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1. Low Cost Bridges

2.  Low cost bridges may be defined as bridges constructed and
maintained at low cost.
 Necessity
1. Lack of resources, time, money and skill
2. Repairs to permanent works
3. To facilitate the execution of permanent works
4. Temporary need
5. Undertaking project surveys in the interiors
 Constructed using locally available materials like stone, bricks
and timber
 Causeway: A road causeway is a pucca dip which allows floods
to pass over it.

3.  Known as Irish bridge

4.  On river which remains dry for most times

5.  Involves heavy earthwork – should with easy slope

6.  Road with stone or brick paving
 Cut off wall (Dwarf wall) – To prevent scour and undermining
 Cut off wall 60 cm deep on u/s and 120 to 150 cm on d/s
 For steep slope – Road at higher level with masonry wall at
each end

8.  It is submersible road bridge
 Having sufficient number of opening
 Opening –with abutments, piers, floors, slabs and arches
 Approaches with slope 1 in 20

9.  Apron of Concrete or Masonry - velocity is high and stream
bed is soft
 Road – CC slab or stone blocks set in mortar

11.  Bed level causeway
Provided where interruption to traffic less than 24 hour
Generally 12 to 25 cm above bed
 For sound and economic design
Afflux
Scour on u/s and d/s
Upstream pressure
 Factors considered to upgrade existing causeway to high level
bridge
Number of interruptions
Duration of interruptions
Type of flow
Type and amount of traffic
Importance of road

12.  Culvert : A culvert is a small bridge for carrying water
beneath a road or railway.
 Road culvert – span limited to 5 m
 Railway culvert – span limited to 6 m
 Types of culverts:
1. Arch culvert
2. Slab culvert
3. Pipe culvert
4. Box culvert

13.  Consists of abutments, wing walls, arches, parapets and the
foundations.
 Constructed – Brickwork or Concrete
 Floor and curtain wall – velocity of flow and nature of soil

15.  Consists of RCC slab with or without beams or a stone slab,
with or without steel girder
 Deck slab – one way slab
 Design – One lane of IRC class AA track vehicle or one lane
of IRC class AA wheeled loading or two lanes of class A
loading

17.  Provided – discharge is small and sufficient headway is not
available
 Pipes –diameter not less than 60 cm
 No. and dia. Of pipes – discharge and height of bank
 Concrete bedding
 Gradient – not less than 1 in 1000

18.  Consists of one or more no. of rectangular or square openings
 Provided – soil is soft and load to be spread over wide area
 RCC box culvert – abutments, top and bottom slabs cast
monolithically
 Height of vent – rarely exceed 3 m

19.  For single span up to 3 m and double span up to 6 m

20.  Height of box – at road level or at depth below road
level

21.  Splayed wing wall at 450 – retain earthwork, guide
water flow