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1. Introduction
Flat slabs are distinguished from conventional beam-and-slab floors
because they are supported directly on columns. This structural sys-
tem is easier to be constructed because forms and reinforcement
are simple, which may generate economic gains due to reductions
in the construction time. The main disadvantage of this structural
system is the possibility of punching shear, which is a brittle local
failure that may spread and lead the whole structure to ruin through
progressive collapse. To improve the ductility and to increase the
bearing capacity of a slab-column connection it is common the use
of shear reinforcements like stud rails, bent-up bars or double-head-
ed studs. Another alternative is to increase the effective depth of
the slab by using column capitals or drop panels, what reduces the
shear stresses in slab-column connections. These elements may
also increase its ductility as the punching strength approaches the
flexural resistance of the slab. Figure 1 shows some possibilities for
slab-column connections and Figure 2 presents a mushroom slab
used in a garage building in Brazil.
1.1 Historic
Flat slabs were developed probably independently in the early XX
century by different engineers. In the U.S.A. C. A. P. Turner was
responsible for demonstrating the efficiency and reliability of the
system (Gasparini [1]). In Europe Robert Maillart, a Swiss engineer
more famous for his works with bridges, is believed to be the inven-
tor of flat slabs (Furst and Marti [2]),but credits are also given to
Arthur F. Loleit, a Russian engineer (Kierdorf [3]).
At that time one of the biggest challenges was to determinate the
stresses in floors with slabs supported directly on columns, without
271 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 2
A. F. LIMA NETO | M. P. FERREIRA | D. R. C. OLIVEIRA | G. S. S. A. MELO
Figure1 – Systems slabs without beams
Flat slab
Mushroom slab (drop panel)
A
C
Mushroom slab (column capitals)
Mushroom slab (drop panel + capital)
B
D