structural design of bridge

1. Structural Design of bridge
and Culvert
SDE. Prabhat Kumar Jha
Department of Road
9841360244

2. Structural design of bridge:
• various types of bridges, selection and type of bridges and
economic span length,
• types of loads, forces and stresses, live load, impact load,
wind load, longitudinal forces, lateral loads, centrifugal
force,
• width of roadway and footway, general design
requirements,requirements,
• solid slab bridges, deck girder bridges, B.M. in slab
supported on four edges, distribution of live loads on
longitudinal beams, method of distribution coefficients,
Courbon’s method,
• design of a T- beam bridge, balanced cantilever bridge,
Design of box culvert

3. What is a bridge?
• A bridge is a structure that spans a divide
such as:
– A stream/river/ravine/valley
– Railroad track/roadway/waterway
• The traffic that uses a bridge may include:
– Pedestrian or cycle traffic
– Vehicular or rail traffic– Vehicular or rail traffic
– Water/gas pipes
– A combination of all the above

4. 700 A.D. Asia700 A.D. AsiaNatural BridgesNatural Bridges
Clapper Bridge
Tree trunk
Stone
History of Bridge DevelopmentHistory of Bridge Development
Great Stone Bridge in China
Low Bridge
Shallow Arch
100 B.C. Romans100 B.C. Romans
Stone
The Arch
Natural
Cement
Roman Arch Bridge
Shallow Arch
1300 A.D. Renaissance1300 A.D. Renaissance
Strength of
Materials
Mathematical
Theories
Development of
Metal

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

6. •Type of Bridge
Based on Materials
RCC Bridge
Prestessed concrete Bridge
Steel Bridge
Timber Bridge
Based on Inter-Span relation
Simply Supported Bridge
Continuous Bridge
Cantilever Bridge
Based on Structural Behavior
RCC T-Girder Bridge (Max. 25m)
Steel Truss Bridge (Max. 30-100m)
Bow String Girder Bridge (Max. 30-35m)
Arch Bridge (Max. 35-200m)
Balanced Cantilever Bridge (Max. 30-60m)
Suspension Bridge (Max. 400-1200m)
Cable Stayed Bridge (Max. 200-600m)
Rigid Frame Bridge (Max. 25m)

7. •Type of Bridge
Based on Function
Aqueduct
Pedestrian Bridge
Road Bridge
Railway Bridge
Pipeline Bridge
Based on Length / Span
Culvert : Length up to 6 m
Minor Bridge : When length ≤ 50 m (with span ≤ 25 m )
Major Bridge : When span >25 m or length >50 m (with smaller spans)
Special Bridge : Bridges that require special design considerations, whose
construction features
(e.g. concrete girder bridges with >50m span, steel trusses >
100m span, arch bridges, suspension bridges, cable-stayed bridges and other
nonstandard
According to the position of the bridge floor relative to the superstructure :
deck, through, half-through etc.
According to method of construction : pin-connected, riveted, welded etc.
bridges).

10. Basic Components of a Bridge
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 ispermanent 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.

11. Basic Components of a Bridge

12. Typical Beam/Girder Bridge

13. A Typical Single Span Bridge

14. • Because the truss is a hollow skeletal
structure, the roadway may pass over or
even through the structure allowing for
clearance below the bridge often not
Truss Bridges
clearance below the bridge often not
possible with other bridge types

15. • Warren Truss
– The Warren truss pattern features a series of isoceles or
equilateral triangles. In contrast to the Pratt and Howe
patterns, the diagonals alternate in direction.
– Warren trusses are typically used in spans of between 150-
Truss Bridges
– Warren trusses are typically used in spans of between 150-
300 feet
– The most common truss. For smaller spans, no vertical
members are used lending the structure a simple look. For
longer spans vertical members are added providing extra
strength

16. Truss Bridges
• Pratt Truss
– The Pratt truss design contains a downward pointing
V in the center with parallel diagonals on each side.
– Except for those diagonal members near the center,
all the diagonal members are subject to tensionall the diagonal members are subject to tension
forces only while the shorter vertical members handle
the compressive forces. This allows for thinner
diagonal members resulting in a more economic
design.

