Civil Engineering Reference
In-Depth Information
T
max
L
2
/2
a
B
6m
A
18 m
10
L
2
C
H
L
1
L
2
F
IGURE
5.8
Suspension cable
of Ex. 5.4
200 m
Then, from Eq. (5.16)
110
.
1
2
10
×
H
=
=
3367
.
2kN
2
×
18
The maximum tension follows from Eq. (5.19), i.e.
(10
110
.
1)
2
3367
.
2
2
T
max
=
×
+
=
3542
.
6kN
Then, from Eq. (5.20)
×
tan
−
1
10
110
.
1
3367
.
2
18
.
1
◦
at B
α
max
=
=
SUSPENSION BRIDGES
A typical arrangement for a suspension bridge is shown diagrammatically in Fig. 5.9.
The bridge deck is suspended by hangers from the cables which pass over the tops of
the towers and are secured by massive anchor blocks embedded in the ground. The
advantage of this form of bridge construction is its ability to provide large clear spans
so that sea-going ships, say, can pass unimpeded. Typical examples in the UK are the
suspension bridges over the rivers Humber and Severn, the Forth road bridge and the
Menai Straits bridge in which the suspension cables comprise chain links rather than
tightly bound wires. Suspension bridges are also used for much smaller spans such as
pedestrian footbridges and for light vehicular traffic over narrow rivers.
The major portion of the load carried by the cables in a suspension bridge is due to
the weight of the deck, its associated stiffening girder and the weight of the vehicles
crossing the bridge. By comparison, the self-weight of the cables is negligible. We may
assume therefore that the cables carry a uniform horizontally distributed load and
therefore take up a parabolic shape; the analysis described in the preceding section
then applies.
