PEER has just published Report No. 2014/08 titled “Unbonded Pretensioned Bridge Columns with Rocking Detail” as a new addition to the PEER Report Series. It was authored by Jeffrey A. Schaefer, Bryan Kennedy, Marc O. Eberhard, and John F. Stanton.
The columns and cap-beams of most bridges are built of cast-in-place reinforced concrete (CIP). The construction of CIP bridges often causes traffic congestion, and following an earthquake, they may be too damaged to function. To address these concerns, the authors have developed a new precast, pretensioned system. The precast feature reduces traffic delays by moving time-consuming construction activities off site. The pretensioning feature tends to reduce residual displacements after an earthquake. To minimize damage, deformations are concentrated at the columns ends, where a steel shoe confines the concrete. The use of epoxy-coated strands and the quality control available in a precasting plant will enhance durability.
The seismic performance of the system was evaluated with pseudo-static tests of two column-to-footing subassemblies. At the column base, one specimen incorporated ductile fiber-reinforced concrete (HyFRC) and a steel dowel bar that extended into the footing. The other column had neither any HYFRC nor a dowel. The first bar fracture occurred near a drift ratio of 6%, a value that can be controlled by varying the unbonded length of the reinforcement. Even after being subjected to drift ratios of over 10%, both columns had negligible damage to the concrete and residual drifts of only 0.5%.