278
IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 2
Experimental and numerical analysis of reinforced concrete mushroom slabs
flexural reinforcement used was the same for all the slabs being
formed by 12.5 mm bars spaced at each 105 mm in x direction and
12.5 mm bars spaced at each 115 mm in the y direction. The con-
crete cover was 15 mm in the upper face and 10 mm the bottom of
the slabs. This series of tests has as main variable the slope of the
column capitals, adopting relations between
h
H
:
l
H
of 1:2, 1:3 and
1:4, in order to assess their influence on the behavior and strength
of slabs. Table 1 shows the characteristics of the tested slabs. The
slabs were subjected to symmetrical loading as shown in Figure 8.
Compressive strains in the concrete surface were measured us-
ing strain gauges placed in the region around the slab-column
connection. The gauges were positioned in tangential and radial
directions, as shown in Figure 9, in which it is possible to notice
that the gauges position varied according to the geometry (slope)
of the capitals. The monitoring of strains was more intense in the
edges of the capitals which are critical areas in terms of stress
concentration.
Table 2 shows test results where it is possible to observe a varia-
tion in the failure load of slabs up to 58.5% (LC1 to LC3). This
variation can be attributed to the addition and the subsequent in-
crease in capitals, once the slab LC1 has capital and the slabs
LC2, LC3 and LC4 had their capitals added and varying its thick-
ness/length ratio of 1:2 to 1:4. Tests showed an increase of 30% of
the failure load of slab LC1 to LC2, which had the smaller column
capital, with 1:2 ratio, as recommended by the EUROCODE 2 [11]
and NBR 6118 [10].In the case of slab LC3, which had a ratio of 1:3
Figure 9 – Strain gages fixed in the bottom surface of slabs
Table 2 – Experimental results of the slabs tested
Slab
d
(mm)
l
H
(mm)
f
c
(MPa)
cmax,in
(‰)
cmax,out
(‰)
r
ys
(mm)
Experimental
Rupture Place
P
u
(kN)
LC1
111,5
-
31
-
-
3,23.d
-
327,0
LC2
112,5
110
-0,92
-2,16
5,02.d
EXT
427,0
LC3
165
33
-3,26
-1,39
5,02.d
INT
518,5
LC4
110,5
220
-4,12
-1,55
6,95.d
513,5
1...,97,98,99,100,101,102,103,104,105,106 108,109,110,111,112,113,114,115,116,117,...190