Use of bending test to determine the tensile strength and elastic modulus of GFRP bars

Fiber-reinforced polymer (FRP) composite bars have been increasingly employed to reinforce concrete members when the use of traditional steel bars would represent an issue for the durability of the structure. In fact, FRP bars have high strength-to-weight ratio, do not suffer of corrosion, and do not conduct electricity. Mechanical characterization of composite bars is complex due to the remarkable difference between bar properties in the direction parallel and orthogonal to the fiber. Therefore, direct tensile testing of FRP bars requires proper specimen preparation, which usually involves expensive bonding of metal pipes at the specimen ends. In this paper, a 3-point bending test is proposed as a possible alternative to the direct tensile test to obtain a quick and reliable estimate of the bar tensile strength and elastic modulus. An analytical model that accounts for bar shear deformation and large displacements is used to describe the specimen bending behavior. Forty bending tests of glass FRP (GFRP) bars with thermosetting or thermoplastic resin and four different diameters are presented and used to validate the test set-up and analytical model proposed. The results are compared with those of corresponding direct tensile tests showing the validity of the proposed bending test.