Design for shear at closely offset planted columns

Transfer slabs are commonly used in multi-storey buildings to accommodate changes in column position between floors. Despite this, the design of transfer slabs with closely offset columns for shear has received little attention from researchers. The paper summarises the results of an experimental campaign in which eight slabs were tested to investigate the punching resistance of transfer slabs with closely offset columns. The tested slabs were centrally supported and simultaneously loaded with a pair of point loads simulating closely offset planted columns and around their perimeter to simulate “field” shear from uniform loading on the transfer slab. The test results are shown to compare well with the predictions of a previously calibrated nonlinear finite element modelling procedure using 3D solid elements. The NLFEA modelling procedure is subsequently used to model a series of subassemblies extracted from a full scale five-storey building with a transfer slab at first floor level. The parametric study considers the influences on the upper column failure load of the gap between the planted and lower columns, the ratio between the upper column load and field shear, concrete strength, and shear reinforcement. A strut and tie model (STM) is developed for the calculation of planted column failure load. The STM is used to model the subassemblies previously analysed with NLFEA and the results of the two approaches are shown to compare well.