Dynamic Performance of Lead Rubber Bearings At Low Temperatures

Abstract eng:
Nowadays, even in areas that have not been well known for the application of seismic protective measures, there is a growing tendency to design highway bridges, especially curved ones, to withstand strong seismic demands. A commonly adopted earthquake protection strategy consists of using seismic isolation bearings instead of seismically vulnerable conventional bearings, to isolate the supported bridge deck from the ground movements below. Among the great variety of seismic isolation systems available, the lead rubber bearing (LRB), in particular, has found wide application in highway bridge structures. However, conventional LRBs, which are manufactured from standard natural rubber and lead, display a significant vulnerability to low temperatures. This paper describes the challenge faced in the seismic isolation using LRBs of a curved highway viaduct where low temperatures must be considered in the design. Specifically, the LRBs must be able to withstand temperatures as low as -30 °C for up to 72 hours, while displaying only minor variations in their effective stiffness. This extreme condition required the development of a new rubber mixture, and the optimization of the general design of the isolators. Since the relevant specifications such as AASHTO Guide Specifications for Seismic Isolation Design and EN 15129: Anti-Seismic Devices contain only limited test data relating to low-temperature performance, extensive full-scale low-temperature dynamic testing was carried out. This testing, which sheds new light on the performance of LRBs at low temperatures, will be described, in the context of the overall challenge to seismically isolate curved highway bridges.

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