BRIDGE & ITS COMPONENTS
BRIDGE : A structure facilitating a communication route for carrying road traffic or other moving loads over a depression or obstruction such as river, stream, channel, road or railway. The communication route may be a railway track, a tramway, a roadway, a footpath, a cycle track or a combination of them.
COMPONENTS OF A BRIDGE : Broadly a bridge can be divided into two major parts :
1) Superstructure
2) Substructure
SUPERSTRUCTURE : The superstructure of a bridge consists of structural members carrying a communication route. Thus, handrails, guard stones and flooring supported by any structural system such as beams, girders, arches and cables above the level of bearings constitute the superstructure.
SUBSTRUCTURE : Substructure is a supporting system for superstructure. It consists of the following :
1) abutments
2) piers and abutment piers
3) wing walls
4) foundation for the piers and abutments
OTHERS : The other main parts of a bridge structure are approaches, bearings, and river training works, like aprons, revetment for slopes at abutments, etc.
IMPORTANT TERMS USED IN BRIDGE ENGINEERING :
The following definitions of certain important terms used in bridge engineering are given below :
1) BRIDGE : A structure facilitating a communication route for carrying road traffic or other moving loads over a depression or obstruction.
2) HIGH LEVEL BRIDGE or NON- SUBMERSIBLE BRIDGE : The bridge which does not allow the high flood waters to pass over them. All the flood water is allowed to pass through its vents.
In other words, a High level bridge carries the roadway above the highest flood level of the channel.
3) SUBMERSIBLE BRIDGE : A submersible bridge is a structure which allows flood water to pass over bridge submersing the communication route. Its formation level should be fixed so as not to cause interruption to traffic for more than three days at a time nor for more than six times in a year.
4) CAUSEWAY : It is a pucca submersible bridge which allows floods to pass over it. It is provided on less important routes in order to reduce the construction cost of cross drainage structures. It may have vents for low water flow.
5) FOOT BRIDGE : The foot bridge is a bridge exclusively for carrying pedestrians, cycles and animals.
6) CULVERT : When a small stream crosses a road with linear waterway less than about 6 meters, the cross drainage structure so provided is called a culvert.
7) DECK BRIDGES : These are the bridges whose flooring are supported at the top of the superstructures.
8) THROUGH BRIDGES : These are the bridges whose floorings are supported or suspended at the bottom of the superstructure.
9) SEMI THROUGH BRIDGES : These are the bridges whose flooring are supported at some intermediate level of the superstructure.
10) SIMPLE BRIDGES : They include all beam, girder or truss bridges supported at both ends only. It is suitable for spans up to 8 meter.
11) CANTILEVER BRIDGES : Bridges which are more or less fixed at one end and free at the other. It can be used for spans varying from 8 meters to 20 meters.
12) CONTINUOUS BRIDGES : Bridges which continue over two or more spans. They are used for large spans and where unyielding foundations are available.
13) ARCH BRIDGES : These are the bridges which produce inclined pressures on supports under vertical loads. These bridges can be economically used upto spans of about 200 meters. The arches may be in the barrel form or in the forms of ribs.
14) RIGID FRAME BRIDGES : In these bridges, the horizontal deck slab is made monolithic with the vertical abutment walls. These bridges can be used upto spans of 20 metre. Generally this type of bridge is not found economical for spans less than 10 metres.
15) SQUARE BRIDGES : These are the bridges at right angles to the axis of the river.
16) SKEW BRIDGES : The bridges which are not at right angles to the axis of the river.
17) SUSPENSION BRIDGES : These are the bridges suspended on cables anchored at ends.
18) UNDER BRIDGES : It is a bridge constructed to enable a road to pass under another work or obstruction.
19) OVER BRIDGE : It is a bridge constructed to enable one form of land communication over the other.
20) CLASS AA BRIDGE : These are bridges designed for IRC class AA loading and checked a loading.
21) CLASS A BRIDGES : These are the permanent bridges designed for IRC class A loading.
22) CLASS B BRIDGES : These are the temporary bridges designed for I.R.C class B loading.
23) VIADUCT : It is a long continuous structure which carries a road or railway like a bridge over a dry valley composed of spans over trestle bents instead of solid piers.
24) APRON : It is a layer of concrete, masonry stone, etc. placed like flooring at the entrance or outlet of a culvert to prevent scour.
25) CURTAIN WALL : It is a thin wall used as a protection against scouring action of a stream.
26) PIERS : They are the intermediate supports of a bridge superstructure and may be of solid or open type.
27) ABUTMENTS : They are the end supports of the superstructure.
28) EFFECTIVE SPAN : The center to center distance between any two adjacent supports is called the effective span of a bridge.
29) CLEAR SPAN : The clear distance between any two adjacent supports is called clear span.
30) ECONOMIC SPAN : The span, for which the total cost of bridge structure is minimum is known as economic span.
31) AFFLUX : Due to construction of the bridge there is a contraction in waterway. This results in rise of water level above its normal level while passing under the bridge. The rise is known as afflux.
32) FREE BOARD : Free board at any point is the difference between the highest flood level after allowing for afflux, if any, and the formation level of road embankment on the approaches or top level of guide bunds at that point.
33) HEADROOM : Headroom is the vertical distance between the highest point of a vehicle or vessel and the lowest point of any projecting member of a bridge.
34) LENGTH OF THE BRIDGE : The length of a bridge structure will be taken as the overall length measured along the center line of the bridge from end to end of the bridge deck.
35) LINEAR WATERWAY : The linear waterway of a bridge shall be the length available in the bridge between extreme edge of a water surface at the highest flood level, measured at right angles to the abutment faces.
36) EFFECTIVE LINEAR WATERWAY : Effective linear waterway is the total width of waterway of the bridge minus the effective width of obstruction.
37) LOW WATER LEVEL (L.F.L) : The low water level is the level of water surface obtained generally in the dry season.
38) ORDINARY FLOOD LEVEL (O.F.L) : It is the average level of a high flood which is expected to occur normally every year.
39) HIGHEST FLOOD LEVEL (H.F.L) : It is the level of the highest flood ever recorded or the calculated level for the highest possible flood.
