Punching performance of flat slabs with openings accounting for the influence of moment transfer and shear reinforcement

The arrangement of openings adjacent or near to slab-column connections is very common practice in flat slab design due to a number of advantages for technical installations. Such location is however conflicting with the most critical region of the slab, where punching shear failures may develop and typically govern the design at ultimate limit state. This requires in many cases arranging shear reinforcement to enhance the performance of the connections both in terms of resistance and deformation capacity. Such shear reinforcement is in addition particularly useful when unbalanced moments are transferred from the slab to the columns, which is a phenomenon typically detrimental for the punching shear resistance of inner connections. Despite the practical relevance of this case, there is currently no experimental evidence on the response of shear-reinforced slabcolumn connections with adjacent openings and moment transfer. Design is thus performed on the basis of simplified rules, modifying the resistance of connections without openings. In the present study, a comprehensive test programme addressed at this issue is presented in an effort to improve the current state-of-knowledge. Five slabs representing several practical cases and potential arrangements of shear reinforcement were tested. The experimental results are investigated in detail and compared to codes of practice, highlighting a number of deficiencies of current simplified rules. The phenomena is finally investigated on the basis of the mechanical model of the Critical Shear Crack Theory, showing a general frame for modelling and design of such detail.