This study investigated retrofitting measures for improving the seismic performance of the substructures of existing bridges. Retrofit measures for both pile-supported and spread footings were investigated. Experimental tests were conducted on 1/3-scale footing and column assemblages which incorporated details that were selected to represent deficiencies present in older bridges. Retrofit measures were applied to both the columns and footings. The specimens were subjected to increasing levels of cycled inelastic lateral displacements under constant axial load. Specimen performance was evaluated on the basis of load capacity, displacement ductility, strength degradation and hysteretic behavior.
Tests on the as-built specimen resulted in a brittle failure due to insufficient joint shear strength in the column/footing connection. An added reinforced concrete overlay provided an effective retrofit for the as-built footings. The overlay resulted in increased shear resistance, allowed for the addition of a top mat of reinforcement to provide negative moment strength, and increased the positive moment capacity by increasing the effective depth of the pile cap. All retrofitted specimens developed plastic hinging in the columns with a resulting ductile response under the simulated seismic loading. Special detailing was required in the column lap splice regions in order to maintain the integrity of the splices. In specimens that were overturning critical, increased overturning resistance was provided by enlarging the footing plan size, by providing additional piles, or by providing tie-downs through the footing.