Cisalhamento em vigas de concreto armado com armadura transversal interna contínua

Abstract

Reinforced concrete elements can suffer high bending and shear forces, either due to high loads, type of construction or architectural limitation, thus requiring a high longitudinal and transverse reinforcement rate, which can lead to conflicts between the two reinforcements, resulting in reduced productivity during the reinforcement work of the element. As a way to solve this reinforcement conflict, some researchers applied to reinforced concrete elements internal shear reinforcement, in other words, these reinforcements are positioned between the bending reinforcement bars, thus eliminating the conflict between the transverse and longitudinal bars and aiding the productivity of the reinforcement work, as this type of elements could be prefabricated and positioned as designed. However there are no normative standards that indicate the use of internal stirrups. Studies conducted on the subject indicated that the internal stirrups need an auxiliary device, as recommended by NBR 6118 (2014), which would help in the anchorage and allow the transfer of shear forces to the concrete without the delamination effect. Currently, few studies evaluate the performance of the transverse reinforcement with inclinations between 45º and 90º, where inclined stirrups provide better ductility and reduced stresses on compression struts. Therefore, this research presents a type of internal transverse reinforcement, tested in an experimental program and compared with closed-loop stirrups. The experimental program was carried out with a total of 5 beams of reinforced concrete, one as a reference with closed-loop stirrups, and the other 4 with internal stirrups; the main variables were: the inclination of the internal transverse reinforcement at 60º and 90º; and the number of legs of internal transverse reinforcement, keeping the same transverse reinforcement ratio. As results, this paper presents graphs of displacements, bending and shear reinforcement and concrete deformations, cracking maps and failure surfaces, and the last loads observed in the tests were compared with the theoretical loads estimated by different normative recommendations. As conclusions, it was observed that the internal stirrups have great potential in their use, as they present greater ductility and resistance compared to the closed-loop stirrup currently used. The results of inclined internal stirrups showed an increase of up to 14% when compared to the reference beam.