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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 2
R. M. F. CANHA |
G. M. CAMPOS |
M. K. EL DEBS
showed a similar behavior to that of monolithic connections, hence
resulting in full transfer of the bending moments and normal loads
from column to socket, it is recommended, for the case of rough in-
terface sockets, to apply the bending theory for designing the main
vertical reinforcement. Nonetheless, tests carried out by Jaguaribe
Jr. [9] showed that the estimated connection strength based on
the bending theory for reduced embedded lengths was higher than
experimental strength values obtained from tested specimens.
This indicated that the bending theory is applicable only to sockets
with embedded lengths that meet the criteria given by the Brazilian
Standard Code NBR 9062:2006 [6].
In this paper, a refined model for detailing the vertical reinforce-
ments is presented, originally proposed by Canha [4], with addi-
tional considerations and recommendations, as shown in Figure 7.
For a more precise analysis, it is recommended take into account
all vertical reinforcements contributing to the strength of the con-
nection
.
Besides this, the rectangular-parabolic concrete compres-
sion stress diagram should be adopted.
However, for practical applications, a simplified analysis can be em-
ployed. This approach assumes a simplified diagram of concrete
compression stress with height equal to 0.8 of the depth of the neutral
axis and the resulting tensile force determined by the contribution of
the main vertical reinforcements at the corners of rear wall and the
secondary vertical reinforcements placed in this wall. Hence, the es-
timated total reinforcement based on the bending theory is obtained
from equation 3 and the reinforcement
A
s,mv
is then calculated.
(3)
tsv ,s
mv ,s
tot ,s
A A2
A
+ × =
The secondary reinforcements of rough interface sockets are de-
signed considering the behavior of the longitudinal walls similar to
that of short corbel. It is noted that, in the application of bending
theory, the reinforcement
tsv ,s
A
is included in the calculation of
tot ,s
A
and it is equal to
0.40 . A
s,mv
. This secondary reinforce-
ment is important in socket foundation to resist secondary stresses
and for crack control of the pedestal walls.
Figure 7 shows the following parameters:
M
bd
: Design bending moment at socket base
csf
R
: Resultant of concrete compressive stress of socket
1ssf
ssf
R R
=
: Resultant of forces in vertical reinforcements
tsv,s
mv ,s
A A.2
+
at
sf
1
d d
=
ssfi
R
: Resultant of forces in secondary vertical reinforcements
lsv,s
A
at
i
d
. In the case of secondary vertical reinforcement in
two layers, for instance, there are the following parameters:
2 ssf
R
: Resultant of forces in secondary vertical reinforcements
lsv,s
A
at
2
d
3 ssf
R
: Resultant of forces in secondary vertical reinforcements
lsv,s
A
at
3
d
s
cd
: Design concrete compressive stress of socket
Figure 6 – Positioning of pedestal reinforcements
d
V
A
A
A
s,tmh
A
s,lmh
Section B-B
A
s,lsv
A
s,vm
A
s,vm
A
s,tsv
A
s,tsh
A
s,lsh
rear transv.
wall
longitudinal
wall
front transv.
wall
longitudinal
wall
B
B
Section A-A
A
s,lsv
A
s,mv
A
s,mv
A
s,tsv
d
N
d
M