Effective surface deformation height and bond rigidity of GFRP reinforcing bars with ribs

This study focuses on the evaluation of the surface deformation height of ribbed type of GFRP rebars. The bond behaviour of ribbed type of GFRP rebar is investigated in terms of the effective deformation height and bond rigidity, both experimentally and numerically. Pullout tests on ribbed type GFRP rebars embedded in concrete have been conducted to obtain an accurate bond stress-slip law and also to closely observe the state of the surface of pulled-out rebars at failure, in order to categorise accurately the mode of failure. In the pullout tests, the high temperature regime is particularly considered. In addition, finite element (FE) simulations of the specimens subjected to pullout tests are developed. From the FE analyses and the experiments, the effective surface deformation height and bond rigidity of the GFRP rebar with ribs was determined. The numerical results were substantiated by the experimental findings and good agreement was observed. Moreover, adding milled glass fibres in the surface deformations could not increase the effective surface deformation height and bond rigidity of the rebar; however, it seems to improve the bond strength because increasing the proportion of milled glass fibres improves the connections between the core and rib section.