000019725 001__ 19725
000019725 005__ 20170118182333.0
000019725 04107 $$aeng
000019725 046__ $$k2017-01-09
000019725 100__ $$aAhmadi, Hamid
000019725 24500 $$aAn Evaluation of Stress-Softening Behaviour of Hdnr Bearings on the Seismic Response of Base-Isolated Structures

000019725 24630 $$n16.$$pProceedings of the 16th World Conference on Earthquake Engineering
000019725 260__ $$b
000019725 506__ $$arestricted
000019725 520__ $$2eng$$aIn the last few decades, high damping natural rubber (HDNR) bearings have been extensively employed for seismic isolation of bridges and buildings because of their low horizontal stiffness and high damping capacity, which allows shifting the vibration period of the isolated structure away from where the earthquake input has the highest energy content and at the same time controlling the motion of the system. In HDNR material, filler is added to the natural rubber in order to improve its properties such as stiffness and dissipative capacity. The addition of the filler induces also a stress-softening behavior, known as “Mullins effect”. This effect makes the response of HDNR bearings path-history dependent and thus may influence the seismic performance of isolated systems. Published literature has suggested that the initial “virgin” properties of the material are eventually recovered. Accordingly, current seismic codes make the assumption that “Mullins effect” is a reversible phenomenon. The present work aims at studying the consequences of such strain-history dependent behavior on the seismic response of structural systems isolated with HDNR bearings. In particular, the first part of the paper reports a wide experimental campaign carried out on a large number of virgin rubber samples in order to better investigate some aspects of the stress-softening behavior of filled rubber, such as the direction-dependence and the recovery prosperities, and to characterize the stable and transient response under different strain histories. Test results are used to define a model for simulating the behavior of HDNR bearings in shear, which is an advancement in the description of both the stable and the transient behaviors. The proposed model has been used to analyze the seismic response of a simplified isolated structure modeled as a S-DOF (single degree of freedom) 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 obtained results show that, except for the special case of near-fault (NF) ground motions, the differences between the responses are limited although not negligible, whereas for NF records, the assumption of the virgin (or fully recovered) condition significantly reduces the effect of this type of motion on isolated structures.

000019725 540__ $$aText je chráněný podle autorského zákona č. 121/2000 Sb.
000019725 653__ $$aMullins effect, stress-softening, high damping rubber, seismic isolation

000019725 7112_ $$a16th World Conference on Earthquake Engineering$$cSantiago (CL)$$d2017-01-09 / 2017-01-13$$gWCEE16
000019725 720__ $$aAhmadi, Hamid$$iMuhr, Alan$$iRagni, Laura$$iDall'Asta, Andrea$$iTubaldi, Enrico
000019725 8560_ $$ffischerc@itam.cas.cz
000019725 8564_ $$s1145449$$uhttps://invenio.itam.cas.cz/record/19725/files/4256.pdf$$yOriginal version of the author's contribution as presented on USB, paper 4256.
000019725 962__ $$r16048
000019725 980__ $$aPAPER