Análise experimental do comportamento estrutural em protótipos de lajes lisas em concreto armado submetidas à punção

Abstract

The design of reinforced concrete flat slabs presents punching shear as a critical point, given that shear stresses concentrate around the columns, potentially leading to slab rupture. Currently, despite numerous research efforts in the field, there is still no definitive method to solve this problem. Standards recommend the use of reinforcements such as vertical stirrups or connectors (studs) to resist punching shear, with a preference for the latter. However, punching failure can occur outside the shear reinforcement zone when punching reinforcement does not adequately extend into the slab. To mitigate this deficiency, fibers can be used in the concrete composition as they help control crack widths, transforming brittle failure into ductile failure. This experimental study investigated the structural behavior of reinforced concrete flat slabs during punching shear tests. Six square slabs measuring 1200 x 1200 mm with 100 mm thickness were tested to failure, with different percentages of steel fibers (0%, 0.50%, and 0.75%) and stud-type shear reinforcements. The objective was to analyze not only the strength of the slabs but also the crack pattern and vertical displacement during the test. The results indicated that the addition of steel fibers increased the ultimate load of the slabs compared to the reference slabs, with a fiber content of 0.50% showing the best performance. On the other hand, the use of shear reinforcements resulted in a reduction in the ultimate strength of the slabs, except in the case of slabs with 0.75% fibers. The introduction of shear reinforcement caused vertical displacements to abruptly increase in the slab without fibers, while providing more uniform displacements in the slabs containing 0.50% and 0.75% steel fibers.