50 Important Definitions in Bridge Engineering

Bridge Engineering

1. Bridge : Bridge is a structure having a total length of above 6 m between the inner faces of the dirt walls for carrying traffic or other moving loads over a depression or obstruction such as channel, road or railway. These bridges are classified as :

• Small bridge – Overall length of the bridge between the inner faces of dirt walls is up to 30m and where individual span is not more than 10m
• Minor bridge – Total length up to 60m
• Major bridge – Total length greater than 60m

2. Culvert : A cross drainage structure having total length of 6 m or less between inner faces of dirt wall.
3. Foot Bridge : A bridge extensively used for carrying pedestrians, cycles and animals.
4. High Level Bridge : A bridge, which carries the roadway above H.F.L. of the channel.
5. Submersible Bridge/Vented Causeway : A bridge designed to be over-topped during floods.
6. Channel : A natural or artificial watercourse.
7. Clearance : The shortest distance between boundaries at a specified position of bridge structure.
8. Freeboard : The difference between H.F.L. (allowing afflux) and foundation level of road embankment on approaches.
9. H.F.L. : Highest flood level is the level of highest flood ever recorded or the calculated level for design discharge.
10. L.W.L. : Lowest flood level is the level of the water surface obtained in dry season.
11. Length of Bridge : The length of a bridge structure will be taken as overall length measured along the center line of the bridge between inner faces of dirt wall.
12. Linear Waterway : Width of waterway between the extreme edges of water surface at H.F.L. measured at right angles to the abutment face.
13. Effective Linear : The total width of the waterway of the bridge at H.F.L. minus Waterway effective width of obstruction.
14. Safety Kerb : A roadway kerb for occasional use of pedestrian traffic.
15. Width of Carriageway: Minimum clear width measured at right angles to the longitudinal centre line of bridge between inside faces of roadway kerb or wheel grades.
16. Super elevation/Cant/Banking : The transverse inclination given to the c/s of a carriageway on a  horizontal curve in order to reduce the effects of centrifugal force on a moving vehicle.
17. Vertical clearance : The height from the design highest flood level with afflux of the channel to the lowest point of the bridge superstructure at the position along the bridge where clearance is denoted.

18. Bearings : The part of the bridge structure which bears directly all the forces from the structure above and transmits the same to the supporting structure.
19. Sliding Bearings : A type of bearing where sliding movement is permitted.
20. Rocker Bearing : No sliding movement is permitted but which allows rotational movement.
21. Sliding cum rocker Bearing: A type of bearing which in addition to the sliding movement either  the top or bottom plate is provided with suitable curvature to permit rotation.
22. Roller cum Rocker Bearing : A type of bearing, which permits longitudinal movement by rolling and simultaneously allows rotational movement.
23. Elastomeric Bearing : A bearing consisting of one or more internal layers of elastomer boarded to internal steel laminates by the process of vulcanisation. The bearing cateress for translation and/or rotation of the superstructure by elastic deformation.
24. Laminated Bearing :
A bearing composed of alternate layer of elastomer and laminates integrally bonded during vulcanisation.
25. Fixed POT Bearing : A type of POT bearing which along with vertical load bears and transmits horizontal force in any director and allows rotation about any axis in horizontal plane without permitting any movement in horizontal plane.
26. True sliding type POT-cum-PTFE Bearing : A type of POT bearing which bears and transmit vertical load and  allows movement in any direction in the horizontal plane and accommodates rotation about any axis in horizontal plane.
27. Guided Sliding type POT cum PTFE Bearings : A type of POT bearing which along with vertical load bears and transmits horizontal force in one direction only and allows movement perpendicular to that direction and allows rotation about any axis in horizontal plane.
28. Free PTFE Sliding Assembly : A type of PTFE sliding assembly, which along with vertical load bears and transmits horizontal force in one direction and allows movement perpendicular to that direction.
29. Guided PTFE Sliding Assembly : A type of PTFE sliding assembly, which along with vertical load bears and transmits horizontal force in one direction and allows movement perpendicular to that direction.
30. Pin Bearing : A bearing consisting of a metal pin provided within a metal cylinder to bear and transmit horizontal free along any direction in the horizontal plane and accommodating rotational movement about any axis. Pin bearing cannot bear or transmit any vertical load.
31. Metallic Guide Bearing : A bearing consisting of a sliding assembly with restraint along a desired direction to bear and transmit horizontal force and capable of allowing movement in a direction and to the direction of horizontal force. Metallic Guide Bearings and capable of allowing rotation only about an axis perpendicular to the plane of sliding. Metallic Bearing cannot bear or transmit any vertical load.
32. Abutment : The end supports of deck of bridge, which also retains earth, fill of approaches behind fully or partly.
33. Box type Abutment and Return Wall : When the return walls on two sides are integrated with abutment and a back wall parallel to abutment is provided end of the returns with or without additional internal wall along or across length, this structure is called box type abutment and return wall or end block.
34. Spill through Abutment: An abutment where soil is allowed to spill through gaps along the length of abutment such as column structure where columns are placed below deck beams and gap in between is free to spill earth.
35. Afflux : The rise in the flood level of the river immediately on the upstream of a bridge as a result of obstruction to natural flow caused by the construction of bridge and its approaches.
36. Bearing Capacity : The supporting power of a soil / rock expressed as bearing stress is referred to as its bearing capacity.
37. Safe Bearing Capacity : The maximum pressure which the soil can carry safely without  risk of shear failure and it is equal to the net Safe Bearing Capacity plus original overburden pressure.
38. Cofferdam : A structure temporary built for the purpose of excluding water or soil sufficiently to permit construction or proceed without excessive pumping and to support the surrounding ground.
39. Foundation : The part of bridge in direct contact with and transmitting load to the founding strata.
40. Pier : Intermediate supports of the superstructure of a bridge.
41. Abutment Pier : It is designed for a condition that even if one side arch span collapses it would be safe. Generally provided after 3 or 5 spans in multiple span arch bridges.
42. Retaining Wall : A wall designed to resist the pressure of earth filling behind.
43. Return Wall : A wall adjacent to abutment generally parallel to road or flared up to increase width and raised up to the top of road.
44. Toe wall : A wall built at the end of the slope of earthen embankment to prevent slipping of earth and / or pitching on embankment.
45. Wing Wall : A wall adjacent to abutment with its top up to R.T.L. near abutment and sloping down up to ground level or a little above at the other end. This is generally at 45 degrees to the alignment of road or parallel to the river and follows the profile of earthen banks.
46. Substructure : The bridge structure such as pier and abutment above the foundation and supporting the superstructure. It shall include returns and wing walls but exclude bearings.
47. Well foundations : A type of foundation where a part of the structure is hollow, which is generally built in parts and sunk through ground or water to the prescribed depth by removing earth through dredge hole.
48. Tilt of Well : The inclination of the axis of the well from the vertical expressed as the tangent of the angle between the axis of the well and the vertical.
49. Shift of Well : The horizontal displacement of the center of the well at its base in its final position from its designed position.
50. Skew angle of Bridge : It is the angle between the perpendicular to the flow of traffic direction and the flow direction of river.