Finite element analysis of RC beams strengthened with near-surface mounted reinforcement bars under pure torsion

Abstract

This study’s primary objective is to investigate the pure torsional behavior of reinforced concrete beams with inadequate resistance to applied loads. The beam needs to be strengthened with a simple and effective technique, the near-surface mounted. This paper was conducted to check the validity and accuracy of experimental results. This numerical study included testing three specimens; one was control beams, while the remaining were strengthened beams with two configurations with NSM closed and U-stirrups steel stirrups and longitudinal NSM bars. Each beam has three variables: Remove NSM longitudinal bars, use concrete’s compressive strength (20,60) MPa, and Strengthen with NSM GFRP and CFRP bars. All beams have a cross-section (300x300 mm), and the length of the beam was constant (2100 mm). The numerical analysis showed close results to those obtained from the experimental work. This convergence was evident in failure and ultimate torque patterns and mechanisms. The ultimate torque increased when strengthening with four faces of NSM closed stirrups and three faces of NSM stirrups (U-shape) at a spacing of 130mm. On the other hand, The increase in compressive strength leads to an increase in the ultimate torque. Lowering compressive strength leads to more ductile behavior with lower ultimate torque. Removing the additional longitudinal reinforcement has a minor effect on behavior. The type of bars, steel, CFRP, and GFRP, have a marginal impact on the behavior with more ductile behavior for the steel reinforcement bar beams.