Steel-reinforced resin for bolted shear connectors: Confined behaviour under quasi-static cyclic loading

Injections bolts were initially conceptualized to repair riveted connections in bridges with long service lifetime and now they are widely used in steel and composite structures. Injecting steel-reinforced epoxy resin in bolted connections with oversized holes is a novel approach to enable fast and easy assembly of composite structures while limiting slip between the components. The performance of these bolted shear connectors is mainly dependent on the injected material. In this paper, short-term mechanical properties of an epoxy-based resin mixed with steel shots (steel-reinforced resin) are evaluated to consider it for bolted shear connectors. Uniaxial static tests allowed to compare the stiffness and ductility of resin and steel-reinforced resin and to define a hardening law, while multiaxial tests were conducted under quasi-static cyclic loading in order to characterize the material behaviour under confined conditions. Steel-reinforced resin specimens showed a stiffness under confined conditions 2.6 times higher compared to the bare resin specimens. This increase of stiffness is fundamental to achieve slip resistant behaviour when resin-injected shear connectors are used in significantly oversized holes. The linear Drucker-Prager plastic model was used to define the material behaviour. The good agreement observed indicates that future investigations on numerical and experimental performance of bolted shear connectors can be implemented with the parameters proposed in this paper.