FRP加固钢筋混凝土梁界面开裂分析

Analysis of interfacial cracking of RC beams strengthened with FRP

应用理论分析及有限元模拟和模型试验相结合的方法分析了FRP加固钢筋混凝土(RC)梁界面的开裂破坏规律。研究结果表明:FRP加固RC梁界面开裂可以应用断裂力学的方法解析,理论分析结论与有限元模拟结果一致。在FRP的剥离角度较大时界面是Ⅰ型和Ⅱ型混合开裂;同时考虑到混凝土剪切裂缝上下错动的尺寸与构件的尺寸相比很小,FRP-RC梁界面主要表现为Ⅱ型断裂。界面的应力强度因子随着加载的增加分为三个发展阶段,分别以混凝土开裂和钢筋屈服为分界点,界面的临界应力强度因子约为5.91MPa·m0.5。并结合试验给出了FRP的极限剥离应变,在工程应用中控制FRP应变在剥离应变以内可以有效地避免界面开裂破坏的发生。

Based on the theoretical analysis, the FEM simulation and a series of model tests, the cracking behaviors of FRP-concrete interface are analyzed. The results show that: the interfacial cracking of FRPstrengthened RC beams can be analytically calculated with the fracture mechanics method, and the theoretical solutions accorded well with the FEM results. The interfacial stress intensity factor of mode Ι is sensitive to the FRP debonding angle. When the FRP debonding angle is large the interfacial cracking is Ι and ΙΙ mixed-mode fracture, but considering that the alternate dimensions of shear cracks are quite little according with the member length, the interface of FRP strengthened RC beams mainly exhibites as mode Ⅱ cracking. The interfacial mode ΙΙ stress intensity factor is proportional to the square root of concrete strength or that of FRP stiffness, and increases linearly with the increase of FRP strain. In the model tests three evolution processes of the stress intensity factors along with loading are observed, in which the dividing points are the concrete cracking and the steel reinforcement yielding. The interfacial critical stress intensity factor is about 5.91MPa ·m0.5. At last the FRP debonding strain is given according to the tests, and the interfacial debonding can be effectively avoided by limiting the FRP strain in the range of the debonding strain.