MODEL OF SHEAR RESISTANCE OF CONCRETE ELEMENTS REINFORCED WITH FRP BARS

Abstract

Introduction. The problem of shear resistance of reinforced concrete elements without transverse reinforcement remains, as before, one of the most controversial in the theory of concrete structures. A new interest in the problem arose in connection with the use of polymer composite (FRP) bars as longitudinal reinforcement in concrete structures. The models of shear resistance included in the regulatory documents and formulated as proposals for elements reinforced with steel bars and FRP bars are considered. It is shown that the critical shear crack theory (CSCT) can be adopted as a basis for formulating a model of shear resistance of FRP-reinforced elements. However, its provisions cannot be applied directly without appropriate adjustments, in particular, regarding the determination of the width of the opening of a critical crack. Materials and methods. To determine the shear strength of self-stressed concrete elements reinforced with FRP bars, a modified model has been developed. This model, using an iterative procedure, makes it possible to determine a separate contribution to the total shear strength of each of its main components, taking into account the shape of the potential inclined crack, adopted in accordance with the provisions of the Critical Shear Crack Theory (CSCT), as well as the width of the opening of the inclined crack at the level of the longitudinal reinforcement, determined according to the law of "bond-slip" for FRP bars. Results. The reliability of the proposed modified shear resistance model is confirmed by comparing the calculation results with the results of our own experimental data, and with the results of research by various authors (database). Based on the results of a parametric study, a phenomenological shear resistance criterion for flexible elements reinforced with polymer composite bars was proposed, on the basis of which a simplified design model was developed that allows determining the shear resistance of concrete elements reinforced with FRP bars without the need to calculate all components of the shear force. Conclusions. The proposed model of shear resistance of flexible self-stressed elements reinforced with FRP bars reflects the physical essence of the shear phenomenon and is applicable to various cases and loading schemes.