17. • Howe Truss
– The Howe truss pattern features an upward pointing
V formed by the central diagonals with parallel
diagonals on either side. Unlike the Pratt pattern the
diagonals will be in compression when loaded
Truss Bridges
diagonals will be in compression when loaded
– It is the opposite of the Pratt truss. The diagonal
members face in the opposite direction and handle
compressive forces. This makes it very uneconomic
design for steel bridges and is rarely used.

18. • Warren Truss
Build Your Bridge!
• Pratt Truss
• Howe Truss

19. Types of Trusses
K-Truss

20. Whipple Bowstring

21. Types of Trusses
Bollman

22. Cuts
Cross Overs – Each time a line crosses another line you will need to
make a cut – On one line for this bridge a minimum of 12 cuts will
need to be made!

23. Town Lattice

24. Arch Bridges
• Arches used a curved structure
which provides a high
resistance to bending forces.
• Both ends are fixed in the
horizontal direction (no
horizontal movement allowed
in the bearings).in the bearings).
• Arches can only be used
where ground is solid and
stable.
• Hingeless arch is very stiff and
suffers less deflection.
• Two-hinged arch uses hinged
bearings which allow rotation
and most commonly used for
steel arches and very
economical design.
Hinge-less Arch
Two hinged Arch

25. Arch Bridges
• The three-hinged arch
adds an additional hinge at
the top and suffers very
little movement in either
foundation, butfoundation, but
experiences more
deflection. Rarely used.
• The tied arch allows
construction even if the
ground is not solid enough
to deal with horizontal
forces.
Three-hinged Arch
Tied Arch

26. Simple Supported Bridge Arch Bridge
Cable Stayed Bridge
Suspension Bridge
Balanced Cantilever Bridge

27. FACTORS CONSIDERED IN DECIDINGFACTORS CONSIDERED IN DECIDING
BRIDGE TYPEBRIDGE TYPE
••Geometric Conditions of the SiteGeometric Conditions of the Site
••Subsurface Conditions of the SiteSubsurface Conditions of the Site
••Functional RequirementsFunctional Requirements
••AestheticsAesthetics••AestheticsAesthetics
••Economics and Ease of MaintenanceEconomics and Ease of Maintenance
••Construction and Erection ConsiderationConstruction and Erection Consideration
••Legal ConsiderationsLegal Considerations
Selection of Type of Bridge
Principle : The entire completed structure should be the most suitable to carry
the desired traffic , adequate strong to support the incident loads, economical
and aesthetically pleasing.

28. Factors :
1. Hydraulic Factors and River Regime
: Linear Waterway, Scour Depth, x-section at Bridge axis
Ex:- LW > 25m and deep gorge : Steel Truss Bridge or Plate Girder or Arch
Bridge
Ex:- If the scour depth more than 5-7m from Ground Level and Open
Foundation is uneconomical : Steel Truss Bridge
2. Topography and Soil Conditions:
Ex:- Rocky Bank with favorable geological condition may be an ideal site for Arch
Bridge
Ex:- Weak Soil Condition, Simply Supported Bridge rather than Continuous Bridge

29. Factors :
3.A high level structure with uninterrupted traffic as on a National Highway and need
to replace the no. of piers may necessitate a cantilever bridge or a cable stayed
bridge or a series of Simply Supported truss bridge:
4. Large navigational clearances required may dictate the use of particular type such
as Arch Bridge, Cantilever Bridges, cable stayed construction or suspension bridge.
5.The climate and environmental conditions would preclude the use of some type and
require some others.
Ex:- Corrosive Environment , Never Steel BridgeEx:- Corrosive Environment , Never Steel Bridge
6.Shortage of Fund may necessitate the adoption of a submersible bridge instead of
a high level bridge on a road with low volume of traffic.
Ex:- Vented Causeway
7.Type of Traffic restricts choice of type .
Ex:- For Railway most preferred choice is Steel truss Bridge
8.The personal preferences or Company Specialization of designer / construction
firms.
Es:- Hulas always try to design Steel Truss Bridge under Design-Build Contract

