Guidelines

For Bridges and Culverts

General

• Frequency of roads and bridges varies depending upon region and terrain.

• Number of culverts in a km of length can be 1-3 in undulating region.

• 1 small bridge can be in 1-4km length of road.• Number of culverts can be increase in

hilly/undulating region.

Dimensions

• Culverts- A cross drainage structures having length up to 6m.

• Bridges- A structure have length above 6m.• Minor Bridge- Having length between 6m-60m.• Major Bridges- Having length 60m and above.• Small Bridge- overall length of structure 30m.

And an individual span should not be more than 10m.

Clear Span & Effective Span

• Clear Span- The distance between the inside surfaces of the two supports of a structural member.

• Effective Span- The center-to-center distance between the supports of abeam, girder, or other structural member.

Nomenclature• The value of design span, clear span, effective

span and end to end deck for which standard designs available are-

• All these spans will have tar paper bearings.Clear Span Effective Span End to end of deck2.6 3 6.43.6 4 4.44.6 5 5.45.6 6 6.46.6 7 7.47.6 8 8.48.6 9 9.49.6 10 10.4

RCC BOXES

• Single cell-• Culvert: 2mx2m, 5mx3m, 5mx4m, 2mx3m,

3mx3m, 4mx4m, 4mx5m• Small Bridges-6mx3m, 6mx4m, 6mx5m,

6mx6m, 7mx5m, 8mx5m, 8mx6m, 8mx7m

• Double Cell-• Culverts: 2mx2m, 2mx3m• Small Bridges: 3mx2m, 3mx3m

• Triple Cell• Small Bridges: 2mx2m, 3mx3m

• These are designed for varying bearing capacity of foundation stratum up to 20t/m2

• More than this higher designs must be preferred.

• Length Related to Catchment Area- I s is found that when catchment area is up to 1sq.km a culvert is required and for more than 1sq.km a small bridge will be necessary.