Behaviour of GFRP-RC slab-column edge connections with openings

Abstract

Flat plate Reinforced Concrete (RC) slab-column connections are widely used due to their structural efficiency and architectural advantages. However, these systems are vulnerable to brittle punching shear failure, particularly in edge connections subjected to combined shear and unbalanced moment. The presence of slab openings near the column further disrupts load transfer, reduces the effective shear-resisting area and increases stress concentrations. In aggressive environments, durability concerns associated with steel reinforcement have prompted the use of Glass Fibre-Reinforced Polymer (GFRP) as a corrosion-resistant alternative. Although previous studies have examined GFRP-RC slab-column connections, limited information is available on their behaviour in the presence of openings and shear reinforcement. This study experimentally investigated the behaviour of full-scale slab-column edge connections reinforced with GFRP bars. Eleven specimens were constructed and tested to failure under combined vertical shear and unbalanced moment while maintaining a constant moment-to-shear ratio representative of practical conditions. The investigated parameters included the opening location, size and distance from the column face and the use of GFRP headed-end bars and shear studs. In addition, an analytical investigation was conducted to assess the accuracy of current North American code provisions and to explore the effective flexural width of the slab at edge connections. Furthermore, Finite element modelling was carried out to broaden the study and extend the investigated parameters. The results showed that all specimens failed in punching shear. The presence of openings significantly altered the load-transfer mechanism and cracking behaviour. Openings located at the column front face resulted in the most severe reduction in punching shear capacity, whereas openings located further away had a less pronounced effect. Increasing the distance between the opening and the column improved the structural response, with minimal influence observed at larger distances. The use of shear studs enhanced punching shear capacity and improved post-peak deformability. The findings demonstrate that GFRP-RC slab-column edge connections can achieve reliable performance under combined loading conditions. However, the presence and location of openings must be carefully considered in design. In addition, current design provisions do not adequately capture the influence of openings and shear reinforcement on punching shear capacity.