Influência dos ângulos de biela e tirante no volume de armadura transversal de vigas

Abstract

The design equations for reinforced concrete structures presented by the codes aim to simplify the calculation process for the designers taking into account the safety conditions. Requiring reducing costs in the current constructions, projectists seek for techniques that reduce the consumption of materials, mostly using optimized models. The Brazilian code NBR 6118 (ABNT, 2014) allows the designer to choose between two models to determine the transverse reinforcement of concrete beams, based on the truss model proposed by Ritter and Morsch at the beginning of the 20th century. In Model I the angle of inclination of the compression struts is fixed at 45º and the shear force resisted by the concrete is constant, while in model II the angle value of the compression strut can be varied in the range between 30º and 45º, and the shear force resisted by the concrete is variable according to the acting shear force. In both models the ties can be inclined between 45º and 90º. In this work a numerical analysis of the volume of transverse reinforcement in simple beams with distributed uniform load is carried out, having as variables the concrete compressive strength, the intensity of the acting shear force and the relation between the span and the effective height of the cross section, determining the struts and tie angles that lead to a lower consumption of transverse reinforcement.