Width factor for externally bonded FRP-to-concrete joints

The width factor is an important parameter that describes the properties of an externally bonded reinforcing plate-to-concrete bonded interface. The factor, which reflects the variation of bond strength due to change of the width of concrete substrate for a certain width of plate, is commonly derived from plate-concrete joint tests (also known as pull tests) indirectly. There, however, exists inherent and significant scatter in the test results that can adversely influence the empirically derived width factor. In order to investigate the reliability of width factor models, this paper reports the details of a three-dimensional (3D) finite element model (FEM) that considers debonding as concrete material failure by incorporation of a concrete damage-plasticity theory. A detailed analysis of the width factor is conducted using the FEM, from which a new model for the width factor of externally bonded (EB) fibre reinforced polymer (FRP)-to-concrete joint is proposed. The width factor is found to be a function of not only the FRP plate and concrete widths but also concrete strength and plate rigidity. It is found that most of the existing width factor models may overestimate the width effect.