Pre-stress bonded composite patch is a promising technique to reinforce steel member damaged by fatigue. ifhe effectiveness of this technique was verified by fatigue tests on notched steel plâtes. Results showed that the application of carbon fibre reinforced plastic (CFRP) strips and, eventually, the introduction of a compressive stress by pretension of the CFRP strips prior to bonding produced a significant increment of the remaining fatigue life. In this paper, the stress intensiqr factor in the notched plates is computed by a two-dimensional finite element model in connection with the three-layer technique in order to reduce the computational effort. Due to high stress concentrâflon at the plate crack tip, debond is assumed at the adhesive-plate interface. The goal is to illustrate the influence of some reinforcement parâmeters such as the composite strip stiffness, the pre-stress level, the adhesive layer thickness and the size of the debonded region on the effectiveness of the composite patch reinforcement.Keyvords composite patch; fatigue crack reinforcement; parametric analysis.In Bassetti5 a novel technique was proposed to reinforce steel member damaged by fatigue. It consists in the appiication of carbon fibre reinforced plastic (CFRP) strips and, eventually, the introduction of a compressive stress by pretension of CFRP strips prior to bonding. Note that this new methodology applied to riveted steel members avoids the drawbacks of standard reinforcement techniques such as hole drilled at crack fiont, cover plates application, replacement of rivets by high strength bolts, cold expansion of the rivet hole and welding of the detected cracks. effectiveness of pre-stress CFRP-strips to stop fatigue crack emanating from the rivet hole or to prevent further cracking at other locations. The carbon fibre reinforced plastic laminates have physical and mechanical properties particularly interesting for reinforcement of fatigue damaged steel elements. The high fatigue resistance of CFRP avoids crack propâ-gation from the cracked steel section into the patch. The high stiffness of CFRP reduces the stress range in the cracked steel section and promotes crack bridging. llhe high tensile strength of CFRP allows also the application of a pretension to composite strips in order to increase the effectiveness of the bonded patch on thicker steel section. Finally, the low self-weight of CFRP plates limits the dead load increment and simplifies the strengthening operations. Composite patch reinforcement technique is a standard and reliable procedure in different engineering branches to reinforce structural elements subjected to extreme actions (high fatigue loads, high temperature ranges and exposure to aggressive agents) and nowadays, is also a standard reinforcement methodology in aircraft industries.T In fact the CFRP laminates is becoming a familiar procedure for O 2003 B ackwe I Publ sh ng Ltd. Fatigue Fract Engng Mater Struct 26, 59-66

a b s t r a c tFor the repair of damaged steel beams, Carbon Fibre Reinforced Polymers (CFRP) are effective under monotonic loads, but less information is available under fatigue loading. In this paper, fatigue tests were performed on nine CFRP reinforced cracked steel beams. The fatigue crack propagation curves showed that CFRP strips reduce the fatigue crack growth and extend the fatigue life. Experimental results also revealed the presence of a debonded area between the reinforcement and the steel substrate at the crack location. Debonding clearly has a detrimental effect on the reinforcement effectiveness. Finally, numerical and analytical studies are performed and compared to the experimental findings.

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