Abstract
abstract: This paper assesses the influence of slab continuity on the punching resistance of a realistically proportioned flat slab floor plate without shear reinforcement. The edge column punching resistance of a symmetric flat slab extending bays in each direction was assessed by means of NLFEA with TNO DIANA, MC2010 levels II, III, IV, Eurocode 2 and NBR 6118. Both Eurocode 2 and NBR 6118 are seen to give similar predictions for punching resistance, while MC2010, which is based on the Critical Shear Crack Theory and depends on how rotations are calculated and FE modelling assumptions, varies significantly with its levels of approximation with Level IV agreeing reasonably well with predictions from NLFEA. Direction for the critical rotations is shown to vary and can also be influenced by the reinforcement over the span. For EC2, NBR 6118 and MC2010 LoA II and III punching shear design are independent of span, unlike the results obtained with MC2010 LoA IV.
Highlights
Flat slabs are two way spanning slab directly supported by columns
This paper addresses some of the theoretical issues regarding the punching shear resistance of flat slabs, while giving and comparing the amount of punching shear reinforcement required based on predictions of Brazilian’s NBR 6118 [17], Eurocode 2 [18], and MC2010
This paper investigated the impact of slab continuity through modelling assumptions, critical directions of rotations and code comparison on the punching resistance of an edge column from realistically proportioned flat slab floor plates
Summary
Flat slabs are two way spanning slab directly supported by columns. Their thickness is typically governed by deflection control or punching shear resistance. Fib [2] mentions that based on experimental results developed by Sherif [8] it can be concluded that the punching shear strength of an interior slab-column connection in a realistic slab is almost the same for a single column test specimen Issues like this one led fib [2] to remark that, for design purposes, it is still not recommended to rely on compressive membrane action. They can give very conservative estimates of the shear resistance of slabs designed in accordance to UK practice using the equivalent frame method, where moments are typically redistributed downwards by 20% over columns Both tests and the CSCT suggest that this inward movement of the line of radial contraflexure should lead to an increase in shear resistance. It aims to discuss a few modelling assumptions adopted which are relevant on the interpretation of the results, such as the consideration of elastic columns in the numerical analyses required by MC2010 LoA III and IV in order to calculate the punching shear
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