Seismic FRP retrofit of circular single-column bents using a ductility wrap envelope to alter failure modes

The target displacement ductility requirements for circular reinforced concrete (R/C) single-column bridge bents are considered using a proposed multi-failure mode algorithm to determine the required thickness of fiber reinforced polymer wraps (FRPs). The procedure is developed using two in-house computer algorithms, PACCC (Plastic Analysis of Circular Concrete Columns) and PACCC-FRP, to generate a moment-curvature analysis using circular segments and subsequent failure mode predictions in single-column bents for both FRP-wrapped and unwrapped circular R/C sections. The results of the study were verified against published experimental tests at the ultimate force-deflection states of R/C sections and also against three commercial “software test beds”. The study uses PACCC-FRP to show that single-columns experiencing a brittle failure may be retrofitted with FRP wraps in order to increase the displacement ductility and satisfy target ductility values within the Ductility Wrap Envelope (DWE), or wrap-saturation level, as established herein.