Advanced analytical and numerical modelling of composite slab-column joints

The problem of slab-column joints modelling has been considered many times to find the most adequate methods for prediction of slabs' resistance to punching. The base of considerations was the results of experimental tests. The punching shear was very often considered separately from the flexural capacity of slabs. Such separated calculations are still recommended in most of the Standards. The simplified approach concerning mechanism of punching shear failure as a pure exceeding of the diagonal tensile strength in concrete is too far from the observations in reality. In models of interior slab-column joint the inclined cracks around the column usually form at a load of 55% to 65% of the real ultimate punching load. It means, the solution of the punching problem depends on the post-cracking equilibrium between flexural reinforcement in tension zone and concrete in compression zone in the vicinity of the column face. The idea of composite joints with use of combined head-and-column precast members from high-strength concrete has been proposed by AJDUKIEWICZ and KLISZCZEWICZ (1993) to improve the carrying capacity of interior joints without shear reinforcement. To clarify the doubts about behaviour of such joints and to record the ultimate punching load the full-scale tests have been undertaken. On the basis of observations recorded at tests the analytical model was built up, and separately the numerical tests were done with use of ANSYS software.