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

外粘碳纤维布加固混凝土结构技术的建立

基本信息

批准号：
08555107
负责人：
WU Zhishen
金额：
$ 4.22万
依托单位：
Ibaraki University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08555107/
关键词：
Concrete Structures FRP Sheet-Strengthening Method Design of Debonding Shear Strengthening Fracture Mechanics Analysis Finite Element Analysis Effectiveness of Crack Control Durability Assessment 耐震補強工法炭素繊維シート剥離破壊破壊力学的構造解析法複合補強

项目摘要

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

作为研究结果，1)通过关注高应变率和尺寸影响导致的脆性转变，研究了兵库县南部地震损坏的钢筋混凝土结构的破坏机制和原因。其次，为了消除弥散裂纹模型的一些缺点，提出了复合材料不连续分析的混合有限元方法。模型显示了失效模式从弯曲失效转变为更脆的共享类型失效的可能性，并且表现出共享主导行为的结构失效可以通过所提出的有限元模型很好地表达。2）适用性研究了现有的钢筋混凝土设计方法，以及 FRP 加固结构的简单应变协调方法，确定并分析了以下倒塌机制：钢筋屈服-FRP 断裂、钢筋屈服-混凝土破碎、压缩破坏、共享破坏。 3) 面对以下事实： 1) 由于裂纹沿着 FRP-混凝土界面灾难性扩展，复合板和混凝土之间的粘结可能会突然断裂； 2) 较少或沿FRP-混凝土界面观察不到摩擦行为，这可能与混凝土与钢筋之间的粘结滑移行为不同，因此提出了包括粘结应力-滑移关系的粘结模型。还讨论了 I 型、II 型和混合模式（剥离）界面的临界应变能释放率（界面断裂能）。这些值是使用拉伸拉伸的双剪切样本测量的。分析模型，所谓的断裂能方法，是基于断裂力学的概念而开发的，并且对碳纤维片材增强的RC拉伸构件进行了一系列的实验研究，变量包括高强度和高模量的两种类型的CFRP材料。混凝土强度不同，该实验方案首次获得了钢筋配筋率、不同层数FRP板材的最小裂缝间距和裂缝分布特征、裂缝宽度的板材应力优越性、脱粘长度等重要发现。实验结果还用于校准几个材料参数。5）作为通用数值模型，1）中提出的有限元模型被开发用于评估FRP的承载能力和变形行为该模型可以很好地表达梁、柱、隧道等不同破坏模式下的钢筋混凝土结构的弯曲破坏、剪切破坏和脱粘破坏等最终行为。建议将CFRP片材的性能和复合材料结构行为相结合的设计策略，以有效和高效地利用CFRP片材。6)通过一系列实验研究了FRP加固方法中FRP片材-混凝土界面的耐久性7）提出了将脱粘失效作为设计指标之一的设计理念。通过这项研究构建的理论体系被认为是合理的，并将在未来得到发展研究工作所取得的新发现被认为对于建立合理的设计规范是有用的。