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Classification of bridges by superstructure and span; sketch

Short answer

Bridges are classified by superstructure as slab, girder, truss, arch, cable-stayed, suspension, and rigid frame/box culvert. By span length, culvert up to 6 m, minor bridge 6–60 m, major bridge above 60 m, long-span above about 120 m. A sketch shows deck, girders, bearings, piers, abutments, wing walls, foundations, kerbs, footpath, railings, HFL and scour levels.

Classify the bridges according to types of super structure and span length. Make a sketch of a bridge section (longitudinal and cross) and plan indicating its elements.

Classification by superstructure (type of structure)

TypeDescription
Slab bridgeRCC slab spans, up to about 10 m
Girder bridgeRCC T-beam girders with deck slab up to about 25 m; PSC/steel girders up to about 40 m; more with PSC box girders
Truss bridgeTriangulated steel members, 40–100 m or more
Arch bridgeMasonry/RCC/steel arch that carries the load mainly in compression
Cable-stayedDeck supported by inclined cables from towers, about 100–1000 m
SuspensionDeck hung from main cables over towers; the longest spans (above about 500 m)
Rigid frame/box culvertDeck and piers/walls cast monolithically as a frame

Classification by span length (IRC / DoR practice)

  • Culvert: total length up to 6 m (IRC definition).
  • Minor bridge: total length from 6 m to 60 m.
  • Major bridge: total length above 60 m.
  • Long-span bridge: individual spans above about 120 m.
  • Some textbooks instead take minor bridges as about 8–30 m and major bridges as above 30 m.

Sketch of bridge sections and plan

 LONGITUDINAL SECTION
       Deck slab + wearing coat       Railing
  ___________________________________  ___
 |==================================|
  Abutment  Bearing  Girder  Pier   Abutment
  |  |       ^   ^                  |  |
  Wing   HFL ~~~~~~~~~~~~~~~~~~~~~~~~  Wing
 wall    Foundation level below scour
 CROSS SECTION
  Kerb  Carriageway  Kerb  Footpath
 |_|______________|__|_|
   ===== deck slab ======
    [girder] [girder] [girder]
 PLAN
 ----------------------------------
  W.wall |  carriageway          | W.wall
 ----------------------------------

Elements shown: deck slab, girders, bearings, piers, abutments, wing walls, foundations, kerbs, footpath, railings, and the HFL and scour levels. Approach slabs are placed behind each abutment, at the ends of the deck.

✓ Answer checked by Claude Opus 5.5 (high effort)

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