Performance of GFRP reinforcement as friction shear connectors in concrete composite elements

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Aljada, Basel
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Composite reinforced concrete (RC) beams composed of cast-in-situ slabs and pre-cast beams have been commonly used due to their economic advantage over ordinary beams. Maintaining integrity between the beam and slab components is essential to ensure monolithic behaviour. This integrity can be maintained only if the friction shear along the joint interface resulted from the gravity load is resisted. The characteristics of the reinforcement crossing the joint interface, concrete strength, and shear plane condition are some of the main factors controlling the integrity of composite elements. Given their lighter structures, composite beams are widely utilized in structures that require long spans, such as bridges and parking structures. However, these RC structures are usually susceptible to severe environmental conditions, especially in cold regions, that will accelerate the steel corrosion process. Substituting the conventional steel with a non-corrodible material such as glass fibre-reinforced polymer (GFRP) has proven to be a viable alternative. In this study, a pioneer investigation was conducted to assess the feasibility of using GFRP as shear connectors in concrete composite elements. The study involved constructing and testing 26 large-scale push-off specimens under monotonic axial load. Twenty-one out of these specimens were reinforced with GFRP connectors, whereas the remaining were reinforced with steel connectors serving as control specimens. Each specimen consisted of two L-shaped blocks that were cast either monolithically or at different times to simulate the cold-joint condition. The specimens were 1,050 mm long, 600 mm wide, and 300 mm deep. The main tested parameters were reinforcement type (GFRP or steel), ratio (0.17-0.48%), and shape (closed stirrups and Z-shaped bars), concrete strength (35 and 70 MPa) and shear plane condition (cold-jointed not roughened, cold-joint roughened, and monolithic). The test results demonstrated that GFRP can be used as shear connectors and the overall, behaviour is dependant on the reinforcement ratio and concrete strength. Increasing the reinforcement ratio and concrete strength increased the load carrying capacity significantly. Moreover, the results showed that closed stirrups provided better clamping stresses than the Z-shaped bars. Furthermore, monolithic shear plane condition resulted in having much higher capacities over the cold-jointed counterpart specimens.
Cold joint, Composite elements, Friction shear, Glass fiber-reinforced polymers (GFRP), push-off, Shear connectord, Monolithic