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Created by :- Nishant patel
Index
•Introduction •Function of bridge•Main element•Forces exceed on the bridge•Examples
A suspension bridge is a type of bridge in which the deck (the load-bearing portion) is hung below suspension cables on vertical suspenders. The first modern examples of this type of bridge were built in the early 19th century. Simple suspension bridges, which lack vertical suspenders, have a long history in many mountainous parts of the world.
This type of bridge has cables suspended between towers, plus vertical suspender cables that carry the weight of the deck below, upon which traffic crosses. This arrangement allows the deck to be level or to arc upward for additional clearance. Like other suspension bridge types, this type often is constructed without false work.
FUNCTION OF A BRIDGE
To connect two communities which are separated by streams, valley, railroads, etc.
•Suspension bridges are used for highways , where the span of a bridge is more than 200m.
i. Main cable
ii. Suspenders
iii. Decking and stiffening girder
iv. Supporting tower
v. Anchor cable
A
VA VB
B
T T
HH
W KN/m
reaction Horizontal8
8
48
228
2
2
2
22
2
d
wLdH
wLdH
wLwLdH
LwLwLdH
wLVV BA
Equation of horizontal reaction
Taking moments about c, on the right side of c
ß
p
B
H
T
Tw kN/m
?
The cable tension T at any end is the resultant of vertical and horizontal reaction at the end.
2
2
2
422
22
161
2
64)
2(
)8
()2
(
d
LwLT
d
LwwLT
d
wLwLTTT BA
T= Tension at any point p of the cable
Ɵ=Inclination of the tangent at p with horizontal consider equilibrium of part PB
Resolving the forces on this part horizontally.
Minimum tension in cable will occur at c
cos TH
HTT c min
Maximum tension in cable will occur at ends
The inclination β of T with vertical is given by,
2
2
max
161
2 d
LwLT
d
LwL
d
wL
42/
8V
Htan
2
Under the uniformly distributed load the cable takes the from of a parabola
The equation of cable , with either support as origin will be,
)(4
2xLx
L
dy
The equation of parabola, with c as the origin can be written as ,
Consider an element of length ds of the curve, having coordinates x and y.
2
2
2
8
4
L
xd
dx
dy
xL
dy
dxL
xdds
L
xdL
xd
dx
ds
L
xd
L
xd
dx
ds
dx
dydxds
dydxds
4
22
4
224
22
2
1
4
22
4
22
2
22
321
of powershigher negleting
and theorembinominalby Expanding
64
2
11
641
641
1
Total length of the cable,
cable. theoflength Total 3
8
3
4
22
3
322
3212
2
4
32
2
0
3
4
2
2
0 4
22
L
dLS
L
Ld
LS
x
L
dxS
dxL
xdS
L
L
the main cables attach to the ends of the deck, rather than to the ground via large anchorages. The design is well-suited for construction atop elevated piers, or in areas of unstable soils where anchorages would be difficult to construct.
There are generally two arrangement used
1. The suspension cable can be passed over the guide pulley for anchoring it to the other side
2. The suspension cable and anchor cable can be attached to a saddle mounted on rollers.
ß1 ß2
suspension
cableAnchor
cable
ß2 ß1
Anchor
cable suspencion
cable
Guide pulley arrangement
Saddle on roller arrangement
21 coscos TVp
21 sinsin THp
1
2
In case of saddle on roller arrangement, rollers do not have any horizontal reaction. Therefore, the horizontal components of the tensions in the suspension cable and the anchor cable will be equal.
The vertical pressure on the top of the pier is,
HTT 2211 sinsin
2211 coscos TTVp
SUNSHINE SKYWAY BRIDGE, USA
Completion Date: 1987 Cost: $244 Million
Length: 29,040 feet Type: Cable Stayed
Materials: Steel, Concrete Span: 1200 feet
AKASHI KAIKYO BRIDGE, JAPAN
Completion Date: 1998 Cost: $4.3 billion
Length: 12,828 feet Type: Suspension
Materials: Steel Span: 6,527 feet
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