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Thermal degradation of the performance of elastomeric bearings for seismic isolation


Concern about reliability of elastomeric bearings is increasing along with the rapid development in application of such devices. Studies on experimental and in-service bearings have revealed the occurrence of permanent and transient changes in engineering properties of these devices. This property loss, however, varies in quality and magnitude, depending on service or environmental conditions at which bearings are employed. Knowledge about the magnitude of the lost property and the rate of degradation is critical for the safe performance of the isolated structure. Availability of such measures helps avoid unnecessary cost and service interruptions of bridge structures by optimizing monitoring and maintenance activities. It is necessary to identify the service and environmental conditions contributing in such degradation phenomenon. A literature review does not indicate the availability of complete and comprehensive studies on this topic. The focus of this research study is to identify and quantify property loss of elastomeric bearings, particularly due to heat, when they are subjected to cyclic lateral load under different environmental conditions. This research also proposes a methodology for a precise and accurate prediction of the temperature profile within the body of an elastomeric bearing. This methodology can be incorporated with the existing numerical models to assess the adequacy of performance of such bearings through seismic events. The reversible changes in characteristics of lead plugs, which take place mainly due to heat, were found to represent the main sources of transient changes in characteristics of an elastomeric bearing. Elastomeric bearings are also subjected to irreversible degradations such as stiffening of bearings as a result of hardening of rubber as when they are exposed to high temperature. High temperature is the result of generation of heat through hysteresis action of lead plugs

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