Basic HTML Version
184
IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 2
Design model and recommendations of column-foundation connection through socket with rough interfaces
The Figure 2 presents the following parameters:
e
sk
:
Distance between the shear key axes
e’
sk
:
Internal distance between shear keys
h
sk
:
Shear key height
l
sk
:
Largest shear key base dimension
l
’
sk
:
Smallest shear key base dimension
a
sk
:
Inclination of shear key face relative to a parallel line through
the joint axis
l
sk
:
Ratio of largest base dimension to height of shear key
q
sk
:
Inclination of shear key face relative to a perpendicular line
through the joint axis.
The geometrical ratio of the shear key can be defined according
to equation 2:
(2)
sk
sk
sk
h/
l
=l
The main results obtained on applying the model proposed by Riz-
kalla et al. [7] are presented in Figure 3.
Figure 3(a) shows an increase in shear strength as the face angle
of shear key
a
sk
decreases up to the limiting value of
a
sk, lim
for which
the smallest shear key base dimension
l
sk
’
is null. This value of
a
sk,
lim
was found to be 45
o
and 35
o
for small and large shear keys, re-
spectively. It is worth pointing out that, according to Lacombe and
Pommeret [8], when this angle is less than 45
o
, the failure of the
connection takes place by slipping between the shear keys.
By increasing
l
sk
and keeping the shear key height h
sk
and the
angle
a
sk
fixed, the value of
l
sk
increases, thus resulting in an de-
crease in shear strength as illustrated by Figure 3(b). Still relative
to
λ
sk
, it is noticed that the strength decrease is more pronounced
along the first part of the curve up to the limiting value of
l
sk
=6
indicated by Lacombe and Pommeret [8], and from this point, the
strength is small and then tends to a constant value for large
values of
l
sk
. According to Figure 3(c), the increase in
l
sk
as h
sk
decreases is also one of the reasons for the observed decrease
in shear strength V.
By varying the number of shear keys n
sk
, the distance between
keys e
sk
is observed to decrease as the number of shear keys in-
creases, consequently resulting in an increase in shear strength V,
as illustrated by Figure 3(d).
Based on the theoretical study of the Rizkalla et al. [7] model, it
is expected that a geometrical ratio of the key
l
sk
≤
6
provides
appropriate stress transfer at the column-pedestal wall inter-
face. Adopting shear keys with angle
a
sk
= 45
o
, internal spacing
e’
sk
=
4cm
and the maximum ratio
l
sk
= 6
to account for
shear key symmetry on the reverse side of the interface, a
suitable shear stress transfer occurs between the column and
the socket.
The Brazilian Standard Code NBR 9062:2006 [6] recommends a
minimum roughness of
h
sk
=
1cm
for every 10 cm of joint in or-
der to assure a monolithic behavior of the connection. However, it
does not specify what distance this 10 cm of joint refers to. Hence,
the 10 cm will be considered here to represent the sum of the larg-
est shear key base dimension
l
sk
and the internal spacing between
the shear keys
e’
sk
, thus resulting to a single key for each joint
length considered, as illustrated in Figure 4(a).
For minimum shear key dimensions, it is recommended that the
these keys provide an additional portion of the interface shear strength
on account of interlock mechanical fraction of the adherence. None-
theless, besides those provided by NBR 9062:2006 [6], there are still
no known specific recommendations for the analysis of these keys
which guarantee an appropriate transfer of load in rough connections.
In order to substantiate the adopted shear key dimensions of the
rough column-socket connection tested by Canha [4], the theoreti-
cal model illustrated in Figure 1 proposed by Rizkalla et al [7] was
used for the qualitative and systematic analysis of the geometric
parameters of the shear keys. This model is commonly used for
shear strength analysis of shear walls with shear keys and fixed
together by dry mortar (“drypack”). The model was then adjusted
with experimental tests carried out on specimens with smooth in-
terface and with two shear key configurations labeled small and
large shear keys. Based on the observed post-cracking behavior
of the specimens, the maximum shear load (V) of the connections
with shear keys can be estimated according to equation 1. In this
equation, the first term represents the compressive strength of the
concrete strut between diagonal cracks (
c
V
) while the second
term refers to the strength due to friction along the sliding surface
(
f
V
). The shear key geometrical parameters are given in Figure 2.
(1)
( )
(
)
(
)
c
cs
cr
sk
c n
c
cs
cr
sk
cos Af1 n A
sen Af1 n V
a
- - sm+a
- =
Where:
n
sk
is the number of shear keys
f
cr
is the compressive strength of the cracked joint
ch
j
ch
j
2
1
cs
cos /b) h h(
A
q
+ =
is the average transverse section of the
diagonal section of the concrete strut
)h/
(
tan
j
ch
1
c
l
-
=a
is the inclination of the diagonal section of the
concrete strut relative to the horizontal.
Figure 2 – Shear key variables (Canha [4])
sk
a
sk
sk
sk
h
'
sk
q
e'
sk
e
sk