Abstract
Failure of flat slabs usually occurs by punching shear mode. Current structural codes provide an experience-based design provision for punching shear strength which is often associated with high bias and variance. This paper investigates the effect of adding a horizontal reinforcement mesh at the top of the slab-column connection zone on punching the shear strength of flat slabs. A new equation considering the effect of adding this mesh was proposed to determine the punching shear strength. The proposed equation is based on the Critical Shear Crack Theory combined with the analysis of results extracted from previous experimental and theoretical studies. Moreover, the equation of load-rotation curves for different steel ratios together with the failure criterion curves were evaluated to get the design points. The investigated parameters were the slab thicknesses and dimensions, concrete strengths, size of the supporting column, and steel ratios. The model was validated using a new set of specimens and the results were also compared with the predictions of different international design codes (ACI318, BS8110, AS3600, and Eurocode 2). Statistical analysis provides that the proposed equation can predict the punching shear strength with a level of high accuracy (Mean Square Error =2.5%, Standard Deviation =0.104, Mean=1.0) and over a wide range of reinforcement ratios and compressive strengths of concrete. Most of the predictions were conservative with an underestimation rate of 12%. Doi: 10.28991/CEJ-2022-08-01-013 Full Text: PDF
Highlights
Flat slabs are reinforced concrete one-way and two-ways slabs in which beams or girders are not provided, and their loads are directly transformed to the supporting columns
The findings revealed that the reinforcement ratio has a greater effect on punching shear strength as compared with normal-weight concrete
Using Critical Shear Crack Theory, the load-rotation equation curves for different steel ratios together with the failure criterion curve were evaluated to get the design point that represents the intersection of the two curves are used in formulating the proposed model
Summary
Flat slabs are reinforced concrete one-way and two-ways slabs in which beams or girders are not provided, and their loads are directly transformed to the supporting columns. A new model for both normal and high strength concrete was proposed by Annash et al [14] This model considered the effect of critical section position, concrete compressive strength, slab effective depth, reinforcement ratio, and dimensions of the column and its shape. Their model proved to give closer predictions of the as compared with different codes. The contribution of the proposed horizontal mesh of reinforcement at the top of the slab-column connection zone on punching shear strength was analyzed in detail by comparing the experimental results extracted from different published work with the current structural design codes. The proposed formula may form the base for predicting the punching shear capacity of such flat slabs
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