Civil Engineering Reference
In-Depth Information
0
:
606
29,792
275
1
Then,
N
b
,
Rd
¼
¼
4,513,488N
:
1
N
b
,
Rd
¼
4513
:
5kN
>
N
Ed
¼
4195
:
1 kN Then O
ð
:
K
:
Þ
4.3.3.21 Design of the Compression Vertical Member V
1
member is of great importance for this through bridge since it carries not
only the high compressive force coming from the supports but also
a bending moment coming from the analysis of the end portal frame.
The end portal frame is necessary for this through bridge to transfer wind
load coming from the upper wind bracing to the bearings. The reactions
coming from the upper wind bracing cannot be resisted by cross bracing
since it will cause an obstacle to passing traffic. Therefore, these reactions
can be transferred as shown in
Figure 4.75
by an end frame action. The
end frame consists of the first vertical members of the main trusses, the edge
cross girder, and the edge member of the upper wind bracing, which has to
be an I-shaped beam section. The end portal fame can be analyzed as shown
in
Figure 4.75
by assuming hinges at a distance varying from 1/3 to 1/2 of
the depth of the frame. The first vertical member V
1
carries the compressive
design force coming from the analysis of truss under vertical dead and live
loads, which is equal to
5240.8 kN in addition to an added compressive
force of
5240.8 kN and a bending moment of 2178.3 kN m coming from
the analysis of the end portal frame. Let us assume the cross section shown in
Figure 4.76
, which is a compact class 1 cross section. The resistance to
bending moment can be calculated as follows:
W
pl
f
y
g
M0
M
c
,
Rd
¼
for classes 1 and 2
W
pl
¼
55
30
2
5
30
2
4
40
30
2
4
¼
11,875 cm
3
=
4
2
2
:
=
=
11875
10
3
W
pl
f
y
275
M
c
,
Rd
¼
g
M0
¼
¼
3265
:
>
:
6kNm
2178
3kNm
0
10
6
1
:
On the other hand, the resistance to compressive forces can be calculated
as follows:
A¼
2
55
5+2
30
5
¼
850 cm
2
¼
192,083
I
x
¼
2
5
30
3
12 + 2
55
5
3
5
2
3cm
4
=
=
12 + 55
5
17
:
:
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