Resistência ao cisalhamento de vigas “T” de concreto armado: verificação das longarinas da ponte sobre o rio Sororó

Abstract

The structural behavior of a T beam gives assessment of different contributions on shear strength between different parts of the same cross section, allowing to establish guidelines for the provision of shear and flexure reinforcement. To quantify the contribution of the flange and web of such section in the shear strength were experimentally investigated 10 reinforced concrete beams consisting of T section aiming to evaluate the recommendations of NBR, ACI and EC2 standards about T beams subjected to shear. One of the beams was the control beam to be compared with, the others were idealized with a variation on the size of the cross section of the flange, to increase the cross section concrete area. All of the beams had no stirrups and the longitudinal reinforcement was the same in all cases. The concrete compressive strength was 47 MPa. It is clearly observed that the cross section made great influence on the shear ultimate strength of the structural elements tested in the laboratory, despite the sudden collapse, it is understood that the development of critical shear cracks depends on how the longitudinal tension is distributed in accordance with shear. The rise of the ultimate strength in the beams with flanges was observed to a level near the double of the ultimate shear force presented by the beam , and more clearly in beams with hf=80 mm, in which the concrete contributions were able to modify the collapse of those specimens, due to the yield of the tensile reinforcement, and the gain of stiffness that was about 25% higher when compared to the rectangular beam in terms of displacements. Through the acquired results it was possible to estimate the ultimate shear strength gain of the beams of the bridge over the Sororó river of the Carajás railway, giving a gain of a rectangular beam strength multiplied by 1,93 in that case.