Finite Element Modelling of Different Strengthening Strategies for Reinforced Concrete Deep Beams

Abstract

Reinforced concrete deep beams are important structural elements, which transmit loads from the upper structure to widely spaced lower supporting elements. By definition, such members have small shear-span-to-depth ratios and their behavior is governed by shear. Because some deep beams have suffered degradation in existing buildings and bridges, Fiber Reinforced Polymer (FRP) or Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) can be used for their retrofit. The main goal of this thesis is to use advanced nonlinear finite element models in order to understand the behavior of deep beams retrofitted with FRP sheets and UHPFRC layers. For this purpose, general information about the behavior of FRP and UHPFRC is gathered and summarized. The selected approach for modelling is a smeared rotating crack as formulated in the Modified Compression Field Theory for elements subjected to shear. Nonlinear finite element analyses are performed on selected experimental studies using program VecTor2. The predictions of the finite element models are compared to the test results in order to validate the model. It is shown that the finite element models capture adequately both load-displacement curves and failure loads of the test specimens. Using the validated models, a parametric study is performed in order to investigate the effect of FRP sheets and UHPFRC layers on the behavior of true-scale deep beams. The variables considered were the shear-span-to-depth ratio, the layout of FRP sheets, the fiber volume ratio and thickness of UHPFRC layers. The results are compared to identify effectiveness of the two retrofitting strategies and conclusions are drawn.