Effects of air temperature on the cyclic behavior of elastomeric seismic isolators

Abstract

Themechanical properties of elastomers can change significantly due to air temperature variations. In particular, prolonged exposure to subzero temperatures can result in rubber crystallization, with a considerable increase in the shear stiffness of the material. As a result, the seismic response of structures with elastomeric isolators can be strongly influenced by air temperature. Current seismic codes, indeed, require an upper and lower bound analysis, using suitable modification factors, to account for the changes in the cyclic behavior of elastomeric isolators due to air temperature variations. In this study, the sensitivity of the cyclic behavior of elastomeric isolators to air temperature variations is investigated based on the experimental results of an extensive test program on six different elastomeric compounds for seismic isolators, characterized by a shear modulus ranging from 0.5 to 1.2MPa at 100% shear strain and 20◦C. The cyclic tests have been performed on small-size specimens, subjected to shear strain amplitudes and frequency of loading typical for elastomeric seismic isolators, at seven different air temperatures, ranging from 40 to−20◦C. The effects of rubber\ud crystallization due to prolonged exposure to low-temperatures have been also investigated. A finite element model for the evaluation of the temperature contour map inside a full-size\ud elastomeric isolator exposed to low air temperatures has been also developed. In the paper, the experimental outcomes are compared with the modification factors provided by the current\ud seismic codes to account for the temperature effects on the mechanical properties of elastomeric isolators

An improved rheology model for the description of the rate-dependent cyclic behavior of high damping rubber bearings

“…These stress-softening behaviors seem to result from the healing of Mullins effect [20,21] occurring with the time lapse between finish of the preloading and start of the actual test. However, the temperature rise inside HDRBs is remarkable at low temperatures [8,36]. This rise also may cause some effect on stress responses in the 1st cycle of CS tests.…”

“…In order to minimize the self-heating effect [8,32] on the overstress parameter identification, the 1st cycle shear stressstrain response of sinusoidal loading tests are used in the parameter identification procedure. This assures achieving a thermal boundary condition compatible with the formulation.…”

“…1). In contrast to LRB, where rate dependence effect is much less significant even for low temperature cases [3,7], however, even after years of practice, some of the very important mechanical behaviors of HDR, such as the rate or temperature dependent behaviors are still difficult and less understood issues in engineering practice [8]. Yet, development of an advanced rheology model of HDRBs for designing base isolated structures in cold weather conditions and more general dynamic loading cases is much warranted.…”

Studying the standard's requirements for elastomeric seismic isolators by virtual testing

“…Some of scientific and technical sources [16,19,23] note dependence of horizontal stiffness and damping ratio on temperature and vibration frequency. The standard [4] also noted the behavior features of isolation bearings under vertical load such as creep and bedding.…”

Dynamic Response Changes of Seismic Isolated Building Due to Material Degradation of HDRB

“…Test results showed that low-temperature shear stiffness of the test bearings was almost twice as much as their room temperature stiffness. In two recently published papers [8,9], an experimental study to investigate the sensitivity of the cyclic behavior of elastomeric materials to air temperature variations on six different types of elastomers, characterized by a shear modulus ranging from 0.5 to 1.2 MPa at 100 % shear strain and 20 • C, are carried out. The cyclic tests have been performed at seven different air temperatures ranging from 40 to −20 • C. The effects of rubber crystallization due to prolonged exposure to low temperatures have been also investigated.…”