Civil Engineering Reference
In-Depth Information
The shear stress on the welds is
P
A
=
P
2
t
e
(
2
b
+
d)
τ =
(9.7)
Ty
I
p
=
6
(Pe)y
t
e
8
b
3
+
d
3
,
σ
t
x
=
(9.8a)
+
6
bd
2
Tx
I
p
=
6
(Pe)x
t
e
8
b
3
d
3
,
σ
t
y
=
(9.8b)
+
6
bd
2
+
where
x
is the distance from the centroid to the point of interest on the weld in the
x
-direction and
y
is the distance from the centroid to the point of interest on the weld
in the
y
-direction.
The stress resultant at any location on the weld described by locations
x
and
y
is
(
2
τ + σ
t
y
)
2
f
=
+ σ
t
x
.
(9.9)
9.2.4.5.3 Beam Framing Connections
Welded beam framing connections are not used in the main members of steel railway
superstructures due to the cyclical load regime (see Example 9.3). However, when
used on secondary members, such as walkway supports, welded beam framing con-
nections are subjected to shear force,
P
, and end bending moment,
M
e
, on welds
on the outstanding legs of the connection angles. The legs of the connection angles
fastened to the web of the beam are also subject to an eccentric shear force, which
creates a torsional moment,
Pe
(
Figure 9.7)
.
Beam framing connections are often assumed to transfer shear only in usual design
practice(i.e.,itisassumedthatthebeamissimplysupportedand
M
e
=
0). However, in
reality, due to end restraint, some proportion of the fixed end moment,
δ
M
f
, typically
exists (
M
e
/M
f
, where
M
f
is the fixed end beam moment). Welded connection
behavior in structures is often semirigid with a resulting end moment (Blodgett,
2002). The magnitude of the end moment depends on the rigidity of the support.
For example, a beam end connection to a heavy column flange may be quite rigid
(
δ =
1), while a beam end connection framing into the web of a girder or column
may be quite flexible (
δ →
0) (
Figure 9.8).
A rigid connection may be designed for the end moment due to full fixity,
M
f
, and
corresponding shear force,
P
. A semirigid connection will require an understanding
of the end moment
(M
e
)
-end rotation (
δ →
φ
e
)
relationship (often nonlinear) to determine
rotational stiffness and the end moment to be used in conjunction with shear force for
design. Moment-rotation curves, developed from theory and experiment, for welded
joint configurations
∗
are available in the technical literature (e.g., Faella et al., 2000).
∗
Mainly for beam to column flange connections.
