bridge engineering

2. A bridge is a structure that permits us to cross over an obstacle.
Suppose we lay a plank across a brook. If we have a bridge. If the plank is thin in
relation to
its length , it will sag. In fact, if it is too long, it will collapse. This shows that we
must consider the
weight of a bridge itself---the “dead load”.
If we stand at the middle of the plank, it sags even more. So, we
must provide for the weight of whatever our bridge is designed to
carry--- the “live load”.
Also, when you walk across the plank, it bounces under you,
illustrating the effect of a “moving live load”.
Finally, there is a “wind load”. A strong wind pushes against the
sides, lifts the deck, shakes the whole structure. Certainly the force of
the wind is something to keep in mind.
Bridges help us to connect to each other and the world.
There are four main types of physical bridges. They are arch, beam,
suspension and cable-stayed.

3. Functions : aqueduct, viaduct, highway, pedestrian etc.
Materials of construction : reinforced concrete, pre-
stressed concrete, steel, composite, timber etc.
Form of superstructure : slab, beam, truss, arch,
suspension, cable-stayed etc.
Inter-span relation : simple, continuous, cantilever.
Method of construction : pin-connected, riveted, welded
etc.
Span : short, medium, long, right, skew, curved.
Type of service and duration of use : permanent,
temporary bridge, military

4. SUSPENSION BRIDGE
COMPARISION
Advantages over other bridge
types
Longer main spans
Less material may be required than other
bridge types, even at spans they can achieve,
leading to a reduced construction cost
Except for installation of the initial temporary
cables, little or no access from below is required
during construction, for example allowing a
waterway to remain open while the bridge is built
above
A suspension bridge can be made out of
simple materials such as wood and common
wire rope.
May be better to withstand earthquake
movements than heavier and more rigid bridges
Disadvantages over other bridge
types
Considerable stiffness may be
required to prevent the bridge deck
vibrating under high winds
The relatively low deck stiffness
compared to other (non-suspension)
types of bridges makes it more
difficult to carry heavy rail traffic
where high concentrated live loads
occur

5. The two basic parts are:
Substructure - includes the piers, the abutments and the
foundations.
Superstructure - consists of the deck structure itself, which
support the direct loads due to traffic and all the other
permanent and variable leads to which the structure is
subjected.
The connection between the substructure and the
superstructure is usually made through bearings. However,
rigid connections between the piers (and sometimes the
abutments) may be adopted, particularly in frame bridges
with tall (flexible) piers.

6. Bridge is a structure which provides a passage over
a gap without closing the opening which is beneath that gap. The passage
may be due to railway , roadway , canal & natural river etc. Initially the
naturally available materials such as stone and timber were extensively
used for bridges but now days artificial materials such as cement concrete
& steel are utilized more in the construction of bridge.

7. ➢ During the king “harshavardhna” or even before him india appears
to have a good highway system & such highways had a number of
bridge.
➢ “firoze shah” who ruled the delhi in mid 14thcentury built a number
of canal & bridges.
➢ “portuguese” in 16thand 17thcentury built many old arch masonary
bridges in “goa”.
➢ One of oldest stone slab bridge still in use across the river “cauvery”
at “srirangapatnam” bulit by “tippu sultan”.
➢ A number of cable stayed bridges has been built in india in past two
decades. The major one is “vidhyasagar sethu” across “hooghly” at
“kolkata” & “nalini bridge” on river “jamuna” at “allahabad”.
➢ Inidian railways build a number of large steel arch bridge in “j & k”.
➢ BRO has erected a cable stayed bridge in early part of this millenium
which is claimed to be only bridge of the type at highest altitude in
the world at the time of construction.

8. 700 A.D. Asia
1,304 years
ago
100 B.C. Romans
2,104 years ago
Clapper Bridge
Tree trunk
Stone
Arch design
evenly distributes
stresses
Natural concrete
made from mud
and straw
Roman Arch Bridge
Great Stone Bridge in China
Low bridge
Shallow arch
Allows boats
and water to pass
through

9. Truss Bridges
Mechanics of
Design
Wood
Suspension Bridges
Use of steel in
suspending cables
1900
1920
Prestressed
Concrete
Steel
2000

10. MASONARY ARCH BRIDGE
Probably first category of bridge to be involved.
Aesthetically superior to slab bridges.
Consist of a arch shape slab supported on two apposite wall & it
was adopted earlier for small of 3 to 15m in masonry & extended
up to 519m in steel & 305m in concrete has been built in the world.

