A presentation on Suspension bridge

2. SUSPENSION BRIDGES

3. INTRODUCTION
The Bridge is a structure
carrying a road, railway, path
etc., across an obstacle (Ex:-
River)
There are various designs of
Bridge to span different
lengths.
The Bridge is designed in such a
way that all the forces acting
on it are transferred to the
ground.
Bridge designers in other words
are Force Balancers.

4. TYPES OF BRIDGES
1)BEAM BRIDGE 2)ARCH BRIDGE
3)TRUSS BRIDGE 4)CANTILEVER BRIDGE
5)SUSPENSION BRIDGE 6)CABLE STAY BRIDGE

5. BEAM BRIDGES
 Beam Bridges are simplest kind of Bridges.
 These Bridges consist of Horizontal with
supports usually on either ends.
 They are constructed for short span
requirements.
 The weight of Bridge and any traffic on it is
directly supported by Piers.
 In Beam Bridges the top side of the deck is
under compression while the bottom side
of the deck is under tension.
TRUSS BRIDGES
 Truss Bridge is a sub-type of Beam Bridge.
 To increase the bridges strength designers
introduced truss to Bridges Beam.
 The Truss of a Beam is a structure of
connected elements usually forming
Triangular units. The Triangles help to
distribute the weight of the vehicles
 The connected elements (typically straight)
may be stressed from tension,
compression , or sometimes both in
response to dynamic loads

6. ARCH BRIDGES
 Arch bridges are arch shaped and
have abutments at each end.
 The Arch Bridge does not need
additional supports or cables. In fact
it’s the shape of structure gives it the
strength.
 The forces on Arch bridge are only
compression forces.
 The weight on the bridge is carried to
abutments at either side.
 Usually they are made for short span
range . But often set end to end to
form a large total length.

7. CANTILEVER BRIDGE
A Cantilever Bridge is a Bridge built using Cantilevers,
Structures that project horizontally into space, supported
only on one end.
For small foot bridge , the cantilever may be simple
beams ; However large cantilever Bridges are designed
using trusses.
 In the structure of Cantilever bridge at least one portion
acts as an anchorage for sustaining another portion which
extends beyond supporting pier.
 A simple Cantilever span is formed by 2 Cantilever arms
extending from opposite sides of an obstacle to be
crossed. The Cantilever arms do not meet in center ,
instead they support a central suspended span which rests
on the ends of Cantilever arms. The suspended span may
be built off site and lifted into place.
All the weight in the middle of bridge is pushed towards
piers and abutments which distribute the weight.
It can span distances over 460m (1500 feet).

8. SUSPENSION BRIDGE
The deck (traffic way) of Suspension Bridge is hung by
Suspender cables which hang from master cables.
The Suspension (main) cables are secured into solid Bed Rock
(If available at sight) or into Concrete blocks called Anchorages on
both ends of the bridge to stabilize structure and are key to the
structure.
The sequence of force transmission for a suspension bridge is
1.To the Deck 2.To the Suspender cables
3.To the main cable 4.To the Bridge tower
5.To the foundation
CABLE-STAYED BRIDGE
A Big drawback of Suspension bridge is that they need to be
anchored to the ground on either side.
A different kind (sub type) of suspension bridge , known as
Cable-Stayed Bridge , does away with this by balancing two sets
of suspension cables on either side of each pier, which supports
load.
Cable stayed bridges are stronger but significantly shorter than
conventional Suspension Bridges and generally do not span
distances much greater than 1 km.
The sequence of force transmission for the Cable-Stayed Bridge
is
1.To the Deck 2.To the Stay cable
3.To the Bridge Tower 4.To the Foundation

9. COMPONENTS OF SUSPENSION BRIDGE

10. ORIGIN
• Rope bridges have been used since
ancient times to cross the rivers.
• They added planks of wood to form
deck that makes bridge easy to cross.
• They used iron chains instead of
ropes to carry heavy loads.
• To flatten the sagging deck they
suspended Bridge from stone towers
and extended the ropes downwards
to level the deck.
• To secure the chains at each end they
anchored the chains to rocky banks
on either side.
• This is how the design of suspension
bridge has originated.
• The first Iron chain suspension bridge
was Jacobs Creek Bridge (1801) in
Pennsylvania; designed by inventor
James Finley.
• The First important modern
suspension bridge is Menai Bridge
(1826) designed by Thomas Telford
which was the first to incorporate all
of necessary components of a
Modern Suspension Bridge.

11. LEAP 1:- STRONGER CHAINS
 In 1845, 300 people
crowd are together
standing on a suspension
bridge in Great Yarmouth.
When all crowd crossed
to one side of a bridge , it
overburdened the chains
and they broke out and
bridge collapsed into the
river drowning 79 people.
 In 1851, when Engineers
are planning 250m
Niagara Bridge, they
replaced Chains with
cables made out of metal
wires to increase its
Strength.

12. LEAP 2:- BUILDING UNDER
WATER
 For Longer spans the
supporting towers must be
built in water.
 In 1874, when Engineers
are planning Brooklyn
Bridge of 486m, the
challenge is to anchor piers
in rushing water below.
 The Solution is Caisson,
which provides working
space for men beneath the
water for excavation.
 Technological advances
now allows to dig out sea
bed foundations using
machinery without risking
the lives of men.

