Development and Application of Composite Beam Theory on FRP Reinforced Concrete Flexural Members
Type of DegreePhD Dissertation
Civil and Environmental Engineering
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Although there are specifications and approaches for the design of concrete flexural members reinforced with FRP, most of them were derived from empirical data. In order to obtain the rigorous theoretical definition of the fundamental mechanics associated with partial composite action between concrete and the FRP reinforcement, the practical and theoretical issues that must be further addressed. Therefore the overall goals of this research were to develop the needed theory and demonstrate its accuracy and application. This study firstly developed a new method to establish an analytical solution for determining the transfer length for FRP tendons in prestressed concrete. The governing equations were derived by combining the local bond-slip relationship for FRP tendons in concrete with composite beam theory. Comparisons to test data strain results demonstrated that the predicted results were accurate. Subsequently, based on the developed method, the difference between sequential release and simultaneous release of tendons in the manufacturing process of pretensioned concrete members was further discussed. The mechanical response analysis of coupling between longitudinal and transverse interactions was also investigated for concrete beams strengthened with externally bonded FRP laminates using composite beam theory. Associating with the bond stress-slip relationship between FRP laminates and concrete, two sets of governing equations were derived to determine the interfacial stresses. Comparisons between the developed model with published finite element results and existing analytical solutions in the literature confirmed the feasibility and accuracy of this novel approach. A parametric study was also carried out to investigate the effect of various factors on the interfacial behavior of externally bonded FRP for strengthening concrete beams. Finally, a novel finite element (FE) modeling approach was developed to further verify the developed theoretical method. The present FE model took into account the friction coefficients obtained from pull-out tests on the FRP tendons and prestressed concrete members. Convergence analysis of two numerical simulations with different mesh densities was carried out as well. The consistency between the analytical solution and FE simulation not only further proved the reliability of composite beam theory, but also demonstrated the importance of the bond-slip relationship in fully understanding the mechanical properties of concrete members reinforced by FRP systems.