Evaluation of bond in the deformability indices of CFRP pretensioned concrete structures

Failure modes by concrete crushing and increased deformability are considered key design considerations in CFRP prestressed concrete beams, to enhance the warning message before collapse. However, upon unloading considerable elastic energy can be released in concrete when FRP tendons are adopted that can lead to horizontal cracking and sudden failure. There seems to be limited understanding in the effect of bond in the crack formation and propagation and the resulting energy dissipation mechanisms in CFRP pretensioned structures. The aim of this study is to investigate the progressive failure and energy dissipation of CFRP pretensioned concrete beams via progressive bond degradation, crack formation and inelastic concrete softening and evaluate deformability indices as found in literature and design guidelines. A CFRP pretensioned concrete beam with distinct bond differences (high and low bond) is studied in four-point bending and after cyclic loading (load-unload) using the finite element software ABAQUS. High bond tendons result in extensive cracking compared with low bond tendons but the effect of pretesioning force greatly affects the slope of the unloading curve and the resulting elastic energy observed in the load-displacement plots among different bond scenarios. Current deformability indices need to be revised to account for the effect of prestressing in CFRP prestressed concrete beams.