1.5 class a,b
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This document discusses structural design considerations for bridges and culverts. It covers types of bridges selected based on span length and economics. It also discusses loads on bridges including dead load, live load, impact load, wind load, and other factors. The document provides details on solid slab bridges, girder bridges, and truss bridges. It also covers design of box culverts.
1.5 class a,b
- 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
- 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
- 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
- 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.
- 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).
- 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