Effective bond length of carbon-fiber-reinforced polymer strips bonded to fatigued steel bridge I-girders

After years in service, many steel girders have deteriorated to the point where fatigue cracks have initiated in the girders. In girders having cover plates that do not terminate in a compression region, a common type of crack initiates at the weld toe at the ends of the cover plate after being subjected to cyclic tensile loads due to traffic. The use of precured carbon-fiber-reinforced polymer (CFRP) laminates, adhered to the inside face of the girder tension flange, is one proposed method for repairing these cracked bridge girders. The main advantages of using CFRP laminates are their light weight and their durability, which result in ease of handling and maintenance. For the application of this rehabilitation method, it is important to determine the effective bond length for CFRP laminates adhered to the inside face of a cracked steel girder flange. Experimental tests using a new type of effective bond length test specimen were conducted in this research on several types of adhesives and precured CFRP laminates, in addition to several different bonding configurations. The minimum bond length required to achieve the maximum strength of the rehabilitation scheme for the materials investigated in this research was determined. The experimental results also indicated that an adhesive with relatively large ductility is required to redistribute the stresses successfully within the adhesive layer during increased loading. A simple analytical solution for the shear strain distribution in the adhesive layer was proposed for estimating the effective bond length, and the results were verified with computational analyses. Good agreement was found among the computational, analytical, and experimental results.