Knock-off Effect of Steel Side Block as Displacement Restrainers on Dynamic Response of Isolated Bridge Structure

摘要

Displacement restrainers of the superstructure in the transverse direction of the isolated bridge are usually installed to protect expansion joints from damage during earthquake. Steel side blocks, one of the displacement restrainers, are set near both sides of isolating bearings. Here, a more rational seismic response of the isolated bridge in the transverse direction can be considered to be that the displacement of the superstructure during a small and moderate earthquake like Level 1 Earthquake defined in the JSHB (Specification of Highway Bridges) is restraint and the displacement during a strong earthquake like Level 2 Earthquake is released to mitigate damage of bridge pier and/or base structure and to enhance redundancy against a strong earthquake. For instance, steel side block, improved to have a knock-off function, will provide these responses of the isolated bridge. This study describes the outline of the side block with slit, which is developed by the authors to control the breaking load accurately. The breaking characteristics of the side block with knock-off function are verified through static breaking test using down-sized specimens with changes in dimension of the slit, like cross-sectional area and height of the slit. Also analytically clarified is the installation effect of the side block on dynamic response of the isolated bridge structures.