Abstract This study evaluates seven flat slabs made with reinforced concrete. There are three reference slabs, one of them doesn’t present any shear reinforcement. Four slabs have a new model of shear reinforcement of stud type, internally anchored to the flexural reinforcements. That reinforcement has an additional element, called on this study by the name: anti-cracking pins. The main objective of the research is to find the ideal spacing between these pins to achieve a failure mode and a failure load similar to the reference slabs that have conventional studs. For that, are evaluated: vertical displacements, rotation, shear reinforcement deformation, load capacity and failure mode. The slabs with the new stud have a load gain of 40% to 106% compared to the slab without studs LRef. The slab L-5-13 presented a load and a failure mode similar to the slab of reference, LRef-AC.

Resumo Esse estudo avalia sete lajes lisas de concreto armado. São três lajes de referência, dessas uma não apresenta armadura de cisalhamento, e quatro com uma novo modelo de armadura de cisalhamento do tipo stud, ancorado internamente às armaduras de flexão. Essa armadura possui um elemento adicional, denominado nessa pesquisa de pinos anti-fissuração. O objetivo principal da pesquisa é encontrar o espaçamento ideal entre esses pinos para atingir um modo e carga de ruptura semelhante às lajes de referência com studs convencionais. Para tanto são avaliados deslocamentos verticais, rotação, deformação das armaduras de cisalhamento, capacidade de carga e modo de ruptura. As lajes com o novo stud apresentam ganho de carga de 40% a 106% com relação à laje sem studs LRef. A laje L-5-13 apresentou carga e modo de ruptura similar à sua laje de referência LRef-AC.

Abstract Punching shear is a possible type of failure that occurs in reinforced concrete flat slabs, which can develop with an ultimate load below flexural capacity. Several researchers have studied the punching resistance of flat slabs over recent years. Although they have made great advances, there are codes that show different approaches to a singular design. Some codes show that there exist contradictions, even in the simplest situations, such as concentric loads. Most codes prescribe empirical expressions based in a theoretical model to analyze punching strength, but for flat slabs with holes around the column and shear reinforcement there are divergences between codes, justifying research in this area. This paper presents an experimental analysis of nine square reinforced concrete flat slabs under concentric loading (width: 1800 mm; thickness: 130 mm). The main variables used in the tests were: a) two square openings (150 mm) adjacent to the smallest side of the column and b) the use of shear reinforcement containing 3 layers, with 6 or 8 elements in each layer and radially distributed around the column. The research concludes that openings adjacent to the column affect punching shear strength, while the correct use of the shear reinforcement can minimize and even compensate this loss.