Punching of reinforced concrete flat slabs with holes and shear reinforcement

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.

Punching shear in concrete reinforced flat slabs with steel fibers and shear reinforcement

“…According to Trautwein (2011), a punching shear failure may lead to progressive collapse if the structure does not have enough load redistribution capacity. Several variables influence punching shear in flat slab design such as the use of high strength concrete, column geometry at the slab interface, slab depth and use of reinforcement to improve shear strength as shown in previous research done by Gomes and Regan (1999), Borges, Melo and Gomes (2013) and Silva et al (2017). According to Maghsoudi and Sharifi (2009), self-compacting concrete (SSC) improves the punching shear strength of slabs although they present less ductility then conventional concrete and a smoother failure surface thus decreasing the contribution of aggregate interlock.…”

Empirical Punching Shear Capacity Equation for Reinforced Concrete Two-way Slabs with Openings

“…Likewise, the capacity ratios calculated with the nonlinear punching circumference ratio equation proposed in Eq. (25), which is proposed within the scope of this study, are given in Table 7. It is seen that the proposed equation for circular openings, in which the suggested results in Table 7 are examined, does not give as successful results as for slabs with square openings.…”

“…It was stated that the results were in good agreement with the finite element analysis results. After a detailed literature review to determine the maximum punching bearing strength values of opening two-way reinforced concrete slabs within the scope of the study, Živković et al [5]; Pinto et al [6]; Augustin et al [7]; Lourenço et al [8]; Bompa and Onet [19]; Oukaili and Salman [20]; Durucan and Anil [21]; Ha et al [22]; Ilbegyan et al [23]; Abduljaleel et al [24]; Silva et al [25]; Balomenos et al [26]; Liberati et al [27]; Kormosova et al [28] have been found. After a comprehensive literature review, the limited number of studies listed above were found, examining the effects of openings on the maximum bearing capacity of two-way reinforced concrete slabs under punching loading.…”

Effect of Shape, Number, and Location of Openings on Punching Shear Capacity of Flat Slabs

“…ACI 318-19 [18] provisions were used to calculate the shear and flexural strengths of specimens. Shear strength provided by concrete is calculated using Equation (1).…”

“…Nowadays, flat slabs are widely used because of their simple reinforcement details, reduced building heights, rapid construction etc. A flat slab without beams is less rigid and open to larger vertical displacements than conventional slabs [1,2]. Flat slabs are prone to punching shear due to the accumulation of high shear stresses in the vicinity of slab-column junction [3,4].…”