Due to constantly increasing traffic loads and ageing infrastructure, innovative materials for implementation in renovation and new bridge construction projects are gaining attention. One such innovation is hybrid structures consisting of Glass Fibre-Reinforced Polymer (GFRP) composite decks connected to a steel girder(s) superstructure. By combining the stiffness provided by steel members with the superior fatigue endurance and strength to weight ratio of FRP, the properties of both materials can be efficiently exploited. The main restriction to the implementation of hybrid steel-FRP structures lies in the lack of knowledge and efficient technical solutions for the connection between the two materials. Adhesively bonded and grouted connections have been identified as possible connection systems, whereas limited research has been performed on bolted connections. To address this research gap, this paper discusses an experimental investigation into the performance of two types of slip-resistant bolted connectors, namely conventional resin injected bolts and a novel connector system developed at TU Delft comprising of a bolted connector injected with steel reinforced resin (iSRR). Connectors’ performance is evaluated by means of long-term (sustained and cyclic) and short-term experiments with shear load. A single-lap shear joint configuration is used to compare performance of the two connector types. A vacuum infused GFRP multi-directional laminated plate, 20 mm thick, is connected to steel plates by means of M20 bolts. Results indicate comparable stiffness, resistance and ductility of the two connector types in short-term experiments. Superior fatigue performance of iSRR connector is found with 100 times more fully reversed load cycles that are needed to reach the same failure criterion as the conventional injected bolts.

As traffic loads are ever increasing and bridge infrastructure is ageing, existing materials and connection methods used in renovation and new construction projects are reaching their limits. New materials, such as Fibre-Reinforced Polymer (FRP) in the form of hollow decks can be a competitive solution due to good resistance to fatigue and corrosion. By combining the stiffness provided by steel main and secondary girders with lightweight FRP decks, the properties of both materials can be efficiently utilised. However, the main restriction to the implementation of hybrid steel-FRP structures lies in a lack of knowledge regarding the level of interaction as well as efficient and durable connection solutions of FRP decks and steel girders. Adhesively bonded and grouted connections have been identified as possible connection systems, whereas limited research has been performed on bolted connections. This paper focuses on blind-bolted shear connectors. Connector performance is evaluated experimentally by means of short-term (static) experiments to determine shear resistance and long-term experiments with sustained (creep) and cyclic (fatigue) loading. A vacuum infused GFRP multi-directional laminated plate, 20 mm thick, is connected to steel plates by means of M20 blind-bolts. Static resistance, fatigue and creep behaviour of blind-bolted connectors, as a bearing type, are compared to results of a parallel experimental campaign conducted on slip-resistant injected connectors. A comparable static resistance and ductility is found. However, fatigue endurance is much lower compared to slip-resistant connectors. Therefore, due to low fatigue endurance, low initial stiffness and initial slip, the use of blind-bolted connectors is limited to applications where hybrid interaction and fatigue endurance is not required.