11. Beam Bridge
When something pushes down on the beam, the beam bends.
Its top edge is pushed together, and its bottom edge is pulled
apart.
Beam bridges are horizontal beams supported at each end by
substructure units and can be either simply supported when the
beams only connect across a single span, or continuous when
the beams are connected across two or more spans.

13. PIPE CULVERT
Consist of a pipe barrel under the embankment with protection
works at the entry and exit.
It is suitable for cross drainage flow on relatively flat terrain & in
this discharge is limited & it has negligible maintenance

14. □ Hydraulically short conduit which
conveys stream flow through a roadway
embankment or past some other type of
flow obstruction

15. SLAB BRIDGE
Simplest type of construction.
Adopted for small bridges and culverts.
Span is between 10-20m.
Concrete slab cast monolithically over longitudinal girder.
No.of longitudinal girders depends upon the width of road

16. PLATE GIRDER BRIDGE
□ Span ranges 10 to 60m.
□ Can be extending up to 250m in
continuous construction

17. TRUSS BRIDGE
□ Span 30 to 375m in simply supported
case.
□ Span 30 to 550m in cantilever
combination case

18. All beams in a truss bridge are straight. Trusses are
comprised of many small beams that together can support
a large amount of weight and span great distances.

19. SUSPENSSION BRIDGE
Made up of high tensile steel cables strung in form of a
centenary to which the deck is attached by steel
suspenders which are made up of steel
rods/members/cables.
Deck can be of timber , concrete or steel spanning
across the stiffening girders transmitting loads to
suspenders.

20. Forces
In all suspension bridges, the roadway hangs from massive
steel cables, which are draped over two towers and secured
into solid concrete blocks, called anchorages, on both ends of
the bridge. The cars push down on the roadway, but because
the roadway is suspended, the cables transfer the load into
compression in the two towers. The two towers support most of
the bridge's weight.

22. ➢ Cable-stayed bridges like suspension bridges, are held
up by cables. However, in a cable-stayed bridge, less
cable is required and the towers holding the cables are
proportionately higher.

23. Similar to suspension bridge except that there will be no
suspenders in the cable stayed bridges .
A number of cables are stretched from support tower directly
connected the decking.
The cable stayed bridge is newer than the other types of
bridge. Large upright steel supports are used to transmit the
load into the ground.

24. □ A cantilever bridge is a bridge built
using cantilevers: structures that project
horizontally into space, supported on
only one end.

25. ➢ Cantilever bridges are built using cantilevers horizontal beams
supported on only one end. Most cantilever bridges use a pair
of continuous spans that extend from opposite sides of the
supporting piers to meet at the center of the obstacle the bridge
crosses.

26. The arch has great natural strength. Thousands of years
ago, Romans built arches out of stone.Today,most arch
bridges are made of steel or concrete,and they can
span up to 800 feet.

27. Arch bridges
have abutments at
each end. The weight
of the bridge is thrust
into the abutments at
either side.

28. Forces
The arch is squeezed together, and this squeezing force is
carried outward along the curve to the supports at each
end. The supports, called abutments, push back on the arch
and prevent the ends of the arch from spreading apart.

29. ➢A movable bridge, is a bridge that moves to
allow passage usually for boats or barges.

