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

(1)不同纤维板的基本混杂设计通过考察不同纤维混杂层合板的初始刚度、抗折强度、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，明确了不同纤维混杂层合板的需求、要求和争议点。在此基础上，提出了采用三种超高模高强碳纤维板、两种不同模数芳纶纤维板、PBO纤维板和高断裂应变玻璃纤维板等不同用途的混杂FRP层合板的设计方法。此外，还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，对…进一步阐述了如何缓解纤维连续断裂引起的应力集中。此外，还进行了拉伸试验，验证了具有较高吸能能力的PBO纤维对缓解应力集中的效果。(3)混杂纤维布加固受压和受弯构件的试验和数值研究设计的混杂纤维布用于普通混凝土和钢筋混凝土梁的受弯加固，并从刚度、强度、延性和抗裂性等方面对相应的加固效果进行了定性评估。此外，通过一系列混凝土圆柱体试件的试验，研究了不同的配筋率(缠绕纤维布的间距)和混凝土强度等变量对加固效果的影响。(4)FRP与混凝土界面粘结性能及破坏机理研究首先，推导了FRP加固钢筋混凝土棱柱粘结承载能力的解析公式。(5)设计方法和有限元模型的建立通过上述分析和数值研究，对现有的预测界面剥离破坏的分析方法进行了改进，以评估混杂纤维布加固结构的剥离性能。然后制定了一个全面的设计准则，以包括所有可能的破坏模式，如钢屈服-玻璃钢断裂，混凝土压碎，剪切破坏和各种剥离破坏。(6)混杂纤维布加固钢筋混凝土结构的优化整体设计为了进一步发展混杂纤维布加固钢筋混凝土结构的混杂设计思想，进行了一系列的试验和数值研究，探讨了在不同的结构性能(如初始刚度、屈服和极限荷载等)下，如何实现加固结构的结构完整性，以及在纤维渐进断裂引起的荷载下降控制下结构延性的对策。通过这些研究，提出了混杂纤维增强布加固结构的优化设计方法。较少

(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