Experimental Evaluation of Bridge Column Foundation Rocking Behavior

An experimental study was conducted at the University of Nevada, Reno, on the seismic performance of horizontally curved steel plate girder bridges. A two-fifth scale, three-span highly curved bridge was constructed on four shake tables and subjected to earthquake motions. Bridge footings were free to uplift during seismic loading, and neoprene pads were placed underneath the footings to simulate soil effects. Prior studies on the effect of rocking foundation systems concluded that rocking has the ability to reduce the damage in bridge columns in addition to being a good source of damping through the soil inelastic behavior. This paper describes the results from the experiment on a complete bridge system designed with rocking foundations. The rocking behavior was able to considerably limit the damage in the columns and the residual displacement of the bridge under earthquake motions equivalent to 2.5 times the earthquake intensity for which the bridge was designed. For high earthquake intensities, instead of experiencing overturning, the effect of rocking decreased, causing damage in the plastic hinge regions similar to a fixed-base column behavior. However, the overall damage was still less than in a fixed-base column.