Performance-based seismic retrofit of a bridge bent: Design and experimental validation

Abstract

Changes in the 2005 edition of the National building code of Canada resulted in an increase in earthquake hazard for some regions in Canada. This project studied the impact of this increase on a selected highway bridge. A seismic retrofit scheme, using carbon-fiber-reinforced polymers (CFRPs), was developed and applied to the selected highway bridge bent. The retrofitting technique is based on specific performance criteria under which the retrofitted structure must meet prescribed ductility levels corresponding to selected seismic events, and its design includes a new confinement model for reinforced-concrete columns wrapped with CFRP. Using this performance-based approach, the amount of required composite materials to achieve the specified criteria was found to be much more economical when compared with the ductility requirements in the 2000 edition of the Canadian highway bridge design code. The performance of the retrofitting technique was evaluated by pseudo-dynamic tests carried out on a 1:3 scale model of one of the bridge bents. Using the substructuring approach, the remainder of the structure was modeled, and the bridge bent was subjected to increasing levels of seismic loading, corresponding to various limit states of the bridge. The measured response of the test specimen compared well with the predictions of a three-dimensional (3D) nonlinear finite-element model calibrated with dynamic properties obtained from on-site ambient vibration tests. During the highest intensity test corresponding to a return period of 2500 years for a region of high seismicity, the CFRP retrofit showed no sign of distress, and the strain values measured on the fibers were very low, indicating that the performance-based design procedure is conservative.