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

研究结果：1)以高应变率和尺寸影响下的脆性转变为研究重点，探讨了小谷县-南部地震破坏钢筋混凝土结构的破坏机制和原因。首先，通过安装速率相关的涂抹裂纹模型和粘塑性模型，建立了有限元公式。其次，为了消除涂抹裂纹模型的缺陷，提出了一种用于复合材料不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，破坏模式有可能从弯曲破坏模式过渡到更脆的共享破坏模式。所提出的有限元模型可以很好地表达具有份额支配行为的结构的破坏。2)研究了现有钢筋混凝土设计方法的适用性，以及一种简单的应变协调方法对frp加固结构的适用性。确定并分析了钢屈服- frp断裂、钢屈服-混凝土破碎、压缩破坏、共享破坏和不同的脱粘破坏机制。3)面对1)frp -混凝土界面裂缝突变扩展可能导致复合板与混凝土粘结突然断裂的事实；2)沿frp -混凝土界面可以观察到很少或没有摩擦行为，这可能与混凝土与钢筋之间的粘结滑移行为不同，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）。这些值是用双剪试样在拉力下测量的。基于断裂力学的概念，提出了一种断裂能分析模型。此外，还对碳纤维板加固钢筋混凝土受拉构件进行了一系列试验研究。变量包括高强高模两种CFRP材料、不同强度的混凝土、不同配筋率的钢筋、不同层数的FRP片材。通过该实验程序，首次得到了许多重要的发现，如最小裂纹间距和裂纹分布特征、裂纹宽度的板应力优势、脱粘长度等。实验结果也用于标定几个材料参数。(5)建立了1)中提出的有限元模型，作为一种通用的数值模型，对钢筋混凝土结构在受弯破坏、剪切破坏和脱粘破坏等不同破坏模式下FRP布增强混凝土的承载能力和变形行为进行了评估。该模型可以很好地表达梁、柱、隧道等不同结构构件的极限性能。最后，提出了一种综合碳纤维布性能和复合材料结构性能的设计策略，以有效地利用碳纤维布。6)采用不同环境作用、表面行为、环氧树脂类型和混凝土质量的试验方案，对FRP加固法中FRP板-混凝土界面的耐久性进行了研究。7)提出了将脱粘破坏作为设计指标之一的设计理念。通过本研究构建的理论体系是合理的，将在今后的研究中进一步完善。所取得的新发现被认为对建立一个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