What are the components of the bridge? Image result for bridge-engg-components The main components of a bridge are the foundation, substructure, and the superstructure. Each of these core areas have other parts within them. Piles and pile caps are constructed as the foundation of the bridge

1. Transportation Engineering (Bridge
Engineering)
Salman Rabbani
Asst. Professor, CED, MIET, Jammu
B. E. (Civil Engg.) M. Tech. (Structural. Engg.)
LPU Jalandhar GNDEC LUDHIANA

2. UNIT-V
1) Bridges: Introduction, Components, classification and identification.
2) Data Collection, site selection, Economic Span, Estimation of flood
discharge, waterway, scours depth, depth of foundation, Afflux,
clearance and free board.
3) Loads, Forces and Stresses for Bridges.
2

3. References:-
1) Bridge Engineering by S. P. Bindra, Dhanpat Rai Publication.
2) Indian Road Congress, IRC handbooks ,International Code Council International
Code Council.
3) Traffic and Highway Engineering by J. Garber and L. A. Hoel, Thomson
Learning, Inc.
4) Highway engineering by Khanna & Justo, Nem Chand & Bros. Pub.

4. Bridge :
The drainage structure which facilitates a communication route for carrying road or
railway traffic across an obstruction or depression with or without water is called a
bridge.
Bridge Engineering:
The branch of civil engineering which deals with the design, construction and
maintenance of bridge is called Bridge Engineering.
Major Bridge: Total length varying from 30m to 120m.
Minor Bridge: Total length less than 30m.

5. Culvert: The bridge having total length 6m or less is called a culvert.
Linear Water ways: The length available between extreme edges of water surface at
the highest flood level, measured at right angles to the abutment faces of a bridge is
called as linear waterways.
Afflux: The heading up of the water above its normal level while passing under the
bridge is called afflux.
Abutments: The end support of a bridge superstructure are termed as abutment.
Wing Wall: The wall constructed on both sides of abutment to retain the earth banks
of the river or of the bridge approaches are called wing wall.
Piers: The intermediate support of a bridge superstructure are known as piers.

6. Bridge:
Bridges can be classified into various types based on the following factors:
1) Materials : RCC Bridge, Masonry Bridge, Steel Bridge, Timber Bridge, Pre-
Stressed Concrete Bridge.
2) Floor : Deck Type, Thorough Bridge.
3) Purpose : Highway Bridge, Railway Bridge, Aqueduct.
4) Superstructure : Portal Frame, Balanced Cantilever Bridge, Suspension Bridge.
5) Flood Level : Submersible Bridge
6) Span Length : Culvert, Minor, & Major bridges.
7) Fixed or Movable : Swinging Bridge, Bascule Bridge & Lift Bridge.

7. Culverts:
1) Arch Culvert.
2) Slab Culvert.
3) Pipe Culvert.
4) Box Culvert.

11. Pre-stressed Concrete Bridge:
1) The bridge having their superstructure consisting of pre-stressed concrete
members in any structural form, which support the bridge floor are known as
pre-stressed concrete bridge.
2) The art of pre-stressing consists of inducing compressive stresses in the tensile
zones of the members. The aim of pre-stressing the members is to avoid cracking
of concrete due to principal tensile stresses under severe loads.
3) The technique of pre-stressing checks the tendency of cracking and increase the
shearing capacity of the ordinary reinforced concrete.
4) This enables the use of thinner webs, thereby resulting saving in material, dead
load and ultimately economy in the design of the bridge.
5) Thus the application of the concept of pre-stressing to structural concrete
members has enlarged the span range of concrete bridges.

12. Pre-stressed Concrete Bridge: Advantages & Disadvantages
1) Higher load carrying capacity
2) Reduced deflection of girders
3) Fewer expansion of joints
4) More aesthetic appearance
5) More effective use of precast members
6) Maintenance cost is less
7) More smooth deck and high speed driving
8) Careful supervision
9) Special equipment for construction
10) High tensile steel required which is more costly than ordinarily mild steel

13. Movable Bridge:
Movable spans of bridge are sometimes used over the navigable channels where
permanent and sufficient clear waterway can not be provided. They are needed in
order to provide a passage for the masted vessels or steamers when the bridge is to be
across a navigable river or dock.
1) Swing Bridge consists of balanced girders swinging round a quadrant of a circle
over a pier or a pivot or on a turn table.
2) Bascule Bridge can be raised slightly to permit the passage of numerous small
boats which fail to clear the closed span by a small origin. They revolve about a
horizontal axis and in a vertical position and when lifted attain an upright
position.
3) Traverser Bridge can be rolled backwards and forwards across the opening.
They are provided with rollers on the shore which helps in rolling it off its
position along the approach.

