Punching shear reinforcement in crosswise arrangement – Effective or impermissible?
Stud rails used as punching shear reinforcement in flat slabs are arranged radially in Germany. A crosswise arrangement in the layout of the reinforcement elements, as it is common practice in North America for easier installation, is not permitted in
Germany. The areas in the corners of the cross joints remaining without shear rein-forcement decline the punching shear resistance compared to punching shear points with an all-over reinforcement arrangement.
The Filigran punching shear reinforcement consisting of welded three-dimensional reinforcement elements is used in semi-precast floor slabs along with lattice girders arranged in parallel to the same [1]. This arrangement ensures an ease of installation. However, not all inclined load-bearing struts of the punching shear reinforcement are directed ideally into the direction of the column.
The effectiveness of the Filigran punching shear reinforcement is enhanced by a crosswise arrangement with inclined reinforcement elements being directed towards the column. Such an orthogonal arrangement, in contrast to a radial arrangement, retains the ease of installation in respect of both the punching shear reinforcement and the upper bending tensile reinforcement. Larger areas without shear reinforcement are avoided by the installation of additional reinforcement elements next to the cross-shaped design (Fig. 1). Building component tests using this arrangement showed highest punching shear resistances [2]. The European Technical Assessment ETA-13/ 0521 [3] approves an enhanced punching shear reinforcement for this reinforcement arrangement by a factor of 2.1 in contrast to slabs without shear reinforcement. This easy-to-install version is particularly suitable when in-situ concrete is used.
