Punching shear failure behaviors of unbonded prestressed slab-column connections: Numerical investigation and code comparisons

Reinforced concrete slab-column (RCS-C) structures are a popular choice due to their flexible layout and space-saving characteristics. However, due to the absence of beams, slab-column structures are prone to developing cracks or noticeable deformation over long-term use. Therefore, the unbonded prestressed slab-column (UBPS-C) structure has become a prevalent solution because it can effectively address the aforementioned issues and is convenient to construct. The connection between the slab and column is the most critical area in slab-column structures. However, construction-stage stacking or service-life overloading may induce punching shear failure in these connections, posing significant risks to both human safety and property integrity. In this study, numerical models of RCS-C connections and UBPS-C connections were developed to investigate their structural behavior and failure mechanisms under punching shear. There is no transverse reinforcement or shear reinforcement in the floor slab. Comparative analysis reveals distinct failure patterns that RCS-C connections demonstrate conventional conical punching failure, whereas UBPS-C connections exhibit a unique peripheral shear failure characterized by circular damage propagation along the outer perimeter. The prestressing tendons are shown to significantly improve both load-carrying capacity and structural ductility. Furthermore, an evaluation of different design codes, including GB 50010-2010 (China), ACI 318-19 (America), CSA A23.3-04 (Canada), Eurocode 2 (EN 1992-1-1) (Europe), and JSCE 15-2007 (Japan), for punching shear resistance prediction, was conducted in the present study. Subsequently, the corresponding suggestions were proposed. GB 50010-2010 is the most conservative, thereby suggesting that the factors should be increased or the effect of reinforcement should be introduced. For ACI 318-19 and CSA A23.3-04 , it is recommended to reduce the upper limit of the prestressing terms to improve performance under high prestressing conditions. The increase in the contribution of prestressing in Eurocode 2 could be considered to obtain superior precision for prestressed slab-column connections. JSCE 15-2007 has been shown to overestimate the positive effects of concrete and reinforcement.