Static, fatigue and creep performance of blind-bolted connectors in shear experiments on steel-FRP joints

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.