This paper presents Finite Element (FE) model to predict and analyze the cyclic loading response of reinforced concrete (RC) beams strengthened in shear with Carbon Fiber Reinforced-Polymer (CFRP) and Near-Surface Mounted (NSM) reinforcement. Four FE models were developed based on experimental tests conducted in a previous study. The first specimen was unstrengthened to serve as a control beam while the other two beams were strengthened with NSM CFRP bars with different spacing arrangements. The last beam specimen was strengthened with larger diameter CFRP bars. The developed FE models employed different nonlinear constitutive material modeling laws and techniques such as concrete cracking, steel yielding, bondslip between CFRP bars and epoxy resin, and debonding between the epoxy resin and concrete surfaces. The predicted and measured load-deflection response envelop curves along with the associated hysteresis loops for each specimen were used as platforms to validate the accuracy of the developed models. The results indicate that there is a good match between the predicted results and measured data. It is concluded that the developed FE model is a suitable tool to predict the behavior of such strengthening systems when subjected to cyclic loading and could be used in lieu of expensive experimental testing especially in design-oriented parametric 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.

This paper explores the investigation using finite element methods of experimentally tested hybrid FRP-UHPC (Ultra-High Performance Concrete) beams under flexural loading. A combination of mesh sensitivity and cohesive element parameter studies were performed through validation with experimental data. Good correlation was found between experimental findings and the finite element method, though higher stiffness was found in the latter case. It was found that an overall mesh size of 12.5 mm (0.50 in) was suitable for use in the model in order to allow for proper convergence. For the parameters at the GFRP-UHPC interface, it was found that a bond-slip ratio of 5 along with a bond strength of 5 MPa (0.725 ksi) were the best fit to experimental data and should be used in future studies. Additional investigation into the incorporation of considerations to allow for more damage accumulation in the finite element model was recommended.

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.