Calabrese, Andrea Analytical, Numerical and Experimental Study of a Novel Low-Cost Base Isolation System. [Tesi di dottorato]

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Abstract

The earthquakes of L’Aquila (2009) and Haiti (2010) showed, once again, the dramatic consequences of seismic events striking brittle, heavy and poorly constructed buildings. Worldwide, the high number of earthquake casualties still motivates structural engineers to search for effective seismic prevention technologies that can be adopted on a large scale. This work is oriented to introduce an innovative base isolation system: Recycled Rubber-Fiber Reinforced Bearings (RR-FRBs). These devices consist of several layers of recycled rubber, and are reinforced with sheets of composite materials. Compared to traditional rubber isolators, the weight and the cost are reduced by using fiber-reinforcements, no end-plates, and no bonding to support surfaces. The use of a flexible reinforcement, together with the absence of any constraint to the support surfaces, eliminates the presence of tensile stresses in the bearing under shear actions. This allows using a low quality rubber, as the one obtained from exhausted tyres or industrial leftovers. These materials are available everywhere in large quantities, they are inexpensive, and can be easily transformed with simple industrial processes. Consequently, RR-FRBs are a very low-cost technology. With the scope of assessing the use of RR-FRBs for seismic protection of buildings, this dissertation presents a comprehensive theoretical and experimental study. Firstly, closed-form expressions describing the compression and shear behavior of RR-FRBs are analytically obtained based on linear-elastic theory. These solutions are meant to be applied as design formulas for the devices. Finite Element Analyses (FEAs) are then performed, and the results are used as benchmark for the analytical expressions. A third phase of the research is dedicated to the experimental characterization of the recycled rubber. Based on derived material properties, analytical and FEAs results, prototypes of RR-FRBs are designed, manufactured and tested. The acquired knowledge of the behavior of the bearings is used to analyze a case study. Inelastic time-history analyses are performed on a prototype representing a common residential building typology. Numerical results show the high potential of such low-cost isolators in reducing the seismic damage to housing structures. It is hoped that the outcomes of this research could contribute to mitigate human life losses in developing countries located in earthquake-prone regions of the world.

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