Rolling-Ball Rubber-Layer system for the lightweight structures seismic protection: experimentation and numerical analyses

Protection of high-value building contents from seismic damage represents a worldwide challenging task. Artefacts, sophisticated medical and electrical equipment, high performance computer installations and other special contents have shown, in the last years, their high vulnerability both for high and moderate earthquakes. The lack of effective techniques, sufficiently developed for seismic risk mitigation of such objects, makes the seismic protection of contents a crucial issue. An effective means to provide this protection is seismic isolation. The isolation techniques to be used for the content are not a mere extension of the ones used for civil structures, although the basic theories and concepts of seismic isolation are the same. Indeed, the following technical peculiarities have to be considered: the contents have masses orders of magnitude smaller than those characteristic of civil structures and, secondly, they are often very vulnerable and are not able to withstand even small seismic actions. This thesis, that fits into this context, presents an innovative seismic isolation device for lightweight structures, named “RBRL” system, i.e. “Rolling-Ball Rubber-Layer”, and it is aimed at studying the dynamic behaviour of the system itself through numerical analyses and parametric experimentations, with the goals to get a sufficient comprehension of the system performance and its general numerical characterization. The device, invented by Alan Thomas at TARRC (“Tun Abdul Razach Research Centre”) comprises: a rolling-based bearing system, which allows any displacements in the horizontal plane; two rubber layers bonded to the steel tracks, which give an adequate damping to the rolling steel balls; some rubber springs, which ensure the recentering of the system through their elastic stiffness.