SHEAR STRENGTH PREDICTIONS OF LONGITUDINALLY REINFORCED CONCRETE BEAMS

Abstract

The flexural behavior of reinforced concrete (RC) members has been well understood such that their flexural strengths are predicted with reasonable accuracy over a wide range of cases. By contrast, it has been difficult to predict the shear strengths of RC members accurately due to the uncertainties in the shear transfer mechanism, especially after cracks are initiated. Many current design codes follow the `V,+VS' philosophy for shear design in which the web reinforcement is designed using fixed-angle or variable-angle truss models to resist a shear force of `Vs' obtained after accounting for the shear resisted by concrete, V. The `Vc+VS'approach gives reasonable lower-bound predictions for the shear strength of slender R.0 beams though this approach becomes overly conservative as far as shear strength predictions of relatively stocky or deep beams is concerned. In this investigation, an attempt has been made to use strut-and-tie models for analytical predictions of the ultimate shear capacities of deep beams and the proposed procedure has been validated by comparing with experimental results reported in the literature. The proposed procedure has been seen to yield results which are in close agreement with experimental results for beams with aid values typically less than 3.0, For aid values greater than 3.0 the shear strength predictions using the strut-and-tie models were found to be more conservative compared to the predictions of the `V,+VS' approach. The results of a parametric study carried out using the finite element package ATENA 3.1.0 to investigate the influence of aid, amount of tension reinforcement and compressive strength of concrete on the ultimate shear capacity of singly reinforced simply supported R.C. beams are also reported.