13. LEAP 3:-TALLER
TOWERS
The next breakthrough
came in Golden Gate
Bridge (1280m long.)
The engineers
understood that to
lengthen the roadway
the towers height must
also be raised.
To raise the height of
towers engineers used
hollow steel shafts for
construction of towers
instead of stone.

14. LEAP 4:- WIND
 As the decks got more longer they are
more likely to twist and bend.
 Then for construction of Verrazano
Narrows Bridge of 1298m the design must
resist particularly destructive force THE
WIND.
 In 1940; Tacoma Narrows Bridge in
Washington collapsed due to wind after 4
months from opening date.
 The solution is to introduce stream line
profiles into sides of the deck.
 Since the Verrazano Narrows Bridge is
Double deck bridge stream line profile is
not a solution as it makes currents of air to
collide and produce further destruction.
 So rather than deflecting wind they
decided to resist it by stiffening the deck.
This is done using Open Box Concept.

15. LEAP 5:- EARTH QUAKE
 To build worlds biggest suspension
bridge Akashi Kaikyo Bridge of
3911m engineers have to defeat a
powerful force of nature
EARTHQUAKE.
 Japan is situated in worlds most
seismically active areas.
 The first line of defence from
Earthquakes are the Bridge towers
themselves. They are built of Steel
to make them flexible.
 The second layer of protection are
20 huge pendulums called dampers
in in each towers each of weight 10
tons.

16. CONSTRUCTION
SEQUENCE

17. 1. TOWER CONSTRUCTION
 Tower foundations are prepared by digging down to
a sufficiently firm rock formation.
 Some Bridges are designed so that their towers are
built on dry land, which makes their construction
easier.
 If a tower will stand in water , its construction begins
with lowering a Caisson ( a large watertight chamber,
open at the bottom, from which the water is kept
out by air pressure and in which construction work
may be carried out under water) to the ground
beneath the water; Removing water from the
Caissons interior allows workers to excavate a
foundation without actually working in water.
 When excavation is complete a concrete tower
foundation is formed.
 From the tower foundation , towers of single or
multiple columns are erected using high strength
reinforced concrete , stonework, or steel.
 Concrete is used most frequently in modern
suspension bridge construction due to high cost of
steel.
 Large devices called Saddles, which will carry the
main suspension cables, are positioned at top of
towers.

18. 2. CABLE CONSTRUCTION
 When the towers and anchorages have been
completed, a pilot line must be strung along
the cables eventual path, from one anchorage
across the towers to other anchorage.
 Various methods can be used to position the
pilot line: Ex:- Kites, Helicopters, Boats.
 When the pilot line is in place, a Catwalk is
constructed for bridges entire length, about
1m below the pilot line so workers can attend
cable formation.
 The spinning wheel mounted on the Pilot line
carries the wire across the Bridges path to and
fro between anchorages on either side.
 This process is repeated until a bundle of
desired no of wire strands is formed. (It varies
from about 125 strands to more than 400.)
 During spinning , workers standing on catwalk
make sure it unwinds smoothly, freeing any
kinks.
 When proper number have been spun, a
special arrangement of rapidly positioned
jacks is used to compress the bundles into
compact cable, and then a steel wire is
wrapped around it.
 Steel clamps are mounted around the cable at
predetermined intervals to serve as anchoring
points for vertical cables that will connect the
decking to the support cable.

19. 3.ANCHORAGE
CONSTRUCTION
 Anchorages are structures to
which the ends of bridges
cables are secured.
 They resist the Tension of
cables and form as the main
anchor system for entire
structure.
 The cables are usually
anchored to good quality
rock.
 If there is no solid rock at the
site to secure them into, the
anchor point is built on the
shore line using steel frames
and concrete.

20. 4. DECK CONSTRUCTION
 After vertical cables are attached
to main support cable, the Deck
structure can be started.
 In one technique, a moving crane
that rolls at top of suspension
bridge lifts Deck sections into
place , where workers attach them
to previously placed sections and
to the vertical cables that hung
from main suspension cables.
 Alternatively, the crane may rest
directly on the deck and move
forward as each section is placed.
 The structure must be built in
both directions from support
towers at correct rate in order to
keep the forces on the towers
balanced at all times.

21. 5. FINISHING
 When the Deck Structure is
complete, it is covered with a base
layer (Ex:-Steel plates) and paved
over.
 Painting the steel surfaces and
installing electric lines for lighting
are examples of other finishing
steps.
 In addition, ongoing maintenance
procedures begin.
 For example a permanent staff of
17 iron workers and 38 painters
continue to work daily on Golden
Gate Bridge , replacing corroding
rivets and other steel components
and touching up the paint that
protects the Bridge.

30. CONCLUSION
The design of bridge is to be selected based on
span and site conditions.
When spanning long distances (>1 km) Suspension
Bridge is the only option for Bridge designers.
The Suspension bridges had grown in span up to 4
km using power of Human Ingenuity.
They must be designed very carefully considering
all forces of nature.
Engineers spanned bridges between cities , states
and even Countries and even continents.