Finite Element Method (FEM) models of Reinforced Concrete (RC) beams strengthened in flexure using prestressed Near-Surface Mounted (NSM) Carbon Fiber Reinforced Polymer (CFRP) subjected to quasi-static loading were developed and presented in this paper. One un-strengthened RC beam and four RC beams strengthened using NSM CFRP prestressed to various prestress levels were modeled. Comparisons of the load-deflection behaviors between the FEM models and the experimental test results indicate the good agreement in the loading branch. However, differences in the stiffness exist once the beams are unloaded. It seems that the concrete damage variables in tension and in compression play a paramount role in the response of the beams under cyclic loading. The possible modifications to the developed FE model are outlined as well as the future needed research.

The structural response of reinforced concrete (RC) girders strengthened with fiber reinforced polymer (FRP) composites in shear is investigated in this study, using a rationally-developed three-dimensional finite element model that was calibrated through comparison with test results. Analysis of reinforced concrete structures dominated by shear requires careful consideration in selecting the appropriate elements and material models. This task is more prominent in RC girders strengthened with FRP composites due to the difficulties of characterizing the corresponding properties and failure modes. Thus, the novel attributes of the proposed model is in the description of the three-dimensional constitutive material laws for each component. In the proposed model, the softening behavior of concrete under a triaxial state of stress was accounted for. The effect of the out-of-plane stress behavior of the FRP-concrete interface was carefully evaluated, which currently cannot be measured during experiments. In addition, the use of mechanical anchors to improve the bond behavior was properly simulated. Furthermore, the damage mechanism and progression of failure were carefully monitored. The model was shown to provide a good level of correlation with experimental data, and could therefore be used to conduct extensive parameter studies.

Fiber-reinforced Polymer (FRP) started to find its way as an economical alternative material in civil engineering from the early 1970s. The behavior and failure modes for FRP composite structures were studied through extensive experimental and analytical investigations. While research related to the flexural behavior of FRPstrengthened elements has reached a mature phase, studies related to FRP shear strengthening is still in a less advanced stage. In all proposed models to predict the shear capacity, the constitutive behavior of concrete and FRP was described independently. The true behavior, however, should account for the high level of interaction between the two materials. In this research, new constitutive relations for FRP-strengthened reinforced concrete elements subjected to pure shear are developed. In order to generate these relations, large-scale tests of a series of FRPstrengthened reinforced concrete panel elements subjected to pure shear are conducted. The University of Houston is equipped with a unique universal panel testing machine that was used for this purpose. These constitutive laws are implemented into fiber-based finite element models to predict the behavior of externally bonded FRP strengthened beams. The newly developed model proved to provide a good level of accuracy when compared to experimental results.

Fiber reinforced polymers (FRP) is an attractive material to the field of strengthening and confining new and existing structures. FRP is usually used to wrap columns to increase the ultimate strength and strain of the concrete through confinement. Existing columns typically have spiral steel reinforcement (SS) in the section when wrapped with FRP. The nature of the problem becomes totally different since there are two systems with different behavior engaged in confinement. Several models were proposed to depict the behavior of the FRP alone in confining concrete. On the other hand, the literature has limited studies assessing the behavior of FRP and SS working on confining concrete simultaneously. This paper proposes a model addressing the two materials engagement in circular columns. The development of the effective lateral confinement pressure is based on Lam and Teng model for FRP action and Mander Model for SS action. It also introduces the force eccentricity as a new parameter that plays an important role in estimating the amount of confinement involved. Hence, the level of strength and ductility vary based on the eccentricity. The proposed model considers the fully confined curve as an upper bound curve with zero eccentricity and the unconfined curve as a lower bound curve with infinite eccentricity. In between these two curves, infinite numbers of stress-strain curves can be generated based on the eccentricity. Generalization of the moment of area approach is utilized based on proportional loading, finite layer procedure and the secant stiffness approach, to achieve equilibrium points of P-e and M-f diagrams up to failure. Finally the model is validated by showing good conservative correlation to experimental data.

The increasing demand to strengthen existing infrastructure has resulted in growing popularity of advanced fiber composite materials (FRPs) applied to reinforced concrete (RC) members as externally bonded reinforcement. Although FRPs contain very high tensile strengths, premature debonding usually prevents the material from reaching its full potential. Research is currently underway to address this shortcoming by the provision of anchorages to the ends of FRP reinforcement. Bi-directional fiber patch anchors have been found to be one of the most effective anchorages available, which are particularly suitable in shear strengthening applications. The ongoing need for verification of the various influencing parameters such as anchor size, spacing and fiber thickness have inspired further numerical and experimental studies resulting in the present work. The paper will investigate the effect of such parameters highlighting key relationships that may be applied for future use in anchorage strength models.