Rubber bearings are widely used for seismic retrofit of bridges because they reduce the seismic force by making the vibration period of the bridge longer and distributing the seismic force to all the piers. However, they have the disadvantage of being easily aged compared to steel bearings as well as having variations in the shear stiffness. The shear characteristic changes in the blended rubber for the rubber bearings were analyzed, specifically, the aging accelerated by heat. The higher the aging temperature and longer the exposure time, the greater is the maximum stress and strain at that time, and the greater is the shear stiffness. This implies that the seismic performance gradually deteriorates due to aging as the service period becomes longer. This can provide the basis for the mechanical model of the aging bearing.
Generally, seismic performance objective of facilities is to minimize casualties by preventing collapse. Thanks to this performance the casualties in the past earthquakes were minimized in the advanced seismic engineering countries. However, they suffered from a great effort of recovering a social function because of heavy economical damage, which led a new seismic design paradigm to expand the current No-Collapse performance into Damage-controlled one. Because the seismic performance of our facilities is similar a severe damage will be led in earthquakes, which should be an obstacle in a rapid recovery of social system. The damage level should be restricted under a controlling level for a national earthquake-risk management and the performance of facilities should be assigned to meet this purpose. In this study the establishment scheme of seismic performance of facilities has been proposed to satisfy national seismic performance objective established in advance.
<p>Bridges with usual span lengths have been designed according to the Korea Bridge Code which allows large inelastic displacements. This code is, however, not applicable to cable-supported bridges. Recently new seismic design guidelines are being developed as one of the core tasks to develop super long-span cable-supported bridge technologies. New design earthquakes and seismic performance criteria are defined. The detailed performance requirements are assigned to each component of bridge. General cable-supported bridges have been designed seismically against an earthquake with a return period of 2400 years, but new guidelines adopt an earthquake with a return period of 4900 years as a design earthquake. The performance of a cable-stayed bridge designed in a conventional way has been investigated for the new design earthquake.</p>
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