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196
IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 2
Design model and recommendations of column-foundation connection through socket with rough interfaces
value
min
N
at the column bottom, given, respectively, by:
(30)
d
max
N N
-=
(31)
cp
c
d
min
A
AN N
-=
To determine the column longitudinal reinforcement, the largest
values of the bending moment and the normal force acting at the
section of column top are considered. For the transverse reinforce-
ment, the column bottom section, where the maximum shear force
is found to act, must be used. The determination of this reinforce-
ment must consider shear concrete strength.
Besides determining the column reinforcements, whichever analy-
sis model is employed, it is recommended that the column longi-
tudinal reinforcement be properly anchored to the column base,
and the vertical reinforcement of rear transverse wall be detailed
by over lapping the reinforcement, in order to transfer the tensile
force of column in proper form to the rear wall. Experimental results
obtained from specimens tested by Canha [4] and Jaguaribe Jr. [9]
confirm that for adequate transfer of force from the column to the
socket, the minimum embedded length for column-socket founda-
tion elements with rough interfaces must meet the NBR-9062:2006
[6] requirements.
Figure 11 – Adapted design model proposed for analysis of the precast column base (Campos et al. [3])
As for smooth interfaces, the determination of the anchored length
of the column longitudinal reinforcement is given by equation 32
based on recommendations by Leonhardt and Mönnig [15]. The
stress transferred from reinforcement to concrete from this point of
anchorage was confirmed experimentally for smooth specimens by
Ebeling [16] and extrapolated here for rough specimens.
(32)
2
emb
anc
l
l
=
3.2 Adaptation of model considering friction forces
Campos et al. [3] proposes a strut-and-tie model applicable to the
analysis of smooth precast column base, which was based on ex-
perimental results of Ebeling [16]. This model was adjusted with that
proposed by Canha [4] for the design of smooth interface sockets con-
sidering the strength of concrete in the determination of internal forces
and subsequently in calculating the transverse reinforcement. The
adjusted model with the proposed modifications is given in Figure 11.
The pressure on the front transverse wall H
topf
, the pressure on the
rear transverse wall H
bot
, and the normal reaction on the foundation
base N
fb
, defined by the equilibrium equations, are given, respec-
tively, by equations 33, 34 and 35:
(33)
a × +m
÷ ÷
ø
ö
ç ç
è
æ
a × +
+ -
+
m+
m
×
+ ÷ ÷
ø
ö
ç ç
è
æ
+ -
-
m+
m
×
+
+ -
=
tg2
tg2
eh5.0d
y
1
V
eh5.0d
e
1
N
eh5.0d
M
H
nb
2
d
nb
nb
2
2
d
nb
d
topf