Abstract
Carbon fiber reinforced polymer (CFRP) composites have exhibited a great potential for strengthening of steel structures. In the current study, an innovative prestressed unbonded reinforcement (PUR) system is introduced for fatigue strengthening of existing steel members. The system relies on a pair of mechanical clamps; each holds multiple CFRP plates and anchors their prestressing forces to the steel substrate via friction. A finite element model was established to optimize the design of the required mechanical components of the system. A set of static and fatigue tests was conducted on the developed mechanical clamps as the key elements of the proposed PUR system. The performance of the PUR system was then evaluated using a set of fatigue tests on two precracked steel plate specimens, one without any strengthening system and the other one strengthened with the proposed PUR system. In the latter specimen, the CFRP plates were prestressed up to about 800 MPa (approximately 30% of the CFRP tensile strength), which resulted in a complete fatigue crack arrest in the precracked steel plate. Furthermore, neither slippage of the mechanical clamps nor any prestress loss in the CFRP plates was observed after 7.5 million fatigue cycles. Based on the promising experimental results, obtained from the sets of fatigue tests performed in the current study, it can be concluded that the proposed PUR system can be considered as an efficient alternative to the conventional bonded reinforcement solutions for fatigue strengthening of damaged steel members.
Highlights
Fatigue behavior of metallic members has been intensively studied in the past [1], and the efficiency of a number of conventional techniques for the strengthening of fatigue-prone structures have been experimentally investigated in the literature [2]
Experimental results strongly confirmed that the developed mechanical clamping system is capable of transferring the entire tensile capacity of the carbon fiber reinforced polymer (CFRP) plates to the steel substrate, even after experiencing 10 million fatigue cycles
The performance of the developed prestressed unbonded reinforcement (PUR) system for fatigue strengthening of cracked steel members was evaluated in a set of fatigue tests on precracked steel plate specimens
Summary
Fatigue behavior of metallic members has been intensively studied in the past [1], and the efficiency of a number of conventional techniques for the strengthening of fatigue-prone structures (such as drilling stop holes and/or application of bolted, riveted, or welded cover plates) have been experimentally investigated in the literature [2]. The results have shown that when metallic beams are strengthened by prestressed CFRP plates, the performance of the CFRP-strengthened steel beams is more sensitive to the magnitude of prestress level, rather than the presence of the bond [28,29]. The system consists of two sets of high performance mechanical clamps, which hold multiple prestressed CFRP plates, and transfer their prestressing forces to the damaged/cracked steel substrate to reduce the acting stress level in the member, and enhance its fatigue performance. The great performance of the developed system in terms of stress reduction in a CFRP-strengthened steel member was demonstrated through a set of fatigue tests on precracked steel plate specimens, with and without the proposed PUR system
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