مقاله انگلیسی رایگان در مورد نوارهای CFRP برای افزایش عملکرد خمشی تیرهای RC – الزویر ۲۰۱۸

Strengthening of reinforced concrete (RC) structures is essential for increasing its load carrying capacity and serviceability requirements. Currently, many research works are ongoing on strengthening RC structural elements. Carbon fiber-reinforced polymer (CFRP) reinforcements are of high tensile strength, high stiffness, low weight, durable, resistance to creep and fatigue compared to current construction materials, and have been used extensively. However, CFRP reinforcements reported weakness due to its brittle failure mode [1]. Numerous techniques have been developed and used to strengthened existing structural elements. The most popular strengthening techniques are external bonded reinforcement (EBR) [2] and near surface mounted (NSM) [3]. In EBR technique, strengthening reinforcements are bonded at the tension face of the flexural member using epoxy resin or adhesive; while NSM technique involves insertion of strengthening reinforcement with adhesive on the grooves prepared on the surface of the RC members. However, the EBR-strengthened specimens predominantly fail by debonding and concrete cover delamination [4–۶]. Also, EBR plates are highly vulnerable to weather effect and have low fire resistance [7,8]. Costa and Barros [9] performed experimental, analytical, and numerical studies on the flexural strength of RC beams strengthened using NSM CFRP strips. NSM grooves were cut into the bottom arm of the steel stirrups and to avoid shear failure U-wrap with CFRP sheets was used. The failure modes of the strengthened specimens were premature shear and concrete cover separation. Jung et al. [10] investigated the experimental applicability of NSM technique for strengthening of RC beams using CFRP rods and strips. A mechanical interlocking grooves were used to prevent debonding failure of the NSM strengthened specimens. Sena-Cruz et al. [11] studied the efficiency of EBR, NSM, and mechanicallyfastened EBR technique for flexural strengthening of RC beams under static and fatigue loading. However, the NSM-strips strengthened specimen failed by premature rip-off of the FRP strips. The NSM technique also have some limitations: (i) needed adequate concrete cover, (ii) sufficient width of beam, (iii) necessary edge clearance, and (iv) clear spacing between the grooves [3]. Akter et al. [12] proposed the side near surface mounted (SNSM) strengthening technique to overcome the limitations of the NSM technique using steel and CFRP bars. The SNSM technique involves preparation of the grooves within the concrete cover at both sides (near the tension face) of the beam specimen using a special concrete saw and insertion of the CFRP bars with the application of the epoxy adhesive. Based on the experimental results, the SNSM strengthening technique significantly increased the first cracking, yield, and ultimate load carrying capacities of the beams by about 3.17, 2, and 2.38 times, respectively, compared with the control specimen, and notably improved the failure modes of the specimens. Shukri et al. [13] studied the flexural responses of precracked RC beam specimens strengthened with the SNSM technique using CFRP bars, and the experimental results were verified using analytical models. The pre-cracked specimens revealed similar failure modes and greater stiffness compared with the nonpre-cracked specimens.