Components Parts of a Bridge
What is Bridge
A structure carrying a road, path, railway etc. across a river, road or other obstacles or you can say that It is a structure that facilitates the crossing over the deep valley full of water or other obstructions etc.
Requirement of an Ideal Bridge
1). It should be economical.
2). It should serve the indented function with safety and convenience.
3). It should give aesthetic elegant look.
Components Parts of a Bridge
Bridge Structure can be divided into two parts:-
i). Super – structure.
ii). Sub – Structure.
i). Super – structure
It is the part of the bridge over which the traffic moves safely.
ii). Sub – Structure
The Sub Structures supports the super structures and distributes the load to the soil below through foundations. Sub – structure consist of foundations, piers, abutments and wing walls.
Main parts of a bridge:-
4). Pile Cap.
7). Concrete Pad.
8). Bearing pad.
11). Road pavement.
12). Rail Track.
There are different types of bridges. Different bridges types contains different parts, Following are the main parts of a bridge:-
A deck is the surface of a bridge to pass vehicles, goods, people etc. from one side to another.
In engineering, Abutments refer to the substructure at the end of a bridge span or dam where the structure & superstructure rest or contracts or you can say that the end supports of the super – structure of a bridge are called abutments.They may be either arched or flat.
a). Abutments Piers
In such bridges, Sometimes some of the intermediate supports are piers are made stronger section than others. They are thus designed to act as an abutment in addition to piers. Abutments are vertical structures used to retain the earth behind the bridge.
A pile bridge is a structure that uses long poles foundations which are made of wood, concrete or steel or which are hammered into the soft soil beneath the bridge until its end reaches a hard layer of compacted soil or rock.
The intermediate supports of the super structure or vertical members of columns upon which the bridge is supported on pier caps are called piers. Bridge pier support the span of the bridge and transfer the loads from super structure to the sub soil through the foundation. Pier should be strong enough to take the both vertical or horizontal load.
Piers Perform two main functions :-
1). Transferring Super-structure vertical loads to the foundation.
2). Resisting to the horizontal forces acting on the bridge.
A girder bridge is that bridge in which girders are used for supporting its deck. The two most common types of modern steel girder bridge are box and plate.
6). Rail Track
Normally road traffic is the main vehicles onto the bridge but if the train needs to be passed through that bridge. Rail track is the extra component.
Some Important definition you must know
i). Valley :-
A depression in two – banks or sides with water is known as valley.
ii). Via duct :-
A deep valley without continuous flowing is known as viaduct.
iii). Span :-
The center to center distance between two piers or supports is known as the span.
iv). Wing Walls
The walls constructed on the both sides of abutments are called as wing walls.They support the soil behind them or embankments of approach roads and also protect the embankments from the wave action of running water.Structures constructed as on extension of the abutments to retain the earth are called wing walls.
The structure that carry the road or railway track up to the bridge are known as approaches. Generally they are embankments.
The structure used for transferring & distributing the dead load of super structures, piers and abutments along with live loads likely to come on the bridges to the soil underneath are known as foundations.
vii). High Flood Level
The highest water level ever recorded during a flood in a river or stream is known as high flood level (HFL).
viii). Free Board
At a bridge Free board is the minimum clearance between the bottom of the girders and the design high water. In general, free board have been provided at bridges to accommodate uncertainly in the design high-water elevation.
ix). Low water Level
The lowest of minimum water level in the stream a river dry weather is known as low water level.
The rise in water level of the river near bridge due to the obstruction created by the construction of piers is called afflux.
The vertical cutting of river bed by running water is called scour.
Factor Affecting Selection Of Site.
1). At bridge site, the stream should be straight as possible.
2). The site should be geologically sound .
3). At the site, it should be the narrow stream.
4). At the site, The river flow should be without whirls & cross currents.
5). At the site, there should be suitable high banks and above high flood level.
6). The approach roads should be economical.
7). The site should be at reasonable proximity to a direct alignment of the road to be connected.
8). There should be no sharp curves in the approaches.
9). Avoidance of excessive under water construction work.
10). Large portion of bridge construction should be in dry as far as possible.
Actual factors affecting Selection of site of a bridge
1). Cost of construction.
2). Grade of Alignment.
3). Geographical conditions of the area.
4). Government Requirement.
5). Public requirements.
6). Commercial Influence.
7). Future Consideration.
8). Time Consideration.
9). Stream Characteristics etc.
Collection of Design data should know before construction of bridge
1). Name of river & road requiring bridge.
2). Name of state & district.
3). Map references of crossing points.
4). Location of nearest GTS ( great trigonometrical survey) bench mark.
5). Nature of river (Low water level & maximum depth).
6). Future Consideration.
7). Time consideration.
8). Stream Characteristics.
9). Availability of skilled and UN – skilled labor in the nearby area.
10). Seismic condition in the area.
11). Hydraulic Data ( Highest flood level).
12). Transport system for materials.
13). Availability of electrical power, telephone lines , etc.
These are the requirements must know engineer in charge during primal nary survey.
Types and Classification of Bridges
Bridges are classified on the basis of 8 factors such as :-
1). Based on materials used.
a). Timber or masonry bridge.
b). Stone bridge.
c). Steel Bridge.
d). R C C Bridge.
e). Prestressed concrete bridge.
f). Composite Bridge.
