Nonlinear Finite Element Analysis of Steel Fiber Reinforced Concrete Beams Subjected to Pure Torsion

Abstract

Steel fiber reinforced concrete (SFRC) can enhance post-cracking tensile resistance through fiber bridging across cracks; however, the torsional contribution of fibers is still not explicitly addressed in most design provisions. This study develops a three-dimensional nonlinear finite element (FE) model in ABAQUS to evaluate the response of SFRC beams subjected to pure torsion. The concrete response was simulated using the Concrete Damage Plasticity (CDP) model, while the tensile softening behavior of SFRC was represented using stress–crack opening displacement relationships derived from experimental material characterization data. The FE model was validated against two independent experimental programs reported in the literature, covering beams with different fiber contents and transverse reinforcement ratios. The validation was performed through comparisons of torque–twist response, ultimate torsional capacity, and crack patterns. Following validation, a parametric study was conducted to examine the effects of SFRC post-cracking tensile softening behavior, concrete compressive strength, stirrup bar diameter, and stirrup spacing. The results showed that SFRC tensile softening behavior significantly influenced residual torsional resistance, deformation capacity, and post-cracking response. Increasing concrete compressive strength improved both cracking torque and ultimate torsional capacity, although the improvement was not directly proportional to the strength increase. Reducing stirrup spacing was more effective than increasing stirrup bar diameter because closer stirrups improved crack control and enhanced the torsion-resisting mechanism. The findings confirm that steel fibers and transverse reinforcement provide complementary contributions to torsional resistance under pure torsion.