Punching shear performance of composite CFST-RC slab systems: Experimental and numerical evaluation

• Experimental assessment of punching shear behavior in RC slabs supported by embedded square CFST columns. • Evaluation of multiple strengthening techniques including steel bolts, welded bars, hybrid systems, and prestressing. • Strengthening methods increased punching capacity up to 5.47 times and energy absorption up to 10.49 times. • Strengthened connections exhibited a clear transition from brittle punching to ductile failure modes. • A validated nonlinear finite element model accurately predicts the behavior of strengthened CFST–RC slab connections. The increasing use of concrete-filled steel tube (CFST) columns in modern construction highlights the critical need to understand and enhance punching shear resistance at RC slab-column connections. This study presents an experimental and numerical investigation into the punching shear behavior of square RC slabs supported by embedded square CFST columns, focusing on novel and adapted strengthening techniques. Thirteen RC slab specimens were subjected to concentrated loading from a central embedded CFST column stub. The study systematically evaluated the effectiveness of various strengthening methods, including embedded steel bolts with varying lengths, welded steel bars around the column perimeter, combined bolt and welded bar configurations, and the application of a prestressing system. The experimental results demonstrate that these techniques significantly enhance the punching shear capacity and modify the failure characteristics compared to the control slab. Strengthening methods successfully transitioned the behavior towards more ductile and energy-dissipating modes, characterized by more extensive crack patterns. Quantitatively, the ultimate punching load was increased by up to 5.47 times (achieving 75.53 kN), elastic stiffness by up to 2.24 times, and absorbed energy by a remarkable up to 10.49 times. Complementing the experimental program, a sophisticated finite element model is proposed to simulate the behavior of these strengthened connections. The numerical predictions show excellent correlation with the experimental results.