基于内聚力模型的FRP布加固混凝土梁柱子结构受力性能分析

FRP-混凝土界面力学性能是影响FRP加固结构承载力的重要因素。建立了可模拟FRP布加固结构黏结界面非线性软化力学行为的双线性内聚力单元，考虑混凝土与钢筋的材料非线性，进行了FRP布加固混凝土梁柱结构静力加载全过程有限元分析。分析了FRP布及黏结界面的应力变化、界面与结构破坏机制以及结构的承载力，与试验以及不考虑界面黏结滑移的有限元分析结果进行了比较，以验证方法的合理性，并提出了改进FRP环形箍布置方式。有限元分析结果表明：FRP布的拉应力、黏结界面应力与损伤变量等呈现节点区域大、跨中小的分布特点，剥离破坏随加载过程由节点域向跨中扩展，混凝土开裂后，FRP布与钢筋共同构成了悬链线机制；有限元分析所得结构破坏过程与试验的基本一致，揭示了黏结界面退化对FRP布加固混凝土结构受力性能的影响，所得各阶段最大荷载与试验结果的相对误差小于5%；不考虑黏结界面性能的退化与FRP布的剥离，则高估了悬链线阶段FRP布的贡献以及加固结构的承载力。黏结界面内聚力模型可为FRP布加固框架结构的受力性能分析提供参考。

Analysis on mechanical properties of FRP retrofitted concrete beam-column structure using cohesive model

The mechanical properties of the bonding interface between the FRP sheet and the surface of concrete structures are important to the bearing capacity of the FRP-retrofitted concrete structures. By using the bilinear cohesive constitutive model, the cohesive element to simulate the nonlinear softening mechanism of the bonding interface is proposed. The loading process of the FRP-retrofitted beam-column structure were simulated by finite element method in which the cohesive elements for the bonding interface were combined with the separated nonlinear elements of concrete and steel bars. The stress of FRP sheet, shear stress and slipping of the bonding interface, failure mechanism and bearing capacity of the retrofitted beam-column structure were analyzed numerically. The simulated results were compared with the results by model tests and by other FEM in which the bond-slip of the interface was ignored. According to the numerical analysis results, the tensile stresses of FRP sheet, bonding stresses and the damage parameter in the interface are larger at the beam-column joint than those at the mid-span of the beam. The peeling of the FRP sheet from the concrete cover starts at the beam-column joint and was extended to the mid-span of the beam with the loading. After the cracking of the concrete cover, the loading is balanced by both of the FRP and steel bar in catenary way. This simulated mechanism and damage phenomena are in good accordance with those obtained by the model tests. The accuracy of the presented simulating method is proved by small relative errors (lower than 5%) of the ultimate bearing capacity of the retrofitted beam-column structure between the simulated results and the model tests. By comparison with the results of the presented adhesive finite element model, the finite element analysis model in which the softening and slipping of the bonding interface are ignored, would result in an over-estimated contribution of the FRP sheet to the catenary action and the ultimate bearing capacity of the retrofitted structure. It is shown that the proposed adhesive model for the boding interface is an effective and practicable method for the analysis of FRP retrofitted structures.