is used to demonstrate this dilemma. The model is linear and is based on modal analysis, but includes the modal coupling terms caused by high levels of damping in the isolation system. Estimates of the floor response quantities are obtained by the response spectrum method. It is shown that as the damping in the isolation system increases, the contribution of the modal coupling terms becomes the dominant term. The results show that the use of damping in seismic isolation when the purpose of the isolators is to protect sensitive internal equipment is a misplaced effort, and alternative strategies to solve the problem are suggested. Copyright © 2014 John Wiley & Sons, Ltd.
Herein, novel graphene‐reinforced elastomeric isolators (GREI) are proposed. Elastomeric isolators (EIs) are special devices used for seismic isolation of structures. They are made of alternate layers of steel and rubber (steel‐reinforced EI [SREI]), and they position between the structure and its foundations to decouple them. The heavy weight and complex manufacturing process of SREI drives costs up, and this restricts their use to strategic buildings such as hospitals and civic centers. In recent years, alternative materials have been proposed to replace the steel sheets of SREI, e.g., glass or carbon fiber‐reinforced EIs (FREIs). However, their mechanical behavior requires further investigation before being implemented in existing and new structures safely. As a promising alternative, GREI is proposed here to overcome the heavy weight and long manufacturing process of SREI and the mechanical limitation of FREI to seismic excitations.
This paper is a theoretical and numerical study of the stability of light-weight low-cost elastomeric isolators for application to housing, schools and other public buildings in highly seismic areas of the developing world. The theoretical analysis covers the buckling of multilayer elastomeric isolation bearings where the reinforcing elements, normally thick and inflexible steel plates, are replaced by thin flexible reinforcement. The reinforcement in these bearings, in contrast to the steel in the conventional isolator (which is assumed to be rigid both in extension and flexure), is assumed to be completely without flexural rigidity. This is of course not completely accurate but allows the determination of a lower bound to the ultimate buckling load of the isolator. In addition, there are fewer reinforcing layers than in conventional isolators which makes them lighter but the most important aspect of these bearings is that they do not have end plates again reducing the weight but also they are not bonded to the upper and lower support surfaces. The intention of the research program of which this study is a part is to provide a low-cost light-weight isolation system for housing and public buildings in developing countries.
Herein, the mechanical behavior of a graphene‐recycled rubber compound is investigated by performing static and dynamic tests. Water‐based graphene suspension is deposited on recycled rubber pads via an electrostatic addition process. Results on tensile and compression tests indicate a significant improvement of the compound in strength and in damping. They also indicate that the compound experiences significant elongation (up to 500%) as well as withstands high tensile forces, 300% greater than the force that the recycled rubber mix would withstand. The effective compression modulus of the compound is also shown to increase by about 3.2 times at 10% strain with respect to the one for the recycled rubber mix. Results suggest that the graphene‐recycled rubber compound can deliver a sustainable solution for vibration mitigation applications.
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