30. 9.Availability of Material
Ex:- Remote Hilly region : RCC Bridge truss bridge is last choice.
10.Economy
Cost of Sub-structure more or less equal to Cost of Superstructure

31. •Economic Span of Bridge
Thumb:ForRCCSlabBridge:leconomic=1.5H
ForSteelTrussBridge:Leconomic=3H
Thumb:ForRCCSlabBridge:leconomic=1.5H
ForSteelTrussBridge:Leconomic=3H

32. Choice of Location of Bridge Site
In broader sense, the key factors to be
considered:
1. Hydrological and River Morphological
FactorsFactors
2. Geological and Geotechnical Factors
3. Social and Economic Factors
4. Safety Factors

33. Choice of Location of Bridge Site
A multi disciplinary expert team selects axis based on :-
1. The reach of the river should be straight so min.
disturbance effects on flow due to structures
2. The river in the reach should have a regime flow free of
whirls, eddies and excessive to avoid excessive scour
and construction difficulties
3. The site should have firm high banks that are fairly
inerodable to avoid breaching of the approachesinerodable to avoid breaching of the approaches
4. The site on a meandering river should be a nodal point to
avoid normal shifting of region
5. The approaches for the bank should secure enough to
flash flood / design flood
6. Approaches bank should not be too high or too expensive
to build
7. The site should have reasonable proximity to the main
road.

34. Choice of Location of Bridge Site
8.Site requiring minimum recurring maintenance costs
9.Bridge site and approach slope should be stable and
favorable rock orientation
10.The crossing should provide the shortest possible
line of communication between Demand area and
Supply Area as otherwise its usage will be very muchSupply Area as otherwise its usage will be very much
limited and the intensity of usages will be less.
11.The bridge length should be Shortest and Safe
Practically, the site selection is a matter of judgment.
Various alternatives satisfying many conditions as
possible have to be chosen and put to the economic
test before detailed investigations for a chosen site are
undertaken

35. A Typical Single Span Bridge

36. Typical Beam/Girder Bridge

37. Basic Components of a Bridge

38. Basic Components of a Bridge
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
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.

39. Bridge LoadingsBridge Loadings

40. IRC 6:2014 : Standard Specifications and Code of Practice for
Road Bridge / Section II “Load and Stresses”
Type of Loads
1.Dead Load : of Bridge Components
2.Live Load : Class A, B, AA,
3.Impact Load
4.Wind Load
5.Longitudinal Force
6.Centrifugal Force6.Centrifugal Force
7.Buoyancy Force
8.Water Current Force
9.Thermal Force
10.Deformation Force due to material property change
11.Earth Pressure Load
12.Seismic Force

41. 1.Dead Load : of Bridge Components
Load = Volume x Density
Concrete : 25 KN/sqm
Asphalt : 22 KN/sqm
Steel : 78.50 KN/sqm

42. Live Load : Class A for All permanent Bridge
8 Axles and Total train length = 25m
Mini. Distance between two successive trains = 18.5m

43. Live Load : Class A….

45. Live Load : Class B for temporary Bridge
8 Axles and Total train length = 25m
Mini. Distance between two successive trains =
18.5m

46. Live Load : Class B

47. Live Load : 70R (Wheel) Vehicle
For Slab /
Transverse
Analysis

48. Live Load : 70R (Track) Vehicle
C
=1.2m

57. Wind Load
Dynamic Load but normally approximated to static
load uniformly distributed over the vertical plane /
elevation area
450 kg/sqm
Longitudinal ForceLongitudinal Force
Due to vehicle Braking and Accelerating while passing
the Bridge.
Approximated to 20% of Lane Load applied at 1.2m
above the level of deck
transfer to substructure through bearing

58. Centrifugal Force
For a bridge on horizontal curve, CF developed while vehicle
passing it.
C = Live Load x (Velocity)^2 / (127 x Radius of Curve) at 2m
above the deck Level.
Buoyancy Force
Under water bridge structure can suffer from buoyance force for
very large structure and result in undermining effect.
BF = w x H (Upward)

59. Water Current Force
Horizontal forces are exerted on submerged
part of sub-structures because of water
current, max at top of surface and linearly
reduces to ZERO at bed level.
k = Constant depend on shape of Pier

