Conventional vs. reinforced resin injected connectors’ behaviour in static, fatigue and creep experiments on slip-resistant steel-FRP joints

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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.