French standard NF EN 1992-1-1 clearly defines the rules for dimensioning slabs with regard to punching. It also allows to verify shear at the interface between concrete’s cast at different times.
However, this standard doesn’t explicitly indicate how to verify the punching of precast slabs, contrary to French old standard BAEL which indicated a reduction factor of 2/3 whose origin remains unknown.
The first numerical work was carried out within the framework of the NC008 study: « Drafting of NF DTU standards for the design and implementation of precast concrete structural products ». This work allowed to present the first linear numerical calculations to the BNTRA EC2 commission (subject n° 50a). The conclusion of this work was an obtained reduction coefficient equal to 2/3, which is the same as the one previously mentioned in the BAEL. During the presentation of the results, the committee wished to have at its disposal additional nonlinear calculations integrating the influence of the joint.
In this context, the CERIB’s structure team, after having carried out the non-linear calculations meeting the requirements of the commission, presented during a second BNTRA EC2 session in July 2018, the results of this report as well as the associated proposals.
During this meeting, the BNTRA EC2 commission agreed to introduce these proposals in the next revision of French standard NF EN 1992-1-1 application guide, the FD P18-717 documentation booklet.
These proposals will allow precast French companies to rely on a normative text when a justification for the punching resistance of precast slabs is necessary.