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