Iterative determination of threshold FRP area needed to avoid non-ductile longitudinal shear failures in yield-zones of FRPRC members

This paper presents a novel nonlinear iterative scheme to determine threshold areas of FRP plating which avoid longitudinal shear failure of the FRP-to-concrete connection in yield zones of FRPRC beams. Implicit differentiation of an experimentally-verified predictive model for longitudinal shear failure and of associated FRPRC section equations is used to generate incremental expressions which underpin the iterative scheme. Iterations are driven by the disparity between the longitudinal shear stress for the updated area of plate and the connection’s longitudinal shear strength. For different load types on a FRPRC beam, the scheme is shown to exhibit robust convergence characteristics in regimes of pronounced nonlinearity, with reliable gravitation toward the correct plate area from a wide range of starting values of this plate area. The study produces the counter-intuitive result that stiffer plates reduce longitudinal shear requirements, probably owing to the associated shorter yield zones of reduced yield activity at the specified peak load of the FRPRC member.