Seismic retrofit of curved bridges on soft soils using buckling restrained braces

Damage to bridges has been evident during many earthquakes, even when the structure was designed according to model codes. Abutments act like a retaining wall during a seismic event. Past studies show that there have been several incidents of damage to abutments and shear keys due to pounding. This research attempts to study the performance of an existing multispan curved bridge supported on rigidly capped vertical pile groups which pass through a deep layer of soft clay. The soil-structure interaction (SSI) between the pile group and soil is idealized as linear springs in two perpendicular horizontal directions. At the expansion joints and abutments, steel shear walls are provided to improve the performance and concrete shear keys are utilized to restrain the lateral movement of the girders and deck during seismic events. A seismic retrofit scheme using Buckling Restrained Braces (BRB) is implemented at the abutments to prevent pounding damage. It is observed that the soft soil surrounding the piles has a significant effect on the dynamic response of the bridge; in addition, the bearing displacements are underestimated if SSI is ignored. Damage to the abutments and the deck due to pounding can be prevented by using a combination of BRBs. Similarly, pounding between steel girders at the expansion joints can be prevented by using BRBs instead of seismic restrainer rods. BRBs are idealized using bilinear plastic link elements with a backbone curve adopted from actual experiments. A sensitivity analysis is carried out for modeling the BRBs using two different software packages.