Upgrading steel–concrete composite girders and repair of damaged steel beams using bonded CFRP laminates

This study investigates the strengthening of intact steel–concrete composite girders and the repair of notched steel beams, using carbon-fibre-reinforced polymer (CFRP) materials with Youngʹs modulus varying from 150 to 400 GPa. Three large-scale (6100 mm long) steel–concrete girders scaled down (4:1) with accurate proportional dimensions from a bridge, were tested. Also, 15 small-scale (1000 mm long) W-sections with various levels and configurations of loss in the tension flange, induced by notching, were tested. Flexural strength and stiffness of the composite girders were increased by 51% and 19%, respectively. The outer CFRP short layer debonded prematurely, followed by concrete crushing. No debonding occurred between the inner CFRP layer and steel. Complete cutting of tension flanges in W-sections reduced their ultimate capacity and stiffness by 62% and 45%, respectively, whereas 50% loss of the flanges resulted in insignificant reductions. In the former, the CFRP repair resulted in strength recoveries, up to 79%. In the latter, insignificant gains were observed. A model was developed for CFRP-strengthened composite girders, verified, and used in a parametric study. It showed that the higher the CFRP modulus, the higher the gain in stiffness, but the lower the gain in flexural strength, due to the inherent reduction of tensile strength of CFRPs with higher modulus.