31. Based upon type of structural arrangement
➢I-girder bridge
➢Plate girder bridge
➢truss girder bridge
➢Suspension bridge

32. Based upon structural action or nature of
superstructure action
➢Simply supported span bridge
➢Continuous span bridge
➢Cantilever bridge
➢Arch bridge
➢Rigid frame bridge

33. Based upon type of connections
➢Riveted bridge
➢Welded bridge
➢Bolted bridge
➢Pinned bridge

34. Based upon floor action
➢Deck type bridge
➢Through type bridge
➢Semi –through type bridge or pony
bridge
➢Double deck bridge-used in rail cum
road bridge

35. Based upon movement of structural parts of
the bridge
➢Fixed(permanent) bridge
➢Movable bridge: Can opened either
horizontally or vertically so as allow the
river or channel traffic to pass

36. Based upon purpose of bridge
➢Road bridge
➢Railway bridge
➢Pedestrian bridge

37. Based upon loading
➢IRC class AA loading bridge
➢IRC class A loading bridge
➢IRC class B bridge
.

38. Base upon span length
➢Culvert – up to span length 6m
➢Minor bridge – up to span length 6 to
30m.
➢Major bridge – up to span length over
30m

39. 700 A.D. Asia
100 B.C. Romans
Natural Bridges
Clapper Bridge
Tree trunk
Stone
Natural
Cement
Roman Arch Bridge
The Arch
History of Bridge Development
Great Stone Bridge in China
Low Bridge
Shallow Arch
1300 A.D. Renaissance
Strength of
Materials
Mathematical
Theories
Development of
Metal

40. First Cast-Iron Bridge
Coalbrookdale,
England
1800 A.D.
History of Bridge Development
1850 A.D.
Britannia Tubular
Bridge Wrought Iron
Truss Bridges
Mechanics of
Design
Suspension Bridges
Use of Steel for
the suspending
cables
1900 A.D.
1920 A.D.
Prestressed
Concrete
Steel
2000 A.D.

49. • The most common and basic type
• Typical spans : 10m to 200m

50. • Truss is a simple skeletal structure.
• Typical span lengths are 40m to 500m.

51. Beam Bridge
Basic Beam Bridge Actual
Beam Bridge

53. ➢ A beam or "girder" bridge is the simplest and most
inexpensive kind of bridge.
➢ In its most basic form, a beam bridge consists of a
horizontal beam that is supported at each end by
piers.The weight of the beam pushes straight
down on the piers.
➢ The beam itself must be strong so that it doesn't
bend under its own weight and the added weight
of crossing traffic.
➢ When a load pushes down on the beam, the beam's
top edge is pushed together (compression) while
the bottom edge is stretched (tension).

54. Basic Arch Bridge
Actual Arch Bridge
Bixby Creek Bridge,Monterey, CA

57. ➢Arch bridges are one of the oldest types
of bridges and have great natural
strength.
➢Instead of pushing straight down, the
weight of an arch bridge is carried
outward along the curve of the arch to the
supports at each end.
➢These supports, called the abutments,
carry the load and keep the ends of the
bridge from spreading out.

58. Basic Suspension Bridge

61. ➢ Aesthetic, light, and strong,suspension bridges
can span distances from 2,000 to 7,000 feet --
far longer than any other kind of bridge.
➢ They also tend to be the most expensive to
build.
➢ True to its name, a suspension bridge suspends
the roadway from huge main cables, which
extend from one end of the bridge to the other.
➢ These cables rest on top of high towers and are
secured at each end by anchorages.

62. The towers enable the main cables
to be draped over long distances.
Most of the weight of the bridge is
carried by the cables to the
anchorages, which are imbedded in
either solid rock or massive concrete
blocks.
Inside the anchorages, thecables
are spread over a large area to
evenly distribute the load and to
prevent the cables from breaking
free.

63. Basic Cable-stayed Bridge

66. ➢ Cable-stayed bridges may look similar to
suspensions bridges -- both have roadways that
hang from cables and both have towers.
➢ Two bridges support the load of the roadway in
very different ways.
➢ The difference lies in how the cables are
connected to the towers. In suspension bridges,the
cables ride freely across the towers, transmitting
the load to the anchorages at either end.
➢ In cable-stayeded bridges, the cables are attached
to the towers, which alone bear the load.

67. The cables can be attached to the
roadway in a variety of ways.
In a radial pattern, cablesextend
from several points on the road to
a single point at the top of the
tower.
In a parallel pattern, cables are
attached at different heights along
the tower,running parallel to one
other.