Civil Engineering Reference
In-Depth Information
3
2
/
4
(
2.5
)
]}
(
0.51
)
=
8.21 in.
2
Path A-B-C-D1-E2:
A
n
=
8.82
−{
3
(
1
)
−
2
[
8.31 in.
2
Path A1-C-E1:
A
n
=
8.82
−
1
(
1
)(
0.51
)
=
3
2
/
4
(
2.5
)
]}
(
0.51
)
=
8.26 in.
2
Path A1-C-D1-E2:
A
n
=
8.82
−{
2
(
1
)
−
1
[
15.60 in.
2
(88.4% of
A
g
)
.
Therefore, for the member U1-L1:
A
n
=
2
[
7.80
]=
6.2.1.2 Effective Net Area,
A
e
, of Tension Members
Shear lag occurs at connections when the tension load is not transmitted by all of
the member elements to the connection. Therefore, at tension member connections
with elements in different planes (splices, flanges of channels with web only con-
nected, angles with only one leg connected, webs of I-sections with only the flanges
connected), an effective area is determined to reflect that the tensile force is not uni-
formly distributed across the net area at the connection (
Figure 6.1)
.
Shear lag effects
are related to the length of the connection and the efficacy of the tension member
with respect to the transfer of forces on the shear plane between the member and
the connection plate (Munse and Chesson, 1963). The connection efficiency,
U
c
,is
describedbytheratiooftheeccentricity,
e
x
,(thedistancebetweenthecenterofgravity
of connected member elements and the shear plane) and connection length,
L
c
,as
1
.
e
x
L
c
U
c
=
−
(6.6)
Therefore, when a joint is arranged such that not all of the member elements in the
connection are fastened with bolts or with a combination of good quality longitudinal
and transverse welds, the effective net area,
A
e
,is
A
e
=
U
c
A
n
,
(6.7)
U
c
is the connection efficiency or shear lag reduction factor
0.90.
AREMA (2008) recommends shear lag reduction factors,
U
c
, between 0.75 and
1.00, depending on weld length for connections between members and plates that use
only longitudinal welds.
≤
L
c
T/2
T
e
x
T/2
FIGURE 6.1
Shear lag at tension connection.
