Non-linear finite element analysis for the verification and parametric study of reinforced concrete beams strengthened in compression zone to improve ductility by using ABAQUS

Ductility is an important mechanical property of concrete structures, in tensile members, as it is the property that allows the structural member to deform plastically long before the failure point. To increase the deformation period of the beams, i.e., the ductility of failure. In the current paper, four reinforced concrete beams were modeled and compared using nonlinear finite element analysis. Reinforced concrete beams are developed and analyzed by using ABAQUS commercial software. Nonlinear material behavior, as it relates to steel reinforcing bars and plain concrete, is simulated. The effect of the change of the concrete compressive strength in the upper one-third of the beams on the ductility, the ultimate strengths, and the mode of failure of beams are investigated. One of the beam specimens was used as a reference. The change in the compressive strengths in the compressive zone was in the range of 27, 31, 37, and 42 MPa. The results of the analysis of the modeled beams were validated and compared with beams tested experimentally by previous researchers. It was found that load-deflection curves of the FE modeling of the beams match the same findings in the experiments. Furthermore, to investigate different techniques in strengthening the upper third of the beams for enhancing ultimate strength and ductility behavior, a parametric study was performed by modeling beam specimens consisting of two groups, among them using a hybrid of Carbon nanotubes (CNTs) & steel fiber, which was added to the concrete mixture of the upper third of a beam specimen and was used as strengthening layer stuck to the top layer of the compression zone of another beam. It was found that the beam that was strengthened in the compression zone by the layer of the concrete containing the mixture of the CNTs & steel fibers increased the beams' strength and ductility; hence, the ultimate load and deflection were increased by 63%, and 40%, respectively.