Computational Technology Resources - CCP

Keywords: seismic isolation, high damping natural rubber bearings, scragging, property modification factors.

Summary

In 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 behaviour, 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 shown that the initial "virgin" properties of the material are recovered. Accordingly, current seismic codes make the assumption that "Mullins effect" is a reversible phenomenon. Thus, they suggest simplified methods based on the use of property modification factors for the bearing model properties to account for this effect in the seismic response evaluation of structures isolated with HDNR bearings.

The present paper is a study of the consequences of such strain-history dependent behaviour on the seismic response of structural systems isolated with HDNR bearings. In particular, the bearing behaviour is described by a non-linear process-dependent constitutive model based on one previously developed. This model allows separation of the contribution to the response due to the path-history dependent component from the contribution resulting from the stable (scragged) component. The model properties are calibrated against double-shear tests carried out on HDNR compounds commonly employed for seismic isolators. In particular, the response of a realistic isolated bridge is analyzed under ground motions with different characteristics 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 obtained for the two different conditions are compared to evaluate the influence of the Mullins effect on the bridge performance. This also permits an evaluation of the accuracy of simplified bearing models and relevant property modification factors suggested by the codes for the preliminary design and analysis of bridges isolated with HDNR bearings.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £75 +P&P)

	Computational & Technology Resources an online resource for computational, engineering & technology publications
	not logged in - login
Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 108 PROCEEDINGS OF THE FIFTEENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING Edited by: J. Kruis, Y. Tsompanakis and B.H.V. Topping Paper 158 Seismic Response Assessment of Base-Isolated Bridges accounting for the Stress-Softening Behaviour of High Damping Natural Rubber Bearings E. Tubaldi¹, H. Ahmadi², A. Muhr², L. Ragni³ and A. Dall'Asta¹ ¹School of Architecture and Design, University of Camerino, Italy ²Tun Abdul Razak Research Centre, Brickendonbury, United Kingdom ³Department of Civil Engineering, Construction and Architecture, Polytechnic University of Marche, Italy doi:10.4203/ccp.108.158 purchase the full-text of this paper Full Bibliographic Reference for this paper E. Tubaldi, H. Ahmadi, A. Muhr, L. Ragni, A. Dall'Asta, "Seismic Response Assessment of Base-Isolated Bridges accounting for the Stress-Softening Behaviour of High Damping Natural Rubber Bearings", in J. Kruis, Y. Tsompanakis, B.H.V. Topping, (Editors), "Proceedings of the Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 158, 2015. doi:10.4203/ccp.108.158 Keywords: seismic isolation, high damping natural rubber bearings, scragging, property modification factors. Summary In 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 behaviour, 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 shown that the initial "virgin" properties of the material are recovered. Accordingly, current seismic codes make the assumption that "Mullins effect" is a reversible phenomenon. Thus, they suggest simplified methods based on the use of property modification factors for the bearing model properties to account for this effect in the seismic response evaluation of structures isolated with HDNR bearings. The present paper is a study of the consequences of such strain-history dependent behaviour on the seismic response of structural systems isolated with HDNR bearings. In particular, the bearing behaviour is described by a non-linear process-dependent constitutive model based on one previously developed. This model allows separation of the contribution to the response due to the path-history dependent component from the contribution resulting from the stable (scragged) component. The model properties are calibrated against double-shear tests carried out on HDNR compounds commonly employed for seismic isolators. In particular, the response of a realistic isolated bridge is analyzed under ground motions with different characteristics 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 obtained for the two different conditions are compared to evaluate the influence of the Mullins effect on the bridge performance. This also permits an evaluation of the accuracy of simplified bearing models and relevant property modification factors suggested by the codes for the preliminary design and analysis of bridges isolated with HDNR bearings. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £75 +P&P)
Back to top	©Civil-Comp Limited 2023 - terms & conditions