Bidirectional cyclic performance of reinforced concrete bridge column-superstructure subassemblies

The paper presents the methodology and findings from large-scale experiments conducted on reinforced concrete bridge subassemblies. Each subassembly consisted of the middle column/cap-beam joint of a three-column bridge bent and a large part of the monolithically cast-in-place box-girder of a typical California highway bridge. The subassemblies were subjected to constant gravity load and gradually increasing bidirectional cyclic lateral loading. One subassembly represented common practice in California and the other considered new design using headed reinforcing bars with reduced volume of transverse reinforcement to improve joint construction. When loading in the transverse direction, i.e., parallel to the cap-beam, the use of headed bars led to better global and local performances due to improved confinement of the joint region with less volume of reinforcement. On the other hand, when loading in the longitudinal direction, i.e., parallel to the box-girder, the headed bars were more engaged, as evident by their yielding, in confining the joint region than the conventional reinforcement. The effect of bidirectional loading on global damage of the box-girder slabs is presented as variation of the effective moment of inertia of the cap-beam cross section with displacement ductility indicating that Caltrans estimates are conservative up to displacement ductility of five.