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General design requirements

Selection of Bridge Type
For the selection of bridge type for any site, following are the governing factor:

  • Technical
    All other factors are important but technical aspects play key role. It deals with span of bridge, sizing of cross-section, height, discharge, straight reach of the river etc.
  • Economical
    It is the cost factor, which is directly related to availability of fund and financial resources and the expenses involved in the construction of bridge.
  • Environmental
    Environmental factors are related to the impact of the structure on the environment during and after construction.
  • Aesthetical
    Aesthetic factor is related to the quality of beauty and functionality of bridge structure.

Based Upon Span Ranges Bridge Types are Selected as per Following
S.N. Types Span (in m)

  1. R. C. Slab 6-10
  2. R.C. T – Girder 10-30
  3. Composite 25-40
  4. R.C. Box 30-50
  5. Pre-stressed Concrete Box 40-80
  6. Arch
  7. Masonry 15-30
  8. Concrete 40-70
  9. Steel 50-100
  10. Cable stayed 100-200
  11. Suspension 300-2000
    • Truss 25-300

Essential Design Data and Their Acquisition
The design data essential for bridge design are:

  • Name of the stream, road and identification mark allotted to the crossing and location in km to Centre of crossing.
  • Present and anticipated future volume and nature of traffic on the road at the bridge site.
  • HFL, LWL (low water level), high flood dis-charge, velocity of stream etc.
  • Navigational requirement if any.
  • Cross section and profile of bridge site with topography map covering 100m d/s and 100m u/s.
  • Type of soil, cohesive property, bearing capacity by soil test.

General Design Requirement
Studies to be carried out for the acquisition of basic design data.

  1. Traffic Study
    Data to be acquired
    • Traffic intensity
    • Type of vehicle
    • Pedestrian traffic
    • Utility services to be served
    • Navigational traffic
      Data required for
      • Bridge loading
      • Bridge width
      • Horizontal and vertical clearances
      • Width of footway
  2. Hydrological Study
    Data to be acquired
    • Flood type
    • Water current
    • Design discharge
    • Flood level
    • Scouring depth
    • Linear water way
      Data required for
      • Length of bridge
      • Height of bridge
      • River training works
      • Type and depth of foundation
  3. Geological & Geotechnical Study
    Data to be acquired
    • Engineering properties of soil
    • Geological feature of subsoil
      Data required for
      • Location of bridge
      • Location of pier and abutment
      • Depth and type of foundation
  4. Topographic Study
    Data to be acquired
    • Topographic feature of bridge site
    • Cross section of river profile
    • Longitudinal section of river profile
      Data required for
      • Location of bridge
      • Length of bridge
      • Height of bridge
      • Type of pier and abutment




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