Comparison of the Seismic Retrofit of a Three-Column Bridge Bent with Buckling Restrained Braces and Self Centering Braces

A three-column bridge bent of an actual bridge constructed in 1963 in Salt Lake City was evaluated for seismic load capacity and displacement ductility. The bridge was constructed before the 1971 San Fernando earthquake, and as such was missing the reinforcement details necessary to provide adequate load capacity and displacement ductility. Two seismic retrofit schemes, the first using buckling restrained braces (BRB) and the other using self centering braces (SCB), are examined in this paper. The BRB inelastic behavior is represented using the Menegotto-Pinto model to reproduce isotropic and kinematic strain hardening properties. Flag-shaped hysteresis with slip deformation and bearing is used to represent the SCB. Nonlinear time-history analyses were performed to assess and compare the seismic performance of the bridge bent in the transverse direction for the as-built and retrofitted three-column bridge bent. The bridge bent was evaluated under several performance limit states using far-field records from FEMA P695, which were scaled to the maximum considered earthquake level at the site. The results show that retrofit with either BRB or SCB components improves the seismic performance of the bridge bent under serviceability and ultimate limit states by decreasing drift demands, as well as maximum steel and concrete strains in the reinforced concrete columns. SCBs and BRBs reduce damage to concrete columns by dissipating energy. BRBs perform better than SCBs in reducing the peak drift of the bridge bent. However, retrofit with SCBs reduces the residual drift of the bridge bent for earthquake records with high peak ground accelerations to acceptable levels. SCBs are less effective regarding energy dissipation due to the flag shaped hysteresis but they keep residual drifts small, thus increasing resilience and keeping repair costs low.