Flexural Response of CFRP-Strengthened Steel Beams with Initial Bond Defects

This paper presents the flexural behavior of steel beams strengthened with partial-length adhesive-bonded carbon fiber-reinforced polymer (CFRP) plates under static four-point bending.An initial bond defect was intentionally introduced in the constant moment region of the CFRP-strengthened steel beams.In the experimental program, the test variables included the size of the initial bond defect, FRP modulus, FRP plate length, and condition of the steel beam before installation of the FRP plate (undamaged and preyielded conditions).Based on the test results, the presence of the initial bond defect changed the failure mode of FRP-strengthened steel beam from the fiber rupture to intermediate plate debonding.With the initial bond defect, the effectiveness of the FRP strengthening scheme decreased as FRP modulus increased.The stiffness, strength, and ductility index of the CFRP-strengthened beam with the initial bond defect decreased as the defect size increased.However, the initial bond defect had no detrimental effect on the maximum load capacity and ductility index of the strengthened beams.The strengthening effectiveness in terms of stiffness, strength, and ductility enhancement was more pronounced in the case of the pre-damaged steel beam, of which the bottom flange had already yielded before installation of the CFRP plate, than the undamaged steel beam.