Enhancing Seismic Performance of Bridge Cap Beam-to-Column Joints Using Prestressing

Conventional seismic design of bridge cap heamto-column joints adapted from building design methods based directly on maximum shear forces can result in non-constructable reinforcement details. In an effort to establish an alternative design procedure, three bridge tee joint systems with circular columns were designed and tested under simulated seismic loading. The design of the tee joints was based on a rational approach treating joint shear as a component of the complete joint force transfer mechanism. This enabled the amount of reinforcement to be minimized within each test joint. In two of the three tee joints, cap beam prestressing was used to reduce the joint reinforcement further when compared to an equivalent joint with zero prestressing. The feasibility of precast fabrication of concrete bridge joint systems consisting of fully prestressed cap beams was also demonstrated in one of the tests. Test results indicate the superiority of performance of bridge joints incorporating prestressing, despite the reduced amount of reinforcement.