Critical view on the level of maximum punching strength of flat slabs and column bases using database evaluations

The level of maximum punching strength is of major importance to design highly stressed slab-column connections and to choose the type of punching shear reinforcement. Since a couple of years, there is consensus that the maximum punching strength of shear-reinforced concrete slabs can be defined as a multiple of the reference punching strength without shear reinforcement. The upper bound of this load-increasing effect depends mainly on the anchorage and arrangement of shear reinforcement elements. Despite numerous research studies and database evaluations, there are ongoing discussions regarding the final effectiveness of stirrups and double headed studs installed in flat slabs and column bases. In this paper, a strictly filtered punching database is used to highlight the significant impact of underlying reference strength comparing the maximum load increase according to current Eurocode 2 and the draft for the next generation of Eurocode 2 (prEC2). Based on this unifying database, the origin of current discrepancies is discussed and a combination of constant lower bound coefficients with a refined formula as specified in prEC2 is proposed. Additionally, the effect of adapting current European Technical Approvals for double-headed studs and punching shear optimized lattice girders to prEC2 is shortly analyzed. A further database evaluation also allows for setting the basis for optimized detailing provisions regarding the maximum permissible diameter of shear reinforcement.

Automated summary

The study investigates the importance of maximum punching strength levels in designing highly stressed slab-column connections and selecting the type of punching shear reinforcement. By using a strictly filtered punching database, the impact of various factors on the load increase effect is analyzed, leading to recommendations for adjusting current European Technical Approvals.