Strut-and-Tie Analysis of Bridge Tee Joints Subjected to Seismic Actions

The seismic design of cap beam-to-column bridge joints improved dramatically after the 1989 Loma Prieta earthquake, during which many bridge joints were significantly damaged. Because of high shear force resulting in congested joint reinforcement, researchers began investigating alternative design methods for bridge joints that would produce constructible details. A methodology based on a force transfer model received considerable attention and is now widely used in the United States. This model uses vertical stirrups placed outside of the joint panel to transfer forces across the joint. Using several large-scale bridge joints with varying amounts of cap beam prestressing, this design methodology was investigated under simulated in-plane seismic loading. Although good seismic performance was observed for joints with cap beam prestressing, joints without prestressing in the cap beam failed at moderate to large displacement ductilities. Supported by experimental data, strut-and-tie analysis was performed on three bridge tee joints. The analysis identified shortcomings of the design force transfer model and revealed that the design model could be simplified with subsequent reduction to the reinforcement in the joint region when applied to prestressed joints.