Estudo experimental do cisalhamento em vigas de concreto armado

Abstract

The dimensioning of reinforced concrete structures is of paramount importance for the field of civil engineering, since this is the material most commonly used in structural parts. The practical study of the possible ways of breaking a beam, due to shear stress, is intended to approximate theory and practice. Therefore, the main objective of this work is to study experimentally the influence of shear armature rate and shear span, on the final behavior and in service of reinforced concrete beams, evaluating mainly three aspects: vertical displacements, development of cracks and load and rupture mode. Finally, the experimental results were compared with those expected according to the calculation equations of norm NBR 6118: 2014. To achieve this goal, 8 beams with shear armature rates ranging from 0 to 0.82% and shear spans of 10 and 14 cm. The concreting and all the tests were performed at the Building Materials Laboratory of the IFG. The test consists of the application of two equidistant concentrated forces, with increasing gradient loading under constant velocity. During the tests load levels were defined that allowed the monitoring of the vertical displacements and the development of cracks. After the analysis of the results, it was concluded that the shear span and the a / d ratio have a significant influence on the actual behavior of the beams and that the increase of the shear span causes greater vertical displacements in the central region of the part and the higher the value , the earlier the first cracks appear. The reduction of the shear span gave a resistance gain of up to 40.2% to the parts and the decrease in the a / d ratio gave an increase in the rupture load of 14%. The parts with the highest transverse reinforcement rates showed the smallest displacements and the higher the transverse reinforcement rate, the greater the amount of visual shear cracks that the part presents before the rupture. As for the bursting loads, it is verified that the resistance gain, with the increase of the transverse reinforcement, reached 12%. It is possible to notice that the stirrups have little added in the resistance of the prototypes, unlike the shear span and relation a / d, that have a greater relevance in this point. Comparing the experimental result with the theoretical, it is verified that most of the prototypes presented the mode of rupture predicted by the equations, but with a load well above the calculated. The calculation model I was shown, with due reservations, closer to reality. In general, the prototypes showed behavior considerably different from that predicted by the equations of calculation of the norm, especially in relation to the load of rupture. However, this is mainly due to the fact that the prototypes have atypical dimensions, where the arc effect is present and quite relevant. The arc effect depends mainly on the a / d ratio, and when relevant gives the beam an increase in shear strength, but this factor is not predicted in the equations of NBR 6118, which suggests that the standard does not take it into account , justifying the differences between theoretical and experimental results.