Civil Engineering Reference
In-Depth Information
TABLE E9.1
Location
x
(in.)
y
(in.)
t
e
f
2
(k/in.)
A
4.5
6
2.57
B
1.5
6
2.06
C
1.5
0
1.66
The weld stresses are computed in Table E9.1 for various locations on the
welds on the beam web.
Therefore, the required weld thickness is
2.57
0.28
(
70
)
≥
t
e
≥
0.13 in.
for shear and torsion in the throat of welds on the beam web
2.57
(
17.5
)(
0.707
)
≥
t
e
≥
0.21 in.
for shear and torsion of equal leg welds on the beam web.
Fatigue must be considered if the applied load is cyclical. A connection
such as that shown in
Figure E9.3
is a very poor connection from a fatigue
perspective with an allowable fatigue stress of 8 ksi. In that case, the required
weldthicknessforshearandbendingoftheweldsontheendplatewillgreatly
exceed the maximum allowable fillet weld size based on the thickness of the
thinnest plate or element in the connection.
Eccentrically loaded welded connections should not be used to join members
subjected to cyclical live loads. The very low fatigue strength of these joints (e.g.,
transversely loaded fillet welds subject to tension or stress reversal) makes them
unacceptable for joints in main carrying members. For such joints, bolted connections
are more appropriate.
9.2.4.5.4 Girder Flange-to-Web “T” Joints
A connection such as those shown in
Figure 9.4e
and f transmits horizontal shear
forces from bending and, if present, direct transverse loads. This connection between
girder flanges and web plates may be made with CJP groove welds, PJP groove welds,
or fillet welds using the SAW process. Some engineers specify fillet or PJP groove
welds when the connection is subjected to only horizontal shear from bending. CJP
groove welds may be required when weld shear due to direct loading is combined
with horizontal shear from bending.
The horizontal shear flow,
q
f
, for which the flange-to-web weld is designed, is (see
Chapter 7)
dP
f
dx
=
VQ
f
I
q
f
=
,
(9.14)
where
V
is the maximu
m
shear force,
q
f
=
A
f
y
(statical moment of the flange area
about the neutral axis),
y
is the distance from the flange centroid to the neutral axis.
