梯度锚固预应力NSM CFRP板条加固梁破坏模式与影响因素试验研究

为探索梯度锚固预应力表层嵌贴(Near Surface Mounted,NSM) CFRP板条加固梁的破坏模式,完成了1片普通预应力和7片梯度锚固预应力加固梁的弯曲性能试验,研究了端部梯度锚固设置、加固长度、混凝土保护层厚度和钢筋表面特性对结构力学性能的影响,分析了加固梁的破坏模式、特征荷载、延性、预应力和外荷载作用下...

Experimental Study on Failure Modes and Influence Factors of RC Beams Reinforced with Gradually Anchored Prestressed Near-surface-sounted Carbon-fiber-reinforced Polymer

A gradually anchored prestressed method for beams reinforced with near-surface-mounted (NSM) carbon-fiber-reinforced polymer (CFRP) strips is proposed. Bending tests of one ordinary prestressed reinforced beam and seven gradually anchored prestressed reinforced beams were completed, and the effects of the gradient prestress, reinforcement length, concrete protective layer thickness, and round bar on the mechanical properties of the structure were studied. The failure mode, characteristic load and ductility of the reinforced beam, and bonding stress of the fiber-reinforced polymer (FRP)-concrete interface under prestress and external load were analyzed. The crack spacing of the reinforced beam was calculated according to the Chinese structural design code GB 50010-2010, industry technical standard CTT/T 280-2018, and American Concrete Institute code ACI 440.1R-15. The results show that the gradually anchored prestressed reinforcement is superior to ordinary pre-stressed reinforcement in restraining fracture development, delaying the yield of longitudinal reinforcement, improving the bearing capacity of the reinforced beam, and avoiding end concrete cover separation. The bending capacity of the strengthened beam was significantly improved up to 35.48%; the ductility of the strengthened beam was greatly improved; and the failure deflection was increased by up to 100.33%. The performance of the reinforced beam increased with an increase in the end gradually anchored prestressed length. When the end gradually anchored prestress is set the same, reducing the total length of reinforcement, increasing the thickness of the protective layer, and using plain round reinforcement can reduce the bearing capacity of the reinforced beam. However, the surface characteristics of the reinforcement only affect the performance of the reinforced beam after the fracture exhibits horizontal branching. The peak value of the bond stress caused by the prestress and external load is within 400 mm of the FRP end. The fracture spacings calculated by GB 50010-2010 and ACI 440.1R-15 are slightly unsafe. The calculation results of CTT/T 280-2018 are conservative. Based on the crack spacing correction formula proposed in GB 50010-2010, by considering the influence of the FRP bond length, prestress of the gradient anchored, and thickness of the protective layer, the CFRP stress can be calculated more accurately when the protective layer of the concrete cover is separated.