Waffle slabs. Punching shear reinforcement

If punching shear is required, a detail (as shown in the figure) should be included in the drawings of the structure.

c: Cover

a > 10ø or 15cm


The spacing of the reinforcement will depend on the analysis carried out by the program.

We propose another solution in case the concrete requires transverse punching shear reinforcement (if the resistance capacity of the concrete is not overcome). This solution consists in introducing, either before the analysis or after it, once it has been seen that punching shear is required, two beams or cross-beams, initially flat beams, placed orthogonally over the column. These beams can have a width of 30cm, regardless of the size of the column and a length equal to the length of the drop panel (1/6 of the span at either side of the column). In the case of a waffle slab, the longitudinal reinforcement of the cross-beam serves as assembly reinforcement of the drop panel. The same recommendations apply for flat slabs.

Once these beams have been introduced, and due to the way in which the structure is discretised, the shear force is concentrated on them and the rest of the infilled area is relieved of this load. Hence the program reinforces the beams for the corresponding shear force.

Attention: Introduction of the cross-beams does not prevent the concrete from failing due to oblique compression because of shear. If the concrete section fails without introducing the cross-beams, it will continue to do so having introduced them, unless these are introduced as dropped beams, which could solve the problem of the concrete failure due to overcoming its resistance capacity.

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