Therefore, it is assumed that the load-carrying capacity can be estimated according to ultimate crack depth (directly measuring concrete’s compressive zone height). At the ultimate stage of crack propagation, the load-carrying capacity of the element is achieved. A different approach is proposed in this paper, that is, a crack model for direct calculation of flexural crack parameters which neglect the crack spacing. The researchers working on cracking phenomena of FRP-strengthened structures are trying to correct the empirical formulas to calculate crack spacing given by the design norms. In accordance with design provisions, the cracks in concrete open when a limiting tensile strain of concrete is reached therefore, the crack width can be calculated by multiplying the mean values of a difference between tensile reinforcement and concrete strains with crack spacing. There is a large quantity of researches made on the behaviour of the joint of concrete and FRP material, and the bond stiffness-reduction techniques are proposed, but none of the researches analysed by the authors was applied for prediction of concrete crack propagation. However, the effectiveness of strengthening can be compromised by loss of composite action, which can be delayed by using the additional anchorage. Strength properties could be used even more efficiently and economically by prestressing the FRP material. Anticorrosion properties are particularly relevant in aggressive environments, for example, bridge structures.
One of the most advantageous material types for strengthening is fibre-reinforced polymers (FRP) due to their corrosion resistance and high strength to low weight ratio. Retrofitting of existing structures is one of the main challenges for civil engineers today. The proposed analytical crack model can be used for more precise predictions of flexural crack propagation and load-carrying capacity. An experimental program is presented to verify the accuracy of the proposed model, taking into account anchorage and initial strain effects. At the ultimate stage of crack propagation, the load-carrying capacity of the element is achieved therefore, it is assumed that the load-carrying capacity can be estimated according to the ultimate crack depth (directly measuring concrete’s compressive zone height).
Contrary to the design norms, a crack model presented in this paper is based on fracture mechanics of solids and is applied for direct calculation of flexural crack parameters. Most studies on cracking phenomena of FRP-strengthened RC structures are directed to empirical corrections of crack-spacing formula given by design norms. The present study focuses on a prediction of crack width and load-carrying capacity of flexural reinforced concrete (RC) elements strengthened with fibre-reinforced polymer (FRP) reinforcements.
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