Abstract
ABSTRACT This paper is related to the punching shear in prestressed slabs with unbonded tendons for interior columns calculated by the codes ABNT NBR 6118:2007, ABNT NBR 6118:2014, EN 1992-1-1:2004 e ACI 318-11. To calculate the punching shear resistance the formulations of the NBR 6118:07, effective until April/2014, did not consider the compression of the concrete in the plane of the slab, due to prestressing. Just the inclined components of some tendons were considered for total load applied relief, but this fact did not generate a significant difference, compared to reinforced concrete, because the inclination angle is very close to zero. The American and European provisions consider a portion related to the compression of the concrete in the planeof the slab. Differences in the results obtained by the four design codes will be exposed, showing that the EC2:04 and the NBR6118:14 achieved the best results.
Highlights
2.1.2 Internal column with symmetrical loading1.1 Justification and motivationThe motivation for this article is due to the fact that the Brazilian, European and American codes have different formulations for calculating the punching shear in prestressed slabs, generating different results from the same input data
The analyzes show that Eurocode is a standard that generates more economic results of punching shear reinforcement, especially for higher loads, followed by NBR 6118:2014 and NBR 6118:2007
For slabs with small overload, ACI 318-11 can generate an economic design, since the code can generate a result that dispenses the use of the punching shear reinforcement
Summary
The motivation for this article is due to the fact that the Brazilian, European and American codes have different formulations for calculating the punching shear in prestressed slabs, generating different results from the same input data. Formulations of the NBR 6118: 2007 standard that was in effect until April 2014, do not consider the concrete compression in the slab plane, due to prestressing. The American and European standards consider a portion related to concrete compression in the slab plane. In order to obtain less conservative results, ABNT revised the formulation to design punching shear in the new NBR 6118: 2014 by inserting a portion related to compression in the slab plane, due to prestressing as Eurocode 2 suggests. The results of this paper can show the influence of compressed concrete by the use of prestressing with greased tendons
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