Development Length of Straight FRP Composite Bars Embedded in Concrete

This article presents an analytical study performed on concrete girders reinforced with FRP bars with the goal of evaluating current design guidelines for FRP rebar development lengths. The analytical model is based on finite element formulation of embedded bar problems with inelastic constitutive laws for the constituent materials. The bond stress—slip behavior between FRP bars and concrete was calibrated from experimental data obtained from a large database set of 48 test specimens, most of which were collected from the open literature. The collected data was modified to emulate a specific bar size and embedment length for various scenarios. A large number of analytical simulations were conducted in order to investigate the effect of different parameters on the development length. These parameters include: bar type (GFRP, CFRP), bar strength, bar modulus of elasticity, bar diameter, bar surface coatings, concrete strength, and confinement. For each specimen, the analytical model was conducted for a set condition until an embedment length which satisfied a predetermined criterion was found. The analytical study resulted in the proposal of a refined design equation for development length of FRP bars for consideration by current building and bridge design codes.