60. •Type of Loads (IRC 6:2000)
Thermal Force
Tensile forces developed due to temperature fluctuating in temperature at Bearing
LevelLevel
Deformation Force
Due to change in material properties and geometry
: shrinkage, creep

61. Ka Value :
Max. 0.297
Min. 0.266

67. Seismic Force
Vertical Seismic Coefficient = 0.75 x Horizontal Seismic coefficient
Seismic Force is not considered simultaneously with Wind Force

69. Loads
Superstructure
Foundation /
Substructure
For T-Girder
/Box Girder
For Truss For All type
1.Dead Load : of Bridge Components
1.Live Load : Class A, AA, Pedestrian
1.Impact Load
1.Wind Load
1.Longitudinal Force1.Longitudinal Force
1.Centrifugal Force Occasional
1.Buoyancy Force
1.Water Current Force
1.Thermal Force
1.Deformation Force due to material
property change
1.Earth Pressure Load
1.Seismic Force

70. NEPAL BRIDGE STANDARDS-2067
DESIGN DISCHARGE
• All permanent bridges shall be designed
for a discharge of 100 yrs. return period.
For the calculation of design dischargeFor the calculation of design discharge
empirical formulas especially developed
for other catchments shall not be used.

71. NEPAL BRIDGE STANDARDS-2067
4.0 BRIDGE LOADINGS
4.1 ROAD BRIDGE LOADINGS
• All permanent road bridges in Nepal shall
be designed as per IRC loadings orbe designed as per IRC loadings or
AASHTO loadings. All design shall be
carried out in accordance to IRC
standards for bridges unless otherwise
specified in this document.

72. NEPAL BRIDGE STANDARDS-2067
5.0 GEOMETRIC STANDARDS
5.1 CARRIAGEWAY
• All bridges in Highways and Urban Roads shall
be designed with a minimum carriageway widthbe designed with a minimum carriageway width
of 7.5m.
• All bridges in Feeder Roads shall be designed
with a minimum carriageway width of 6.0m.
• No permanent bridge shall be designed with a
carriageway width of less than 6.0m except on
minor (district and village) roads having length
less than 25m.

73. NEPAL BRIDGE STANDARDS-2067
5.2 FOOTPATH
• Footpaths shall be provided on all bridges
located at settlement areas or on areas of high
movement of pedestrian traffic. They should bemovement of pedestrian traffic. They should be
separated from the vehicular traffic by safety
curbs (in rural areas) and by raised footpath or
curbs (in urban areas).The width of the footpath
should be decided according to projection of
pedestrian traffic, however, a minimum clear
width(excluding the width of railings) of 1.0
m footpaths to be provided, where necessary.

74. NEPAL BRIDGE STANDARDS-2067
6.0 CLEARANCES
6.1 VERTICAL CLEARANCE
• The vertical clearance of structures shall be,
• For all roads not less than 4.75 m for through• For all roads not less than 4.75 m for through
structures
• Overhead wires, poles etc shall be at least 7.0 m
above the highest point of the road surface.

75. NEPAL BRIDGE STANDARDS-2067
7.0 BRIDGE CLASSIFICATION
Classification of bridges shall be as follows:
Culvert : Length up to 6 m
Minor Bridge : When length 50 m (with span 25 m )Minor Bridge : When length 50 m (with span 25 m )
Major Bridge : When span >25 m or length >50 m(with
smaller spans)
Special Bridge : Bridges that require special design
considerations, whose construction features(e.g.
concrete girder bridges with >50m span, steel trusses >
100m span, arch bridges, suspension bridges, cable-
stayed bridges and other nonstandard bridges).

76. NEPAL BRIDGE STANDARDS-2067

77. General Design Requirements
•Design Discharge 100yr Return Period
•Linear Waterway
•Bridge Span and Length
•Vertical Clearances
•Max. Scour depth•Max. Scour depth
•Width of Carriageway and Footpath
•Bridge Superstructure Selection
•Geotechnical Investigation
•Bridge Foundation Selection
•Concept of Design : Working Load, Limit State Design