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

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(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