Establishment of strengthening technique for concrete structures with externally bonded Carbon Fiber Sheets

作为研究成果，1)重点研究了高应变率和尺寸效应引起的脆性转变，探讨了地震中受损钢筋混凝土结构的破坏机理和原因。首先，建立了基于率相关的弥散裂纹模型和粘塑性模型的有限元模型。其次，为了克服弥散裂纹模型的一些缺陷，提出了复合材料不连续分析的混合有限元方法。用这些有限元模型的模拟结果表明，破坏模式有可能从弯曲破坏模式转变为更脆性的共享破坏类型。2)研究了现有钢筋混凝土设计方法的适用性，提出了一种适用于FRP加固结构的简单应变协调方法。以下崩溃机制被确定为…3)针对1)复合板与混凝土之间的粘结可能会突然断裂的事实，这是由于裂缝沿FRP-混凝土界面的灾难性扩展所致；2)在FRP-混凝土界面上观察到较少或没有摩擦行为，这可能不同于混凝土与钢筋之间的粘结滑移行为，本文提出了考虑粘结应力-滑移关系的粘结模型。讨论了I型、II型和混合型(剥离)界面的临界应变能释放率(界面断裂能)。根据断裂力学的概念，建立了一个分析模型，称为断裂能法。此外，还进行了碳纤维布加固钢筋混凝土受拉构件的一系列试验研究。试验变量包括两种高强高模CFRP材料、不同混凝土强度、不同配筋率、不同层数的FRP片材。该试验程序首次获得了最小裂缝间距、裂缝分布特征、裂缝宽度对板材应力的优势、剥离长度等一系列基本结论。5)将文[1]中提出的有限元模型作为通用的数值模型，对FRP片材加固钢筋混凝土结构的受弯破坏、剪切破坏和剥离破坏等破坏模式的承载能力和变形性能进行了评估。该模型能较好地表达梁、柱、隧道等不同结构构件的极限性能。6)通过一系列不同环境作用、表面性能、环氧树脂种类和混凝土质量的试验方案，对FRP加固方法中FRP板-混凝土界面的耐久性进行了研究。7)提出了将剥离破坏作为设计指标之一的设计思想，通过本研究构建的理论体系是合理的，并将在今后的研究工作中得到进一步发展。这些新发现被认为对制定合理的设计规范是有用的。较少

As the research result,1) The failure mechanism and reason of damaged reinforced concrete structures by Hyogoken-Nanbu earthquake is investigated by focusing on brittleness transition due to the high strain rates and size affect. Firstly, a finite element formulation is developed by installing both rate-dependent smeared crack model and viscoplastic models. Secondly, in order to remove some drawbacks of smeared crack models, a mixed finite element method for composite discontinuous analysis is proposed. The simulation results with these FEM models show the possibility of a transition in the mode of failure from flexural to a more brittle, share type of failure. And failure of structures that exhibit a share-dominated behavior can be expressed well by the proposed finite element models.2) Applicabilities of existing reinforced concrete design method, and a simple strain compatibility methods to FRP-strengthened structures are investigated. The following collapse mechanism are identified … More and analyzed : steel yield-FRP rapture, Steel yield-concrete crushing, compressive failure, share failure and different debonding failures.3) Facing on the facts that 1) the bond betweet the composite sheet and the concrete may fracture in a sudden manner as the result of the catastrophic propagation of a crack along the FRP-concrete interface ; 2) less or no frictional behavior along the FRP-concrete interface can be observed, which may be different from the bond-slip behavior between concrete and reinforcing bars, bonding model, including bond stress-slip relationship is proposed. And the critical strain energy release rate (interfacial fracture energies) for the interface for mode I,mode II and mixid mode (peeling-off) is also discussed. The values are measured using double-shear specimens pulled in tension.A analytical model, so called fracture energy approach, is developed based on the concept of fracture mechanics. Moreover, a series of experimental investigations of RC tensile members strengthened by carbon fiber sheets is performed. The variables included two types of CFRP materials with high strength and high modulus, different strengths of concrete, different reinforcing ratios of rebars, and different layrs of FRP sheets. A lot of essential findings, such as the minimum cracking spacing and crack distribution characteristics, superiority of sheet stress of crack width, and debonding length etc.are conducted firstly by this experimental program. The experimental results is also used to calibrate the several material parameters.5) As a general numerical model, the finite element model proposed in 1) is developed to evaluated the load-carrying capacity and deformation behavior of FRP sheet-strengthened concrete of RC structures with different failure modes, such as flexural failure, shear failure and debonding failures. The ultimate behavior for different structural members such as beams, columns and tunnels etc, can be expressed well by the model. Finally, a design strategy integrating the properties of CFRP sheets and composite structural behavior is recommended to effectively and efficiently utilize the CFRP sheets.6) The durability of FRP sheet-concrete interface in FRP-strengthening method is investigated by a series of experimental program with different environment actions, surface behavior, types of epoxy and concrete qualities.7) A design concept for debonding failure as one of design indices is suggested.The theoretical system constructed through this research is considered to be rational and will be developed in future research effort. The achieved new findings is considered to be useful for establishment of a rational design code. Less