Design of lead rubber bearings for bridges and their effects on bridge earthquake behaviour

A lead rubber bearing for seismic isolation of a three-span highway bridge with box girders was designed in this study. Also, the effects of lead rubber bearings and bridge column height on the bridge earthquake responses were investigated. For this purpose, a fixed based and an isolated bridge were analyzed using horizontal design response spectrum and the period, displacement and column internal forces were compared for different column heights. Additionally, the effects of characteristic strength and post-elastic stiffness, which determine the behavior of an elastomer bearing, on the bridge responses were investigated. An hand-made program was developed through the MATLAB programming language by utilizing the Open Application Programming Interface (OAPI) feature of the CSiBridge commercial bridge program in order to be able to conduct a large number of structural analyses parametrically. All the required analyzes were performed automatically and quickly with the help of this program. As a result of the conducted designs and structural analyses, the effects of the lower and upper bearing properties on the bridge responses in bearing design were observed. In addition, it was concluded that the lead rubber bearings significantly reduce the bridge responses compared to the fixed base and they are even more effective in bridges with short columns. Finally, the importance of careful selection of the bearing characteristic strength and post-elastic stiffness values in the bearing design was realized for decreasing the bridge responses.