Influence of moment redistribution and compressive membrane action on punching strength of flat slabs

Abstract

Type of publication:Peer reviewed journal article The punching shear strength of interior column connections of flat slabs has traditionally been investigated with isolated test specimens subjected exclusively to hogging bending moments. However, the behavior of such specimens is different from that of actual flat slabs, as the potentially beneficial phenomena of moment redistribution between hogging and sagging moments and compressive membrane action cannot take place in the conventional experiments. In the present paper, an axisymmetric numerical model is introduced that allows analyzing the role and significance of these effects on the flexural deformations of continuous flat slabs. Combined with the failure criterion of the Critical Shear Crack Theory, this model can be used to predict the punching capacities of such slabs. Comparisons are made to the results of some unconventional punching tests from the literature showing sound agreement between the modeling results and the experimental observations. The results suggest that the punching capacity of continuous slabs with low amounts of flexural reinforcement in the interior column regions may be underestimated in the current codes of practice.

Internal slab-column connections under monotonic and cyclic imposed rotations

“…8a and b). Modelling the slab only until 0.22L (setup (b) and setup (b) mod ) results in a softer flexural behaviour than the continuous slab; this has already been demonstrated for the case of vertical loads alone [28]. The difference in stiffness between setup (b) and setup (b) mod results from the additional edge reinforcement that is provided in setup (b) mod .…”

“…The influence of the boundary conditions on the deformation capacity of slabcolumn connections has been demonstrated by previous numerical studies, under both vertical load [28] and combined vertical load and transferred moment [29]. It is therefore essential to evaluate the capacity of each setup to reproduce the behaviour of slabcolumn connections of the prototype building.…”

Punching Shear Capacity of Continuous Slabs

“…Only a few analytical models for punching address this effect. 8,11 Compressive membrane action (CMA)…”

“…These specimens model the negative (hogging) moment area around a column, support, or loading point (isolated from the rest of the continuous slab), where the only redistribution possible is that between radial and tangential moments. Although such tests are affordable and relatively easy to perform, results of experiments [2][3][4][5][6][7] and nonlinear analyses [8][9][10] of slabs with rotational and in-plane edge restraints have shown that isolated test specimens may not suitably model the behavior and strength of actual continuous slabs. This is caused by the fact that continuous slabs exhibit two phenomena that cannot appear in isolated specimens, namely redistribution between negative (hogging) and positive (sagging) moments and compressive membrane action (CMA), which may increase the flexural and punching capacity of the slab.…”

“…1(b)). 8,17 A zone with tangential tensile forces (tension ring) forms in the uncracked (and therefore stiffer) part of the slab. This induces compressive stresses in the hogging moment area that increase its flexural strength and stiffness ( Fig.…”