Civil Engineering Reference
In-Depth Information
Design Bending Moment (M
Ed
) and Shear Force (Q
Ed
)
M
Ed
¼M
D+L+
F
¼
20,285
:
7kNm
Q
Ed
¼Q
D+L+
F
¼
3132
:
8kN
Design of the Main Plate Girder Cross Section
Let us assume the main plate girder cross section shown in
Figure 4.16
. The
cross section consists of two flange plates for the upper and lower flanges and
a web plate. The web plate height is taken as equal to
L
/10
¼
27,000/
10
¼
2700 mm, with a plate thickness of 16 mm. The width of the bottom
plate of the upper and lower flanges of the cross section is taken as 0.2
the web height, which is equal to 540 mm, while the top plate width
is taken as 500 mm, to allow for welding with the bottom flange plate.
The flange plates have the same plate thickness of 30 mm. The choice
of two flange plates for the upper and lower flanges is intended to curtail
the top flange plate approximately at quarter-span as will be detailed in the
coming sections. It should be noted that the web height value (
L
/10) is an
acceptable recommended [1.9] value for railway steel bridges constructed
in Great Britain and Europe. This value is an initial value for preliminary
cross-sectional estimation. The cross section has to be checked, classified,
designed, and assessed against deflection limits set by serviceability limit
states. To classify the cross section chosen,
s
235
f
y
r
235
275
e ¼
¼
¼
0
:
924
C
1
¼
254mm,
t
fl
¼
60,
C
1
=
t
fl
¼
254
=
60
¼
3
:
2
9
0
:
924
¼
8
:
316 Main plate girder flange is class 1
ð
Þ:
C
2
¼
2684mm,
t
w
¼
16,
C
1
=
t
fl
¼
2684
=
16
¼
167
:
8
>
124
0
:
924
¼
114
:
58 Main plate girder web is class 4
ð
Þ:
To calculate the bending moment resistance, the effective area should be
used. Considering web plate buckling, the effective area of the web part in
compression (see
Figure 4.142
)
can be calculated as follows:
k
s
¼
23
:
9
270
=
1
:
6
l
p
¼
p
23
¼
1
:
315
>
0
:
673
28
:
4
0
:
924
:
9
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