Simplified Punching Shear Design Method for Slab Column Connections Using Fuzzy Learning

INTRODUCTION
Flat plates consist of slabs directly supported on the
columns without beams. For this simple appearance, flat
plate systems have various economic and functional advantages
over other floor systems such as fast construction, low story
height, and irregular column layout. From a viewpoint of
structural mechanics, however, flat plates are structures of
complex behavior. Moreover, flat plates usually fail in a
brittle manner by punching at the slab-column connections
within the discontinuity region known as the D-region.
1,2
At
these connections, three-dimensional stresses are developed
due to the combined high shear and normal stresses creating
a stress state that is complex to analyze accurately.
3
For the last three decades, a significant amount of research
has been performed to investigate this complex problem of
concentric punching shear of reinforced concrete flat plates
by using various methods ranging from mechanical models
up to purely empirical models. In early models including
Yitzhaki
4 and Long and Rankin,
5 punching shear strength
was defined considering the flexural capacity of reinforced
concrete slabs. This was based on the experimental observation
that the punching shear strength was close to the flexural
capacities of the concrete slabs. Pralong6
and Nielsen7
derived lower bound and upper bound values for punching shear
strength based on the theory of plasticity. These formulations
did not consider the effect of flexural reinforcement on the
punching shear strength. Kinnunen and Nylander
8
developed
the first mechanical model for punching shear strength using
failure criteria based on the observation of shear cracks in the
experiments. In this model, the failure criteria were defined
by the inclined radial compressive stress and the tangential
compressive strain at the shear crack. Even though Kinnunen
and Nylander’s model
8
did not provide high accuracy in
punching shear strength predictions, it significantly contributed
to a better understanding of the failure mechanism of the
slab-column connections and enabled visualizing a rational
flow of forces in such connections. Alexander and
Simmonds
2
proposed a strut-and-tie model with concrete ties
to describe the load transfer in the slab-column connections.
Bažant and Cao9 developed a punching shear strength model
considering size effect of concrete based on principles of
fracture mechanics. The size-effect model was able to
explain the experimental observations of decreasing
punching failure shear stresses of slab-column connections
without reinforcement with increasing slab thickness.
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