Improved empirical model for the strut efficiency factor and the stiffness degradation coefficient for the strength and the deflection prediction of FRP RC deep beams

Abstract

In this paper, an improved empirical model for the strut efficiency factor βsis proposed in the softened strut and tie model to predict the ultimate load of the concrete deep beams longitudinally reinforced with fiber-reinforced polymer (FRP) bars that failed in shear. The proposed model accounts for the influence of the shear span to depth ratio a/d, the concrete compressive strength fc', the area of the FRP reinforcement Af, the diagonal strut angle θ and the width of the loading plate lb. In addition, an improved empirical model for the stiffness degradation coefficient kf, accounting for the influence of the overall depth of the beam h and the strut angle θ is proposed to predict the corresponding ultimate deflection. The proposed models are validated by accounting for the maximum range of the parameters involved in the database. The engineering significance of the various parameters involved in the proposed models are illustrated by carrying out parametric study. In addition, the proposed model is assessed with the other models for the strength and the deflection prediction using the data base used in this study. The prediction shows that the proposed models can accurately predict the ultimate load and the mid span deflection of FRP bar reinforced concrete deep beams for the various range of values of the parameters involved.