Seismic Performance and Response of Seismically Isolated Curved Steel I-Girder Bridge

A 0.4-scale model of a three-span, seismically isolated, curved steel I-girder bridge was tested on multiple shake tables. The isolation system consisted of 12 lead-rubber isolators. The bridge is highly curved with total subtended angle equal to 104 degrees (1.8radians). The objectives of this study were: (1)investigate the effect of curvature on the seismic response of an isolated bridge, (2)evaluate the performance of reinforced concrete (R/C) columns during the design-level earthquake using seismic isolation, and (3)determine the failure limit states of an isolated bridge under extreme shaking. It was found that the horizontal curvature had little effect on the response of the isolators but it did cause asymmetry in the seismic response resulting in higher lateral displacements in the abutment isolators. Elastic performance was achieved in the R/C columns at the design earthquake level, with no concrete spalling in potential plastic hinge zones and only minor surface cracking. Essentially elastic behavior of these columns was observed even at earthquake levels equal to three times the design. Under large earthquake loads, the limit state was found to be excessive displacements in the isolators. Adequate vertical load capacity was maintained even at displacements exceeding the isolator diameter, when they are unstable by first-order theory. Isolator instability at an abutment and a pier did occur at three times the design earthquake, where the isolator shear strain was up to 400%. However, this instability did not cause bridge collapse because the isolators at other supports remained stable and the columns were elastic.