Due to the low weight and excellent durability of composite materials, Fibre Reinforced Polymer (FRP) decks mounted on steel superstructures are becoming increasingly common in engineering practice. Bolted joints are generally used to facilitate connections between an FRP deck and steel girders in road bridges. The connections are subjected to both high magnitude static forces as well as fatigue loading due to overpassing vehicles. With ever increasing traffic on both road and railway bridges, fatigue performance is of critical concern. Bolted FRP joints have been extensively researched in the past under static loading, but less is known about the fatigue and creep behaviour of such joints. Furthermore, little research exists on non-pultruded FRP profiles connected using bolted connections. Therefore, the objective of this research is to investigate connectors’ feasibility by means of static, fatigue and creep experiments on four different types of bolted joints comprising mechanical connectors and injection techniques. The study focuses on application in vacuum infused GFRP panels with integrated webs made of multi-directional laminates) connected to steel bridge superstructures. In addition, experimental results are used to validate Finite Element Analyses (FEA). Based on the obtained results, the novel injected steel-reinforced resin (iSRR) connector shows promising potential in hybrid steel-FRP bridges where good fatigue endurance of the connection, are required.

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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.

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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.

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The main challenge for realizing competitive hybrid steel-FRP structures, such as bridges, carparks, is to make the steel and FRP components work together. In this study shear resistance, stiffness and ductility of three types of demountable bolted shear connectors are examined. Two blind-bolted M20 shear connectors and a novel, injected steel-reinforced resin (SRR) connection are selected to perform push-out experiments in web-core FRP decks. Failure modes of excessive bearing in FRP and bolt shear failure for blind-bolted and injected connectors, respectively, are identified. Nonlinear, highly detailed finite element (FE) models were also built and validated by results of the push-out tests to provide insights to the load-transfer mechanism. Analysis of internal forces and deformation through FE results reveals that blind bolted shear connectors provide high shear resistance and slip capacity thanks to the shear sleeves and catenary effects. The injected SRR connector shows distinct and centric load transfer owing to gapless design.

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Pin-bearing is a favourable failure mode in bolted glass fiber reinforced polymer (GFRP) joints because itoffers quasi-ductile behaviour due to complex failure mechanism involving: matrix cracking, fibre fractureand delamination. Such complexity brings the challenge in prediction of failure through FE modelling withstate of the art studies mostly being limited to very small joint geometries due to large computational costsof very detailed 3D models. Aim of this study is to show the applicability of an efficient modelling approachfor analysing complex model geometries in structural engineering applications and to understand its failuremodes. In the applied modelling technique, the laminate is represented by a series of continuum shellelements, while cohesive interaction property with bilinear constitutive law is defined between the sublaminates to capture delamination failure. The FE model built in Abaqus/Explicit is calibrated to loaddisplacement curves of double-lap single-bolted joints. A calibration methodology is developed incorporatingthe effect of the number of elements in thickness direction on the bearing response of the laminate. Residualbearing strength of the elements subjected to matrix compression, which is not captured by the inbuiltdamage model, is achieved by the modification of maximum damage index. The modelling approach provedto be computationally efficient, while capturing all relevant failure modes, and replicating damage patternsof the specimens, therefore it can be recommended for larger scale FE models.@en

Demountable connectors have been rarely applied in steel-FRP hybrid structures due to the lack of research, which could prove their reliable structural performance. In typical applications, e.g. in multi-girder hybrid decks, the connectors are not only subjected to longitudinal shear forces, but also to substantial tensile forces originated from the uneven load distribution between the girders. Therefore, the aim of this study is to investigate the feasibility of three types of bolted connectors in steel-FRP hybrid structures by examining their shear and tensile resistance. To that end, push-out and pull-out tests were conducted to determine respectively, the shear and tensile strengths of the connectors. The suitability of the connectors in typical multi-girder hybrid steel-FRP deck applications is concluded from the test results.

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