Effet de la variation des paramètres caractéristiques des isolateurs sismiques affectés par la température sur le comportement des ponts isolés

Abstract

Seismic base-isolation design of bridges is established as a very effective alternative to the conventional design approach, based on the capacity design principle. Seismic isolation bearings are the main apparatus used to ensure adequate seismic behavior of base-isolated bridges. However, practically all seismic bearings are sensitive to many external and inherent effects especially low temperature effects. In fact, under cold temperatures, they typically show a more or less important increase of their characteristic strength and post-yield stiffness. Despite relatively known effects of low temperatures on base isolation systems characteristics, its impact on base-isolated bridges response and seismic demand in cold regions, especially within the recent Canadian seismic context, remain not enough studied and well understood by researchers and practicing engineers. This study aims the assessment of typical hysteresis features changes, especially those associated to low temperatures, on the seismic response and demand of isolated bridges located in eastern and western Canada seismic areas. Uniform-load method analyses were carried out in accordance with Canadian Highway Bridge Design Code (2006) and similarly developed according to the National Building Code of Canada (2010) in order to define seismic isolation reference system characteristics. Variations on these reference characteristics were introduced to simulate changes caused by cold temperature effects, other causes or within design optimisation. Afterwards, nonlinear time history analyses were performed on simplified “single degree of freedom” linear and nonlinear models and on tridimensional nonlinear ones. Results allowed to assess the seismic behavior of base-isolated bridges (in terms of maximum seismic force, maximum displacement and residual displacement) under changes in hysteretic features and low temperature. In a second step, the effect of pier flexibility was considered to study how it interacts with the previous parameters. Analyses results showed that changes in the hysteretic characteristics cause substantial changes on seismic demand of isolated bridges and that their effects differ significantly for eastern from western Canada. Cold temperatures, represented by an increase in stiffness and characteristic strength, induce increase in seismic force demand and a decrease in seismic displacement demand. Increasing pier flexibility resulted in a decrease of the seismic force demand. A similar effect was noticed for the seismic displacement demand however such effect became slightly insensitive to changes of the hysteretic characteristics of the isolation system for flexible piles. Temperature effects are found to be gradually more present for west coast forces whilst for east coast they remained important but decrease with the increasing of piers’ flexibility.

Date	10 Aug 2015
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Lotfi Guizani (Supervisor)