PUNCHING SHEAR OF FLAT SLABS WITH OPENINGS, MOMENT TRANSFER AND SHEAR REINFORCEMENT

flat slabs, openings, moment transfer, shear reinforcement, CSCT

Openings in flat slabs near to columns are often needed to supply the building with utilities. The presence of these openings can lead to a decrease of the punching resistance which is related to (i) the reduction of the control perimeter, (ii) the stress concentrations at the edges of the openings, (iii) the reduction of the unitary shear resistance caused by increased flexural deformations and (iv) the moment transfer in the slab connection in case of unsymmetrical openings. The impact of openings on punching shear resistance depends on their geometry, location, number, and size. Although current code approaches consider a reduction in the control perimeter, there is a lack of sufficient experimental evidence and certain effects are disregarded in design codes. Furthermore, the available literature on slabs with openings and unbalanced moments is limited. Despite the common use of shear reinforcement to enhance punching resistance, there is a surprising absence of published experimental work on shear-reinforced interior connections with openings and unbalanced moments. This study presents three experimental programmes focusing on flat slabs with openings. The first consists of eight interior slab-column connections with axis-symmetric loading and openings at different locations and dimensions. The second consists of nine interior slab-column connections with openings at different locations and dimensions, subjected to different unbalanced moment orientations and eccentricities, and without shear reinforcement. The last series of experimental tests consists of five slabs with openings and moment transfer, representing

several practical cases and potential arrangements of shear reinforcement. Additionally, ix

this work proposes a new approach and a new definition of the control perimeter to improve the prediction of the punching shear resistance of slabs with openings based on the results of the database, previous studies, and linear-elastic analyses of the shear force distribution along the control perimeter. Simple and refined approaches of the Critical Shear Crack Theory are suggested and validated with experimental results to consider the redistribution of forces caused by the openings and/or moment transfer.