ABSTRACT
In the recent past, passive isolation systems have been largely used as a valuable earthquake-resistant strategy in the design of civil engineering structures. In the future they are likely to become an established and reliable solution also for transportation network and infrastructures.
Failure of isolators is related to “beyond-design” conditions, i.e. extreme loading in case of very strong seismic events which lead to amplified multidirectional loading paths in the horizontal plane and to variable axial loading.
Reliable models of the behavior of seismic isolation devices, and the evaluation of their performance, has been successfully accomplished with selected constitutive material laws by FE modeling for moderate, to large, shear strain values.
The scope of this paper is to study the limit state and the beyond design response of filled isolator devices having different aspect ratios. Variable axial forces at increasing horizontal displacements have been thus considered in finite element analyses to highlight the dependencies of one on the other (Fig. 1). To this purpose three FE models of a circular HDRB have been developed within the MARC® FE code. The characteristics of the first HDRB device closely reproduce the prototypes designed and tested for the ELSY reactor within SILER project (Domaneschi et al. 2015). The other two are inspired by the geometry of bearing 601 and 302 in (Nagarajaiah & Ferrell 1999). Comparison of FE results: shear loading at different axial forces for device 302 at 400% and 250% shear strain. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig292_1.tif"/>
The devices models have been developed adopting the overlapping technique, which allows to predict the hysteretic behavior of rubber components by a suitable combination of simple constitutive models. The material modes have been tuned on results from tests and laboratory experiments.
The elastic-plastic component of the elastomeric layers has been successfully implemented for the reproduction of the device hysteresis at small value of shear deformations. However, this approach turned out to be not successful with shear deformations larger than 200%. Further research needs to be devoted to the implementation of special dissipative models, able to capture the physical behavior of the HDRB at larger values of shear strain.
The limit stress state condition of the device has been also assessed.
