Punching resistance of flat slabs loaded with closely offset planted columns

For architectural reasons, transfer slabs supporting closely offset planted columns are often encountered in mixed-use residential buildings. Despite this, the shear resistance of such connections has not been considered by researchers up to now. This paper presents the findings of an experimental campaign that investigated the shear resistance of slabs simulating transfer slabs loaded with closely offset planted columns without shear reinforcement. The tested slabs were simultaneously loaded around their perimeter and adjacent to the central support. Investigated parameters included the gap between the upper and lower columns (taken as 0, 0.5d and d, where d is the slab effective depth), the perimeter load and the relative width of the upper and lower columns. Measurements included applied loads, slab vertical displacements and rotations, changes in slab thickness, strain, and crack width. Following testing, the slabs were saw cut in half to reveal the internal cracking patterns. The experimentally determined failure loads are shown to compare well with the predictions of nonlinear finite element modelling with 3D solid elements and a strut and tie model (STM) developed in the paper.