Effect of Concrete Slab Gradation on the Shear-Carrying Capacity of the Headed Stud Shear Connector

Shear connectors play a crucial role in achieving composite behavior, and their utilization has expanded in recent decades owing to the efficiency of constructing composite structures. Headed stud (HS) connectors are commonly employed for their role in establishing composite action, with connector strength being pivotal to overall connection effectiveness. This research introduces a methodology to enhance the shear-carrying capacity (SCC) of HS shear connectors through the incorporation of a concrete gradation in the slab. The study focuses on investigating the impact of the concrete gradation on headed stud shear connectors by dividing the concrete slab into two zones: Zone 1 and Zone 2. Six experimental push-out tests were conducted to evaluate the effectiveness of the concrete gradation concept on the stud's SCC. Subsequently, finite-element analysis (FEA) was performed using software to analyze the shear connector's ductility and failure mode. The parametric study considered size, shape, and concrete grade as the parameters for Zone 1. The numerical study results aligned with the experimental findings. Comparisons between graded and standard slabs showcased that a higher concrete grade in Zone 1 yielded superior results compared with normal standard slabs. The parametric study identified that the model combining M50+M25, M50+M30, and M40+M25 concrete grades exhibited better results, with an average percentage increase of 12.29%, 10.37%, and 4.49%, respectively, in the SCC of HS shear connectors. Additionally, adopting a cylindrical configuration for Zone 1 demonstrated enhanced stress distribution and increased SCC compared with a square shape for Zone 1. The parametric study further revealed a positive correlation between an increase in the dimensions of Zone 1 and increase in the SCC of the headed stud shear connector. Finally, two equations were proposed for evaluating the shear-carrying capacity of the headed stud embedded in graded concrete slab based on the dimensions of the Zone 1 region of the graded slab.