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

研究结果表明：1）通过对高应变率引起的脆性转变和尺寸效应的研究，探讨了在兵库县南部地震中受损钢筋混凝土结构的破坏机理和原因。首先，建立了速率相关弥散裂纹模型和粘塑性模型的有限元列式。其次，针对弥散裂纹模型的不足，提出了一种复合材料非连续分析的混合有限元方法。这些有限元模型的模拟结果表明，从弯曲到更脆，共享类型的失败的失败模式的过渡的可能性。研究了现有的钢筋混凝土结构设计方法和应变协调方法对FRP加固结构的适用性。确定了以下塌陷机制 关于我们 并分析：3）面对以下事实：（1）由于裂缝沿着FRP-混凝土界面的灾难性扩展，复合板与混凝土之间的粘结可能发生突然断裂;（2）FRP与混凝土界面沿着方向摩擦力较小或无摩擦力，这可能不同于混凝土与钢筋之间的粘结-滑移行为，提出了粘结模型，包括粘结应力-滑移关系。并讨论了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）。基于断裂力学的概念，建立了一个分析模型，即断裂能法。此外，对碳纤维布加固钢筋混凝土受拉构件进行了一系列的试验研究。试验变量包括高强和高模两种CFRP材料、不同混凝土强度、不同钢筋配筋率和不同FRP布层数。通过本试验方案，首次获得了最小裂缝间距、裂缝分布特征、裂缝宽度的板应力优势、脱粘长度等基本结论。5）作为一种通用的数值模型，本文建立了FRP片材加固混凝土结构的有限元模型，用于分析FRP片材加固混凝土结构在不同破坏模式（弯曲破坏、剪切破坏和剥离破坏）下的承载力和变形性能。该模型能较好地反映梁、柱、隧道等构件的极限承载力。6）通过一系列试验研究了FRP加固法中FRP片材-混凝土界面在不同环境作用下的耐久性、界面性能、界面粘结强度、7）提出了将剥离破坏作为设计指标之一的设计概念，认为通过本研究建立的理论体系是合理的，并将在今后的研究工作中得到发展。所获得的新发现被认为对于建立合理的设计规范是有用的。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