The mechanics of fiber reinforced multi-layered elastomeric isolation bearings is studied in this paper. Such bearings offer the possibility of light-weight low-cost seismic isolators that can be mass-produced and used for public buildings and housing of highly seismic areas in developing countries.
The fiber reinforcement, in contrast to the steel reinforcement in conventional isolators, assumed to be rigid both in extension and flexure, is flexible in extension, but completely without flexural rigidity. In addition the rubber layers in these bearings tend to be very thin leading to large shape factors and the need to include bulk compressibility in the elastomer. These aspects of the bearings lead to interesting mechanics problems and in this paper the influence of the stretching of the reinforcement and the compressibility of the elastomer on the mechanical response is developed and confirmed by finite element analyses. A surprising result of the analysis of the combined response of the apparently unrelated effects of stretching of the reinforcement and compressibility in the elastomer is that the mathematical structure of the theory is the same for both effects and that they can be combined in the result- ing solution in a simple way. It is shown that it is possible to produce a fiber-reinforced isolator that matches the behavior of a steel-reinforced isolator. The fiber-reinforced isolator will be significantly lighter and could lead to a much less labor intensive manufacturing process.
Base isolation
Base Isolated Building with Hybrid Base Isolation System (HDRB & FS in parallel): Linear vs. Nonlinear Dynamic Analysis
In this work, the base isolation system for a multi-storey reinforced concrete building, highly irregular in plan, has been considered. The hybrid base isolation system consists in High Damping Rubber Bearings (HDRB) in parallel with Friction Sliders (FS) with low coefficient of friction at the interface steel-PTFE. In particular the HDN.E 500 and AlgaPot PNm devices are adopted. The seismic analysis has been performed with all possible linear and nonlinear dynamic analysis according to Eu- ropean seismic code (EC8) and according to the new Italian seismic code (NTC 2008). The results of the seismic analysis have been compared closely, in terms of stresses on the main elements of the superstructure (bending mo- ment and shear force for the beams; biaxial bending moment, the axial and shear force for columns) and in terms of deformation of the superstructure (interstorey drift). In this work, has been evaluated the influence of the accidental eccentricity in the non linear dynamic analysis in order to account for uncertainties in the location of masses and in the spatial variation of the seismic motion. Con- sidering the accidental eccentricity in a nonlinear dynamic analysis, the number of tests to be performed increases substantially, so it is important to understand how the accidental eccentricity influences the seismic response of base-isolated structure.
For this paper is available an extended abstract after the text in Italian
New passive control strategy for seismic upgrade of essential buildings: base isolation and tuned mass damping
A new passive control strategy, which combines base isolation and tuned mass damping to retrofit essential buildings, is herein discussed. In particular, the hypothesis of application of this strategy on Villa d’Agri’s Hospital (PZ) is presented. The effectiveness of the proposed approach has been evaluated in comparing linear and non linear seismic response of the isolated system, with and without TMD, to recorded accelerograms. The BI&TMD combined control strategy reduces displacements at the base without affecting the beneficial effects of isolation on the superstructure seismic response. Numerical results show higher control strategy effectiveness in the case of seismic excitations with high energy content in a low frequency range.
Available in Italian only