ANIDIS - L'ingegneria Sismica in Italia, ANIDIS XIX & ASSISi XVII - 2022

Dimensione del carattere:  Piccola  Media  Grande

Full-scale experimental tests on unbonded fiber reinforced elastomeric isolators under bidirectional excitation

Dario De Domenico, Paolo Longo, Daniele Losanno, Natale Maugeri, Giuseppe Ricciardi, Nicolò Vaiana

Ultima modifica: 2022-07-31


Fiber reinforced elastomeric isolators (FREIs) represent isolation devices that can be seen as an alternative to classical steel reinforced elastomeric isolators (SREIs). FREIs are manufactured by placing fiber reinforcement (either as fiber fabric or as dispersed short fibers) within the elastomer compound and eliminating the internal steel shims. Moreover, FREIs are usually installed without any anchorage system, i.e., according to a so-called unbonded configuration that exploits a simple frictional mechanism arising at the interface between the top/bottom face of the isolator and the structure. These isolators have been recognized in the literature as an emerging low-cost isolation strategy that can be particularly useful especially for developing countries. However, further research is needed on these devices, to investigate, especially at the full scale, the peculiar hysteretic characteristics and compare to those of classical SREIs.

In this contribution, full-scale experimental tests on two circular full-scale (diameter 620 mm) FREIs in unbonded configuration are presented. These tests, carried out at the EUROLAB of the University of Messina, Italy, involve both unidirectional tests (at various amplitudes, frequencies and under different axial loads) and bidirectional tests, i.e., application of imposed displacements along two orthogonal directions with simultanouesly applied vertical load. The wide range of experimental results offer a comphensive understanding of the hysteretic behavior of FREIs, encompassing both low-amplitude and high-amplitude motion scenario representative of weak and severe earthquake excitations, respectively. Furthermore, the comparison of main hysteretic parameters (typically, effective lateral stiffness and equivalent viscous damping ratio) obtained from unidirectional and bidirectional tests (at comparable amplitude levels) makes it possible to scrutinize the biaxial coupling effects of this type of isolators. To simulate such bidirectional interaction effects, a nonlinear phenomenological model, called multiple spring exponential model, is set up and calibrated based on experimental findings. Finally, the seismic response analysis of a three-dimensional reinforced concrete framed structure isolated with FREIs that are simulated through the proposed model is illustrated, accounting for and neglecting the lateral coupling of isolation devices.

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