ABSTRACT
The seismic and in-service performance of seismic isolation bearings is significantly affected by cold climates. The stiffness of rubber isolators and dry surface friction coefficient of curved surface sliding isolators increases considerably at extreme cold temperatures. An alternative design approach is presented in this paper where a special type of hysteretic damper with re-centering capability in combination with spherical sliding bearings with lubricated sliding surface are used together to minimize cold temperature effects. In this specific design arrangement, the dampers are attached to the deck using elongated holes (gaps), which are sized to accommodate the thermal displacements and hence to keep the dampers from being activated during thermal displacements. The gaps are sized based on the expected maximum thermal displacement in each pier. The gap length will thus be different for different piers. With this arrangement, the number of dampers engaged during an earthquake depends on the magnitude of the displacements. The distinct feature in this design is: (i) preventing the engagement of dampers under thermal displacements during service life without using shock transmitters and (ii) sequential engagement of dampers as a function of the magnitude of the seismically induced displacements. This paper presents a sample application of this methodology in the design of a major viaduct. The performance goals of the bridge require no damage at 475-year return period earthquake and repairable damage at 2475-year return period earthquake. The cold temperature test results of the isolation system, the design features of this seismically isolated bridge and the results of nonlinear time-history analyses are presented in this paper.