2). As per the alignment
a). Straight Alignment
When the alignment of bridge is perpendicular to the center line of a river it is called straight bridge.
b). Skew bridge
When the alignment of bridge is not perpendicular to the center line of a river it is called skew bridge.
3). As per the location of Bridge flooring
a). Deck Bridge
When the bridge flooring provided at the top of the super structure. It is called deck bridge.
b). Through Bridge
When the bridge flooring is provided at the bottom of the super structure , it is called through bridge.
c). Semi – Through Bridge
When the flooring is located at some intermediate level in the super structure it is called semi through bridge.
4). Based On Purpose
a). Aqua duct Bridge
It is small bridge constructed over a stream which remains dry for more parts of the year is called aqua duct.
b). Via duct bridge
It is a long continuous structure which carries a road or railway like bridge over dry valley composed of a series of spans bents instead of solid piers.
c). Grade separator
When there is considerable differences in their formation level and the crossing of two roads each other and , a bridge structure is constructed, which is known as grade separator.
d). High way bridge
it is constructed on a road way for the movement of vehicles.
e). Railway Bridge
It is constructed for the railway.
f). Foot bridge
The bridge is exclusively used for carrying pedestrians, cycles and animals are known as a foot bridge.
g). Pipe Bridge
The bridge is used to support pipeline for water, gas, oil etc. are known as pipe bridge.
5). Based on type of Super – structure
1). Truss Bridge.
2). Arch Bridge.
3). Cable – stayed Bridge.
4). Slab Bridge.
5). Box Girder Bridge.
6). Suspension Bridge.
1). Truss Bridge
When the flooring of bridge is supported over steel trusses is called truss bridge.Normally such type of bridges are used for railway.
Bridges with truss are made by steel two force member with only tension and compression. No bending moment is allowed in this structure. Most stable structural shape for truss in triangular.
2). Arch bridge
The bridge with abutments at each end shaped as a curved arch is known as Arch Bridge.
In such types of bridge the weight of flooring is transferred to the piers through the arch.
3). Suspension Bridge
A bridge in which the weight of the deck is supported by vertical cables suspended from further cables is called Suspension Bridge.
4). Cable – Stayed Bridge.
The bridge deck which is supported by a Cable is called stayed bridge. it has one or more towers (or phylons) .
5). Slab Bridges.
The reinforced concrete slab resting on abutments is called a short – span bridge
When the span of a bridge is 3 meter to 6 meter, slab bridge is used. It is also called Culverts.
6). Box Girder Bridges.
When the main beams comprise girders in the shape of a hollow box in a bridge the bridge known as box girder bridge or When the span of a bridge is more, flooring is supported on R C C or steel girders. Such type of bridge is called girder bridge.
6). According to HFL
i). Submersible bridge or cause way
A road causeway is a Pucca dip which allows floods to pass over it. It may oy may not have openings or vents for low water to flow.
ii). Non – Submersible bridge
In this type of bridge formation level kept above HFL, so that maximum flood does not effect the traffic on the bridge.
7). According to type of span
I). Simply Supported Bridges
When the bridge girders are simply supported on piers, it is known as simply supported bridge.
ii). Continuous bridge
When the super structure of bridge is continuous over more than two supports, it is called continuous bridge.
iii). Cantilever bridge
A cantilever bridge is form of cantilevers projecting from the supporting piers.The end of a cantilever bridge are treated as fixed.
iv). Balanced cantilever bridge
A Balanced cantilever bridge consist of spans simply supported over cantilever.
8). According to life span of bridge
i). Temporary Bridge
a). Pontoon Bridge.
b). Boat Bridge.
c). Flying Bridge.
ii). Permanent Bridge
a). R.C.C Bridge.
b). Masonry Bridge – Rajasthan.
c). Steel Bridge – Surat Tapti river.
Factors Affecting Selection of type of bridge
i). Cost and strategic conditions.
ii). Nature of the river.
iii). Sub condition of the bed of the river.
iv). Grade and alignment.
v). Hydraulic data.
vi). Climate condition.
vii). Availability of workers.
viii). Volume of nature of traffic.
ix). Cost of maintenance.
x). Probable life of structure.
xi). Foundations conditions.
xii). Length of bridge.
xiii). Width of bridge.
xiv). Live load likely to come over the bridge.
The alignment of a bridge is defined as the baseline for construction of a bridge and its approach roadway.
The alignment is also known as the center line of construction. This line is the geometric backbone of the project.
Points to be kept in mind while locating Bridge Alignment
i). The axis of bridge (alignment) should be at right angle from the river.
ii). Skew alignment should be avoided as :-
a). The piers have to resist excessive water pressure.
b). The passage of water under the super structure is not smooth & eddies are produced.
iii). The alignment should not be curved.
iv). The alignment should be such that entry and exit on the bridge should be smooth.
Economical Span is that span for which the cost of super structure for one span is equal to the cost of sub structure of that span.
Factor affecting Cost of Bridges
Cost of Bridges is actually affected by the following factors:-
i). Length of span.
ii). Nature of river to be bridged.
iii). Condition under which the bridges is to be constructed.
iv). Nature of available construction materials for the bridge.
v). Availability of skilled labors in the locality.
i). It absorbs compressive forces, destruction effects of shocks and vibration.
ii). It distributes super structure load to sub structure and allows super structure to undergoes movements without creating any harmful stresses.
iii). To avoid wear and tear action between super structure and sub structure.
iv). Increase the life span of bridge.
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