The characteristics of the seismic bearing change depending on various factors. When an earthquake occurs, the behavior of the bridge may differ from the values expected in the structural design. The shear deformation of the seismic bearing may increase, but it is difficult to reach the fracturede formation. This paper studied the effect of the stiffness due to various dependency and durability on Lead Rubber Bearings (LRB) and the over strength of bridge piers on the bearing behavior when an earthquake occurred. As a result, if the stiffness of LRB reduces within the criteria, seismic performance can be expected safety even if the shear strain designed in the current design is greater than the allowable shear strain. The reason is that the hardening phenomenon in the high strain region of the laminated rubber bearing suppresses the displacement. Also, since the seismic bridges with over strength of the piers have come near elastic behavior when an earthquake occurs, shear strain is easy to be large.
Recently, some weaknesses of a lead rubber bearing (LRB) have been identified such as excessive tensile stress at some basemat-edge isolators and degradation of lead plug damping performance by temperature rising due to responses during the large and long duration earthquakes. The degradation of lead plug damping performance has become a design factor and a concern with response evaluation method to consider the thermal effect to lead plug has been growing. In this paper, to study the degradation of lead plug damping performance, firstly loading tests (a multi-cyclic loading tests to get thermal conditions of the lead plug, and a horizontal/vertical directional loading tests to get mechanical behaviors of the LRB under multiple degree of freedom loading) for LRB specimens were performed, then an analysis program to simulate the tests are newly developed that are validated by comparing to the test results. By these tests and analyses, some new findings are given on heat generation characteristics of the lead plug along with its thermal boundary conditions. By checking the LRB performance after the loading tests, another finding is given that mechanical characteristics are almost recovered when the lead plug temperature is enough cooled even that was once heated up to 300 degrees Celsius.
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