14. Movable Bridge:
Movable spans of bridge are sometimes used over the navigable channels where
permanent and sufficient clear waterway can not be provided. They are needed in
order to provide a passage for the masted vessels or steamers when the bridge is to be
across a navigable river or dock.
4) Transporter Bridge consists of a cradle which moves under an overhead bridge.
The overhead bridge is spanned on high towers provided on each bank.
5) Lift Bridge : The vertical lift bridge have proved to be more economical both in
construction and operation than swing and bascule bridge.

15. Suspension Bridge:
1) Used in places where it is difficult to adopt other types of bridges.
2) They are economically used even for every large spans.
3) Generally they are single span bridge.
4) There are two main cables on each side of the roadways.
5) They are carried over solid piers and are securely anchored to the banks.
6) The roadways is suspended from two main cables by means of suspenders.
7) The cables are carried over the saddle provided on the pier top. The saddles are
either bolted to piers or they rest on rollers to allow for longitudinal movement
resulting from any alternation in cable length.

16. Through Bridge:
1) The bridge having its floor supported or suspended at the bottom of the
superstructure is known as through bridge.
2) This bridge is constructed when the vertical distance between the HFL and the
ground level of approaches is not sufficient to accommodate the superstructure
with a suitable free board.

17. Deck Bridge:
1) The bridge having its floor supported at the top of superstructure is called a deck
bridge.
2) Constructed where the vertical distance between the HFL and ground level of the
approaches is sufficient to accommodate the superstructre with a suitable free
board.

18. Return Walls & Wing Walls:
1) Normally an abutment has one front wall on which the deck or girder of the
bridge is supported and side walls perpendicular to front wall which are also
known as return walls when they are parallel to the bridge and wing walls when
they are curved in plan or at any other angle.
2) The design of wing walls is independent. For straight wing walls it may be
assumed that the equilibrium of each of their cross sections is comparable with
that of an imaginary horizontal wall of indefinite length of the same cross section
holding up an embankment.
3) Generally the wing wall have steadily decreasing cross sections.
4) Their mean thickness at any given section is one third of their height.
5) The design of the wing walls mainly depends upon the nature of the soil in the
embankment.

19. Factors Governing Choice of Type of Bridge :
1) The nature of the river & its bed soil and Physical features of the site.
2) Availability of materials, workers & funds.
3) Volume and the nature of the traffic.
4) Time limit within which the bridge is required to be completed.
5) Whether navigation is done in the river or not.
6) Economic span length of the bridge.
7) Facilities available during construction.
8) Facilities available for maintenance.
9) Foundation Condition.
10) Climatic & Strategic Condition
11) Hydraulic Data and Live loads on the bridge.
12) Length & width of the bridge

20. Points to be Considered for Selection of a Bridge Site:
1) Suitable bearing strata in the stream at a short depth may be available and it
should be geologically suitable.
2) The stream at bridge site should be narrow and straight reach.
3) The site should have firm, straight and high banks.
4) The flow of water at site should be steady and free from whirls and cross
currents.
5) Easy availability of labor, materials and transport facility nearing site.
6) The bridge should not be on the curve and it should be suitable for navigation
purpose.

21. Bridge Numbering :
The numbers are given in the form of fraction, the numerator denoting the number of
kilometers in which the structure is situated and the denominator the kilometer-wise
serial number of the structure.

22. Data to be Collected for Selection of a Bridge Site:
1) Traffic Data
2) Hydraulic data based on stream characteristics
3) Geological Data
4) Climatic Data
5) Catchment Area & Runoff
6) Alignment Data
7) Superstructure Data
8) Foundation Data
9) Availability of Electric Power, Labor, Materials and Transport Facilities, etc.

23. Design Data for Major Bridges:
1) General Data: Road type, BM, Season & its duration, alternative arrangement
2) Catchment area & runoff:
3) Nature of stream: Types of stream, water level,
4) Alignment & Approaches: Right & left Approach, Bridge visibility.
5) Superstructure: Clear roadway over bridge, footpath
6) Foundation Data: Type of foundation and suitability.
7) Existing Structure: Details of existing bridge.
8) Other: Locality, Facility Nearby, etc.

24. Wind Load:
Wind load forces should be considered to act horizontally and in such a direction that
the resultant stresses in the member under consideration are the maximum. It may be
assumed as a horizontal force which act on an area calculated as follows:
For deck structure: The area of the structure as seen in elevation including the floor
system and railings.
For a through a half through structure: The area of the elevation of windward
traces as specified in plus half the area of elevation above the deck level of all others
truss or girders.

25. Live Load:
Road Bridges must be designated to support safety all vehicles that might pass over it
in its life time. To ensure the safety of structure, some form of control must be
maintained and provision must be made for sufficient strength to carry present and
predicted future loads.

