High-damping natural rubber (HDNR) bearings are extensively employed for seismic isolation of structures because of their low horizontal stiffness and high damping capacity. Filler is used in HDNR formulations to increase the dissipative capacity, and it induces also a stress softening behaviour, known as the Mullins effect. In this paper, a wide experimental campaign is carried out on a large number of virgin HDNR samples to better investigate some aspects of the stress softening behaviour, such as the direction dependence and recovery properties, and to characterize the stable and softening response under different strain histories. Test results are also used to define a model for simulating the response of HDNR bearings in shear that advances the state of the art in the description of the stress softening, which can be significant during the earthquake time history. The proposed model is used to analyse the seismic response of a simplified isolated structure modelled as an SDOF system under ground motions with different characteristics and by considering two different conditions for the bearings: one assuming the virgin (or fully recovered) rubber properties and the other assuming the stable (or fully scragged) rubber properties. The results show that, in the case of far-field records, the differences between the responses are limited although not negligible, whereas for near-fault records, modelling the bearings as being in their virgin state significantly reduces the effect of this kind of motion on isolated structures.

Stress softening behaviour of HDNR bearings: modelling and influence on the seismic response of isolated structures / Tubaldi, E.; Ragni, Laura; Dall'Asta, A.; Ahmadi, H.; Muhr, A.. - In: EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS. - ISSN 0098-8847. - STAMPA. - (2017). [10.1002/eqe.2897]

Stress softening behaviour of HDNR bearings: modelling and influence on the seismic response of isolated structures

RAGNI, LAURA
Membro del Collaboration Group
;
2017-01-01

Abstract

High-damping natural rubber (HDNR) bearings are extensively employed for seismic isolation of structures because of their low horizontal stiffness and high damping capacity. Filler is used in HDNR formulations to increase the dissipative capacity, and it induces also a stress softening behaviour, known as the Mullins effect. In this paper, a wide experimental campaign is carried out on a large number of virgin HDNR samples to better investigate some aspects of the stress softening behaviour, such as the direction dependence and recovery properties, and to characterize the stable and softening response under different strain histories. Test results are also used to define a model for simulating the response of HDNR bearings in shear that advances the state of the art in the description of the stress softening, which can be significant during the earthquake time history. The proposed model is used to analyse the seismic response of a simplified isolated structure modelled as an SDOF system under ground motions with different characteristics and by considering two different conditions for the bearings: one assuming the virgin (or fully recovered) rubber properties and the other assuming the stable (or fully scragged) rubber properties. The results show that, in the case of far-field records, the differences between the responses are limited although not negligible, whereas for near-fault records, modelling the bearings as being in their virgin state significantly reduces the effect of this kind of motion on isolated structures.
2017
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Descrizione: "This is the peer reviewed version of the following article: Tubaldi, E., Ragni, L., Dall'Asta, A., Ahmadi, H., and Muhr, A. (2017) Stress softening behaviour of HDNR bearings: modelling and influence on the seismic response of isolated structures. Earthquake Engng Struct. Dyn., 46: 2033– 2054. doi: 10.1002/eqe.2897, which has been published in final form at https://doi.org/10.1002/eqe.2897. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited."
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11566/247176
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