Kinematics-Based Modelling of Deep Beams Retrofitted with FRP Wraps

Abstract

Reinforced concrete deep beams are one of the most important elements used in civil engineering structures, not only because they are able to resist high compressive forces, but also because they can be used to increase the resistance of a structure under a dynamic loading. However, given that they are not exempt from degradation provoked by aging or unexpected loading, they tend to decrease in quality and resistance. To avoid this, Fiber Reinforced Polymers (FRP) appeared as one of the methods used for the strengthening of the deep beams. The main goal of this thesis is to introduce and define the fundamental theory of the Five-Spring model, developed by Mihaylov et al. (2015), and extend it to deep beams strengthened with FRP wraps. The extended Five-spring model will account the effect of the FRP wraps depending on the following parameters: (1) the bond-slip relationship of the FRP strip to the concrete interface; (2) the process of debonding of the FRP strip; (3) the angle of the critical shear crack ; (4) the ratio between the depth of the FRP strip and the depth of the beam; (5) the wrapping scheme ; (6) the position of the strip with respect to the critical shear crack and (7) the shape of the critical shear crack. To account for the bond-slip model and the process of debonding, models developed by Lu et al. (2005) and Chen et al. (2012) were selected, yet in a simple manner. The shape of the critical shear crack on the other side was accounted by analyzing what is the shape that produce the most accurate response of the process of debonding. Once the influence of the seven parameters was considered, they were implemented one by one in the Matlab code to validate this extended Five-spring model with experimental data. The extended Five-spring model was validated against test results from the literature and concluded that FRP has a positive effect in the pre-and-post peak behavior of deep beams. However, it was also observed that the accuracy of the predicted results would increase when more parameters, such as the concrete crushing around the loading plate, supports settlement or debonding of the FRP , were considered.