26. IRC has evolved suitable loading standards for bridge commensurate with traffic
needs to Indian Highway System. They are of two types:
1. IRC Standards Loading: It consists of uniformly distributed load of 1.13 tones
/ linear meter of each traffic lane plus a knife edge load of 6 tones for computing
bending moment and 9 tones for computing shear force.
2. IRC Heavy Loading: The difference is that the uniformly distributed load was
increased by 0.8 tone/m and knife load was increased by 1 tones each.
The present IRC bridge loadings are of the following three types:
A. IRC class ‘AA’ loading
B. IRC class ‘A’ loading
C. IRC class ‘B’ loading

27. IRC Class AA Loading:
1) This class of loading corresponds to the class 70 loading and is based on the
original classification methods of the defense authorities.
2) Class 70 R and class AA loadings specify a 70 tons tracked vehicle with only
sight differences in the length of the loaded area.
3) Although the vehicles are identical with the same total load, the minimum
spacing between vehicles specified for the two load classes are very different.
4) For 70 R, it is 30m and for class AA it is 90m.
5) This loading is adopted for design of bridge within certain specified areas and
along national highways and SH.

28. IRC Class A Loading:
1) This type of IRC bridge loading was proposed with the object of covering the
worst combination of axel loads and axel spacing, likely to arise from the various
types of vehicles that are normally expected to use the road.
2) The load train according to this type of IRC loading has been arrived at after an
exhaustive analysis of all lorries in all the countries of the world.
3) The load train is composed of a driving vehicle and two tralers of specified axel
spacing and loads.
4) This loading is normally adopted on all roads on which permanent bridge and
culvert are constructed.

29. IRC Class B Loading:
1) This type of IRC bridge loading is similar to class A train or vehicles with
reduced axel load and type contact dimension.
2) This loading is normally adopted for temporary structure and for bridges in
specified areas.

30. Characteristics of Loading:
1) Class TOR and class AA loading specify 70 tones tracked vehicles with only slight difference
in the length of the loaded area.
2) Minimum spacing between vehicles for class TOR is 30m and for class AA is 90m.
3) IRC class AA loading corresponds to class TO loading. This loading is to be adopted for
design of bridges within certain municipal limits in certain existing or contemplated
industrial area.
4) Bridge design for class AA loading should be checked for class A loadings also, as under
certain conditions heavier stress may be obtained under class A loadings.
5) IRC class A loading consider the worst combination of axel loads and axle spacing likely to
arise from various types vehicles that are normally expected to use the roads.
6) IRC class A loading is to be adopted on all roads on which permanent bridge and culvert are
constructed.
7) IRC class B loading is similar to class A train of vehicles with reduced axel loads and tyre
contact dimensions.
8) IRC class B loading is normally to be adopted for temporary structure and for bridge.

31. Force Due To Water Current:
1) The bridge should be designated to withstand water pressure which may cause
the pier to slide or overturn.
2) Scour around the pier due to water current should be taken care of in bridge
design. The stream velocities due to water current which gives horizontal
pressure are to be noted. Hence the bridge is to be designated to sustain this
horizontal pressure.
Earth Pressure for Bridge:
1) Earth Pressure in a bridge is general from back fill. IRC recommends Columb’s
theory of earth pressure with the modification that the height of center of
pressure above bottom as 0.42 of the height of wall above the base instead of
0.33 of that height.
2) A bridge structure should not however designated to withstand a horizontal less
than that exerted by a fluid weighing 480 kg/m3.

32. Seismic Force for Bridge:
1) Seismic failure was not caused by the collapse of any element of the
superstructure but rather by the superstructure shaking off the bearings and
falling to the ground and the structural failure of the loss of the strength of the
soil under the substructure as a result of the vibrations induced in the ground.
2) The influence of seismic forces on a structure depends on the bridge’s elastic
characteristics and the distribution of weight
3) The seismic force should be taken as a horizontal force equal to the appropriate
fraction of the weight of the dead and live load acting above the section under
consideration. Parts of the structure embedded is soil should not be considered to
produce any horizontal forces.

33. Scour Depth:
The process of cutting or deepening of river bed due to action of water is called
scouring. It differs from erosion which causes horizontal widening of the river.

34. Que.1. A bridge is proposed to be constructed across an alluvial stream carrying
discharge of 300 m3/s. Determine the maximum scour depth when the bridge
consists of two spans of 40 meters each. Assume silt factors as 1.05.
Discharge, Q=300m3/s
Silt Factor, f = 1.05
Two span of 40m each, L = 2 x 40 = 80m
Regime surface width W of the stream can be calculated by using the relation,
W = 4.8 x ( Q )1/2 = 4.8 x (300) ½ = 83.14 m.
Regime depth, D = 0.473 (Q/f)1/3 = 0.473 (300/1.05)1/3 = 3.12m
Normal scour Depth, D’ = D (W/L)0.61 = 3.12 (83.14/80)0.61 = 3.19m
Maximum Scour Depth = 2 x D’ = 2 x 3.119 = 6.39

35. Que.2. A bridge is proposed to be constructed across an alluvial stream carrying
discharge of 250 m3/s. Determine the maximum scour depth when the bridge
consists of four spans of 20 meters each. Assume silt factors as 1.0.
Note:
When L < W then the waterway is contracted.
In case of contraction, scour depth is to evaluate by = D (W/L) 1.56
Max. Scour depth = 2 x D’
Maximum of above two will be taken as max. scour depth.

