Experimental and numerical study of tubular steel columns with/without demountable bolted shear connectors embedded in the concrete

Three push-out specimens were experimentally tested to investigate the behavior of tubular steel columns (TSC) with and without bolted shear connectors embedded in normal concrete (NC). Each specimen consisted of a tubular steel column (TSC) encased in a 250 × 250 × 200 mm concrete cube The embedment/the prominent height of TSC was 100 mm. Foam was used underneath the TSC to form free space. The study considered variables such as the presence of demountable shear studs and reinforcement. The failure modes, load-slip response, peak load/slip, and shear stiffness of the specimens were analyzed. Furthermore, a finite element model (FEM) was developed using ABAQUS software to simulate the behavior of the tested specimens and validated against the experimental results. The FEM was also employed to conduct further parametric investigations. The results indicate that demountable shear studs significantly improve shear capacity, with specimens exhibiting a 217% higher peak load than those without studs. Reinforcing the concrete block had a negligible effect on peak load but increased peak slip by 37.7% and shear stiffness by 18.7% compared to the unreinforced specimen. Furthermore, increasing the TSC thickness significantly enhances peak load, with a 154.31% increase observed as the thickness increases from one-third of the bolt diameter to the full bolt diameter. Additionally, using TSC thicknesses greater than half the bolt diameter helps prevent bearing failure. Increasing the concrete compressive strength from 25 to 50 MPa leads to a 24.6% increase in peak load, while slip capacity decreases by 19.77%. For applications requiring high ductility, excessively high-strength concrete should be avoided, as it reduces slip capacity. The results also demonstrate that the bolt diameter should not exceed twice the TSC web thickness to prevent bearing failure.