Effect of tension and compression flexural reinforcement on punching shear strength of reinforced concrete flat slab

Abstract

To better understand how a flat slab responds to a punching effect with varying effective parameters, an experimental and numerical program was carried out in this study. The studied parameters included the flexural reinforcement (RFT) ratios, whether in tension or in compression, the concrete compressive strength (fcu) and using of stirrups. For this purpose, eighteen R.C flat slab were casted and tested in the R.C laboratory at Cairo University. All slabs had the same dimensions of (1100 ×1100) mm and the slabs thickness is 120 mm with a square column dimension equal to (150 ×150) mm at the center of slabs. The ratios of flexural RFT in tension and compression sides were (1.27, 1.76, and 2.25) % and (0.48, 0.75 and 1.09) % respectively. The tested slabs were casted with fcu (35 and 45) MPa. All the previous mentioned parameters were investigated in the presence and absence of stirrups. First cracking load, ultimate load capacity, crack pattern, load-deflection relationship, stiffness, energy absorption and RFT strain were analyzed and discussed to show the parameters’ effects on all studied slabs. The results revealed that flexural tension RFT had a noticeable effect on the punching shear behavior compared to the compression one; which had a slight effect. Non-linear finite element 3-D models were verified with the experimental results and parametric study was conducted. Finally, the experimental results were compared and verified against different building design codes of practice (ACI 318, Eurocode 2 and ECP 203). The used codes were capable of estimating the shear capacity; but with conservative values. Eurocode 2 gave better prediction as it takes the flexural tension RFT into consideration. New equations were proposed to predict the punching shear strength considering flexural tension RFT ratio in case of presence and absence of stirrups.