36. Que.3. A flood discharge under a bridge 4764 m3/s. if the normal width and
waterway are 954m and 900m respectively, determine scour depth and afflux.
Silt factor is 1.5 and bridge site is on straight reach.
Regime Depth, D = 6.95m
Normal Scour Depth, D1 = 7.2m
Max Scour Depth, = 14.4m.
Scour depth in case of contraction = 7.61m

37. Que. 4. Calculate the flood discharge from a catchment of 65 sq.m. when the
rainfall during the storm was 15 cm in two hours. The time of concentration is
20 hours and the runoff coeff. For the catchment is 0.35. Assume any other data
required suitably.
Catchment Area = 65 sqm = 0.0065 Hectars
Rainfall during storm, F = 15cm
Time of concentration, Tc = 20 hours
Storm Duration, T = 2 Hours
Runoff Coeff., P= 0.35
Assume f = 0.89
One hr Rainfall Intensity, Io = ((T+1)F)/2 x T = ((2+1)15)/2x2 =11.25cm/hr
Intensity of Rainfall, Ic = Io (2/(Tc+1) = 11.25(2/(20+1) = 1.07 cm/hr
Peak Discharge, Q = 100 x p x f x A x Ic = 100 x 0.35 x 0.89 x 0.0065 x 1.07
Q = 0.217 cumec/hr

38. Afflux:
1) It is the rise in the level of the water surface of a water course above the normal
on the upstream side of a bridge.
2) This rise is due to the obstruction caused by the bridge abutments and piers in the
flow of the water.
3) Afflux is taken as the difference of levels of the downstream and upstream water
surface of the bridge.
4) The natural water way of the rivers or streams is usually greater than the water
way below the bridge, which causes afflux.

39. Que.5. A bridge has a linear waterway of 120m constructed across a stream whose
natural linear waterways is 200 m. If the average flood discharge is 1050 m3/s and
average flood depth is 3m, calculate the afflux under bridge?
Linear Waterways = 120m
Natural Waterway = 200m
Average flood discharge , Q = 1050 m3/s
Average depth of flood = 3m
Unobstructed sectional area of river , A = 20 x 3 = 600 m2
Average velocity prior to obstruction m/sec = V = (Q/A) = 1050 / 600 = 1.75 m/s
Sectional area of river in m2 considering obstruction, A1 = 120 x 3 = 360 m2
Afflux (h1) = ( ( ( V2 ) / 17.88 ) + 0.015 ) x ( ( ( A / A1 )2 - 1 ) )
Afflux (h1) = ( ( ( 1.752 ) / 17.88 ) + 0.015 ) x ( ( (600 / 360)2 - 1 ) )
Afflux, h1 = 0.33m

40. Economic Span of a Bridge:
The economic span of a bridge is the one which reduces the overall cost of a bridge to
be a minimum.
Most economic span length is that which satisfies the following:
1) The bridge has equal span lengths.
2) Cost of supporting structure of superstructure varies as the square of span length.
3) Cost of flooring and parapets varies directly as the span.
4) Cost of one pier and its foundation is constant.
5) Cost of abutments and their foundation is also constant.
Economic Span, l = k √ ( P )
K is constant
P = cost of one pier with foundation.

41. Limitations in adoption of Economic Span of a Bridge:
Adoption of economic span is unsuitable under the following conditions:
1) The suitable foundation for piers is not available at the locations, where piers
come in consideration of economic span.
2) The economic span is more than a particular value which is difficult to erect due
to increased dead load.
3) The section of pier increases substantially, if the span is increased beyond a
certain value.

42. Questions Bank:
1) Discuss deck, through and semi-through types of bridge with neat sketch?
2) Explain the various types of piers with neat sketch?
3) What is bridge superstructure? What are its types?
4) The average width of a stream is 30m and its average depth is 1.5m. The mean
velocity of flow is 1.2m/s. A bridge consisting of 6 m is to be constructed across
the stream. Determine the height of afflux and velocity under the bridge.
5) A bridge is proposed to be constructed across an alluvial stream carrying a
discharge of 300m3/s. Assuming the value of slit factor = 1.1, determine the
maximum scour depth when the bridge consist of (1) two span of 35 m each.
(2) Three spans of 30m each.
6) Write a short note on Afflux, Arch Bridge, Economic Span, cantilever bridge &
flood estimation.
7) Explain different types of wingwall?