Evaluation of the capacity of a bridge to carry self-weight and traffic loads after an earthquake is essential for a safe and timely re-opening of the bridge. In California, modern highway bridges designed using the Caltrans Seismic Design Criteria are expected to maintain at minimum a gravity load carrying capacity during both frequent and extreme seismic events. However, no validated, quantitative guidelines for estimating the remaining load carrying capacity of such bridges after an earthquake event exist today.
In this study, experimental and analytical methods were combined to evaluate the post- earthquake traffic load carrying capacity of a modern California highway overpass bridge. An experimental study on models of circular reinforced concrete bridge columns was performed to investigate the relationship between earthquake-induced damage in bridge columns and the capacity of the columns to carry axial load in a damaged condition. The test results were then used to calibrate a finite element model of a bridge column. This bridge column model was incorporated into a hybrid model of a typical California overpass bridge and tested using the hybrid simulation technique. The finite element model of the typical California overpass bridge was validated using the data from hybrid simulations. The validated model of the typical bridge was used to evaluate its post-earthquake truck load capacity in an extensive parametric study that examined the effects of different ground motions and bridge modeling parameters such as the boundary conditions imposed by the bridge abutments, the location of the truck on the bridge, and the amount of bridge column residual drift.
The principal outcomes of this study are the following findings. A typical modern California highway bridge is safe for traffic use after an earthquake if no columns failed and the abutments are still capable of restraining torsion of the bridge deck about the longitudinal axis. If any of the columns failed, i.e., if broken column reinforcing bars are discovered in an inspection, the bridge should be closed for regular traffic. Emergency traffic with weight, lane, and speed restrictions may be allowed on a bridge whose columns failed if the abutments can restrain torsion of the bridge deck. These findings pertain to the bridge configuration investigated in this study. Additional research on the post-earthquake traffic load capacity of different bridge configurations is strongly recommended.
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