Experimental / Theoretical Study on Strengthening effect enhancements of RC Structures with Hybrid FRP Laminates

(1)不同纤维混杂层合板的基本设计通过对不同纤维混杂层合板的初始刚度、断裂强度、极限强度和延性等设计指标以及应变硬化特性和纤维连续断裂引起的应力降等控制指标的研究，明确了不同纤维混杂层合板的需求、要求和存在的问题。在此基础上，针对不同用途，提出了超高模量、高模量、高强度3种碳纤维布、2种不同模量的芳纶纤维布、PBO纤维布和高断裂应变玻璃纤维布混杂FRP层合板的设计方法。并编制了相应的设计程序。(2)纤维断裂冲击应力集中的实验和理论研究为了改进上述基本的混合设计，本文进行了一个分析， ...更多信息 探讨如何消除纤维连续断裂引起的应力集中。此外，还进行了拉伸试验，以证明具有较高能量吸收能力的PBO纤维对消除应力集中的效果。(3)混杂纤维布加固混凝土受弯构件的试验与数值研究将设计的混杂纤维布用于普通混凝土梁和钢筋混凝土梁的抗弯加固，并从刚度、强度、延性和抗裂性等方面对加固效果进行了定性评价。此外，一系列的混凝土圆柱体标本包裹拟议的混杂纤维布被用来调查约束效应，通过改变不同的变量，如增强率（包裹纤维布带的间距）和混凝土强度等。(4)沿着FRP与混凝土界面粘结性能及破坏机理研究首先，推导了FRP与混凝土棱柱体粘结承载力的解析计算公式。在大量试验研究的基础上，通过理论分析和数值计算，对不同混杂纤维布加固钢筋混凝土受弯构件的粘结与剥离机理进行了深入研究。(5)设计方法和有限元模型的建立通过以上的分析和数值研究，改进了现有的界面剥离破坏分析方法，使之适用于混杂纤维布加固结构的界面剥离性能分析。一个全面的设计准则，然后开发，包括所有可能的失效模式，如钢屈服FRP断裂，混凝土破碎，剪切破坏和各种剥离故障。此外，本构模型的基础上建立的实验结果，以模拟纤维的渐进断裂在混杂纤维片材，从而实现非线性有限元分析，以评估两个破坏过程所造成的纤维的渐进断裂和混凝土开裂。(6)混杂纤维布加固钢筋混凝土结构的优化与一体化设计为了进一步发展混杂设计的概念，本文进行了一系列的试验和数值研究，以探讨在纤维渐进断裂引起的受控荷载跌落下，不同结构性能（如初始刚度、屈服和极限荷载以及结构延性）下，加固结构实现结构完整性的对策。通过这些研究，提出了混杂纤维布加固结构的优化设计方法。少

(1) Basic Hybrid Design of Different Fiber SheetsThe needs, requirements and points at issue on hybrid laminates by hybridizing different fibers are cleared up through investigating different design indices such as initial stiffness, rupture strength, ultimate strength and ductility and control indices such as strain hardening characteristics and stress drop due to successive fiber rupture. Based on these achievements, the design methods of hybrid FRP laminates by using different fibers such as three types of carbon fiber sheets with superhigh modulus, high modulus and high strength, two types of aramid fiber sheets with different moduli, PBO fiber sheet and glass fiber sheet with high rupture strain are proposed for different purposes. Moreover, the corresponding design program is also coded.(2) Experimental and Theoretical Investigations on Believing of Stress Concentrations due to Fiber Rupturing ImpactsIn order to improve above basic hybrid design, an analysis is performed to inves … More tigate how to relieve the stress concentrations induced by successive rupture of fibers. In addition, some tension tests were conducted to demonstrate the effect of PBO fibers with higher ability of energy absorption for relieving stress concentrations.(3) Experimental and Numerical Investigations on Strengthening Effects in Compressive and Flexural Concrete Members Strengthened with Hybrid Fiber SheetsThe designed hybrid fiber sheets are used to flexurally strengthen plain and reinforced concrete beams and the corresponding strengthening effects are qualitatively evaluated in terms of stiffness, strength, ductility and crack resistance. In addition, a series of concrete cylinder specimens wrapped with the proposed hybrid fiber sheets is used to investigate the confinement effects through varying different variables such as reinforcing ratios (spacing of wrapped fiber sheet strips) and concrete strength, etc.(4) Investigations on Interfacial Bond Behavior and Failure Mechanism along FRP and Concrete interfaceFirst, analytical equations are derived for predicting the bond carrying capacity in RC prisms bonded with FRP sheets. Based on a lot of experimental observations, both analytical and numerical analyzes are performed to give a clear insight into the bonding and debonding mechanisms in RC flexural members strengthened with different hybrid FRP sheets.(5) Establishments of Design Method and FE ModelThrough above analytical and numerical investigations, an existing analytical approach for predicting interfacial debonding failure is modified for evaluating the debonding behavior of strengthened structures with hybrid fiber sheets. A comprehensive design guideline is then developed to include all the possible failure modes such as steel yielding-FRP rupture, concrete crushing, shear failure and various debonding failures. Moreover, a constitutive model is established on the basis of experimental results to simulate the progressive rupture of fibers in hybrid fiber sheets and thus a nonlinear FE analysis can be implemented to evaluate both failure progresses caused by progressive rupture of fibers and cracking of concrete.(6) Optimum and integrated Design of RC Structures strengthened with Hybrid Fiber SheetsTo further develop the hybrid design concept, a series of experimental and numerical investigations is conducted to discuss countermeasures of realizing structural integrity of strengthened structures on different structural performances such as the initial stiffness, yield and ultimate loads and structural ductility under controlled load drops caused by progressive fiber ruptures. Through these investigations, an optimum design method on structures strengthened with hybrid FRP sheets is also proposed. Less