Behavior of high-strength fibrous concrete slab–column connections under gravity and lateral loads

Ten slab–column connections were tested under combinations of gravity and lateral loads to investigate the effect of adding steel fibers to concrete mix on the structural behavior of normal- and high-strength slab–column connections. The variables selected for this study were the strength of concrete, volumetric ratio of steel fibers, type of steel fibers, and moment to shear ratio. The test specimens consisted of two identical series. The first series constructed with normal-strength concrete with a cube compressive strength of about 28 MPa, and designated as NSC. The second series constructed with high-strength concrete with cube compressive strength of about 75 MPa were designated as HSC. Each series consisted of three specimens with steel fibers and were tested under gravity load and unbalanced moment, and two control specimens; one was tested under gravity load only, while the other was tested under pure moment. The addition of steel fibers does significantly enhance the performance of the tested slab; it improves the shear strength, increases the ductility due to deflection and rotation, yields greater stiffness, and smaller cracks widths. Further improvement was also obtained when larger aspect ratio was used. Test results showed that the high-strength concrete specimens had larger shear strength, displacement and rotation ductility ratios, and corresponding energy absorption, than the normal-strength specimens by about 7–21%, 11–64%, 106–123%, 48–150%, and 93–246%, respectively. Incorporating steel fibers with high-strength concrete improved the overall deformation characteristics of the tested specimens and resulted in less sudden and more gradual failure mode.