Mechanical Anchorage to Enhance the Bond Strength of Prestressed CFRP Laminates Bonded to Structural Steel Beams

Abstract

The carbon fibers (CFRP) in the form of laminates can be applied to retrofit flexural concrete and steel members. However, interfacial stress between the CFRP and steel surface tend to be high especially at the edges of the laminates. Strengthening systems with prestressing is suggested in order to effectively utilize the CFRP to overcome the failure mode caused by debonding. Applying prestressing force to CFRP laminates bonded to steel or reinforced concrete beams can be done by using mechanical anchorage. Adding mechanical anchorages to the ends of the laminate can ensure a better ductile behaviour and can also increase the allowable level of prestressing. In the present research, a mechanical anchorage prestressing system is introduced in order to maintain the initial prestressing applied to the CFRP laminates, and delay the premature debonding failure. A numerical analysis and an experimental program was conducted on steel I-beam sections subjected to flexure and strengthened using prestressed CFRP laminate to evaluate the performance and the effectiveness of this technique. The experimental program consisted of testing 10 steel beams strengthened with bonded and unbonded prestressed CFRP laminate with and without mechanical end anchorage system. The results, failure modes and the observations of the experimental tests are illustrated and discussed. To predict the interfacial stress acting on the contact zone, an analytical model of beams with CFRP is developed. 4 beams are evaluated using the developed analytical model equations. A finite element analysis was conducted using the cohesive zone method (CZM) to extend the study. To verify the developed finite element model, the experimental tests results are compared to the finite element model outputs. The finite element model is used to evaluate the effect of increasing the prestressing level applied to the CFRP reinforcement. It was found that using the prestressed CFRP laminate with the mechanical anchorage system increases the overall strength of the beams, delays the premature debonding failure and enhances the serviceability of the composite section Key words: Steel Structure – CFRP – Prestressing – Mechanical Anchorage – CZM – Interfascial stresses