BRIDGES AND THEIR TYPES
INTRODUCTION OF THE
ARTICLE
A bridge is a man-made structure that avoids physical obstructions by blocking an underlying path such
as water, valley or road. It is built for the purpose of crossing the barrier.
The first man-made bridges may have been made of cut wooden logs or boards and
finally stones, using a simple support and cross-section arrangement.
The Romans built arch
bridges and waterways. They also used cement, which reduced the variation in
strength found in natural stone. The design of the bridges will vary depending
on the activities of the bridge, the nature of the terrain on which the bridge
is built, the material used to build it, and the funds available to build it.
THE MAJOR PARTS OF BRIDGES
Every
bridge can be divided broadly into three parts:
Superstructure
/
Substructure / Foundation.
Superstructure: Superstructure is a part
of a structure that supports traffic and includes decks, slabs and beams. All
parts of the bridge installed on the substructure can be called as a
superstructure.
Substructure: That
part of the structure, i.e. the piers and abutments, supports the
superstructure and transfers the structural loads to the foundations.
Foundation: The
foundation is the component that transfers load from the substructure to the
bearing strata Depending on the geotechnical characteristics of the bearing
layers shallow or deep foundations are followed. Usually, piles and well
foundations are followed for bridge foundations.
Span is
the distance between two bridge supports, be they columns, towers or the wall
of a valley.
Deck is
a bridge platform that carries loads of traffic directly. Transfers deck loads
to girders depending on deck material.
Beam/Girder a
rigid, usually horizontal, structural component
The beam or girder is a
part of the superstructure that bends at span intervals. This is the
load-bearing area that supports the deck.
Bearing: It
Transfers loads from grinders to pier caps.
Pier:
its vertical supporting structure, such as a pillar.
Pier
Cap/headstock: Is the element that transfers loads from
the superstructure to the piers. Pier cap provides sufficient seating for the Bridge
girders.
Cantilever: A
projecting structure supported only at one end, like a shelf bracket or a
diving board.
Truss: A
rigid frame made of short, straight pieces joined together to create continuous triangles or other standard shapes.
Pile
cap and Piles: Pile foundation is the most commonly used
foundation structure for bridges. The pile is a thin compression member that is
driven or formed on the ground to resist loads. This is called a pile cap to
ensure that the reinforced concrete mass cast around the head of the group of
piles works together and distributes the loads on them.
FACTORS WHICH WILL AFFECT BRIDGE STRUCTURE ARE:
Forces-Loads-Materials-Shapes
Force - Any action to maintain or alter the condition of a structure.
Compression
-
It is a force that acts to compress or reduce the size.
Tension - A
force acting to expand or extend the matter in which it operates.
Load -
weight distribution throughout a structure.
Stable
-
(adj.) Ability to resist collapse and decay; Stability (n.) Is a characteristic
of a structure that can withstand a realistic load without collapsing or
significantly deforming.
Deform
-
to change shape.
Bucking is
a sudden change (deformation) in the form of a structural component under load,
i.e. bending of a column under compression or contraction of a plate under
shear.
TYPES OF BRIDGES
All bridges are designed to allow loads to cross
obstacles. These barriers may be rivers, valleys or lakes. Loads are usually
vehicular traffic, pedestrians or animals.
There
are four basic types of bridges.
· Beam
bridges
· Arch
bridges
· Cantilever
bridges
· Suspension
bridges.
Bridges can be twisted or
bent under severe weather conditions, which can have catastrophic consequences.
To prevent this from happening the bridges must be strong enough to resist this
movement and each member of the bridge must be strong enough to withstand the
loads placed on it
Bridges
can be categorized in several different ways.
Common categories include the type of 3 structural
elements used, by what they carry, whether they are fixed or movable, and by
the materials used.
Common
types include 3 structural elements used,
· What
they carry
· Whether
they are fixed or movable
· The
materials used.
TYPE-1: FIXED OR MOVEABLE
BRIDGES
Fixed – Most
bridges are fixed bridges, which means they have no moving parts and will last
until they fail or are demolished. They have been designed where they are
considered unusable or demolished.
Temporary bridges –
Bridges made of basic modular elements on which medium or light machinery can
be moved. They are typically used in military engineering or in circumstances
where fixed bridges are repaired.
Moveable – They
have movable platforms and are often powered by electricity.
TYPE- 2 CLASSIFICATION OF
BRIDGES BASED ON STRUCTURES:
Bridges can be
characterized by how the forces of tension, contraction, bending, torque and
shear are distributed through their structure.
BRIDGES BY STRUCTURE
Arch Bridges – An arch bridge is a very popular type of
bridge that was widely used by the ancient Romans. The arch bridge is usually
made of stone, concrete or steel.
The bridge is in the shape of an arch, as the name implies. An arch bridge is a
curved bridge where the load of the arch is not applied directly downwards,
instead, the loads are carried along the curve to the end of the support. This
means that no part of the bridge will take on too much pressure. These supports
are also called abutments. The apartments carry the load of the entire bridge
and are responsible for keeping the arch in an accurate position.
No. The curves (curves) in
a bridge depending on the stress and loads that the bridge must support. The
length of curved bridges is usually up to 250 m, and the roadway structure of
the bridge.
Forces: The
compressive forces generated by the loads are shifted downward through the arch
and resisted by supports or abutments at its base. Abutment support prevents
the arch from spreading under load.
The span length of arch
bridges is normally up to 250m,
Advantages
of Arch Bridge:
1. It is easy to build with locally available material.
2. These types of bridges are very hard and very strong.
3. Arch bridges are built of various materials such as
stone, concrete and steel.
Disadvantages
of Arch bridge:
1. They take a long time to build.
2. It requires a large number of construction materials
to build.
3. Limited spans unless multiple arches (or viaducts)
are used and uneconomical use of materials
Beam bridges are
the oldest and simplest bridge design consisting of horizontal beams and vertical piers - e.g. just a simple plank
or stone slab. They are suitable only for short spans but can be used for larger
crossings by adding additional piers.
Forces: As
the bridge is loaded, by transport, the beam bends, causing the upper surface
to shrink and the lower surface to stretch or tension.
Beam bridges have span less
than 80m.
Advantages:
They are easy to build and cheap compared to other bridge types, and therefore
more common.
Disadvantages:
They have a certain spacing and do not allow large boats or vehicles to go
under.
Truss Bridge is a triangle assembly.
Truss bridges are usually made from a series of straight steel bars.
Rigid arms extend from both
sides of two piers. Diagonal steel tubes, protruding from the top and bottom of
each pier, hold the arms in place. The arms that go towards the center are only
supported on one side, like very strong diving boards. These “diving boards”
called cantilever weapons, support a central span.
Truss Bridges are
structures made by joining lengths of material together to form an open
framework - based primarily on triangles due to their rigidity. They are very
strong and can support heavy loads.
Forces: As
with Beam Bridge, a loaded truss top is placed in compression and the bottom in
tension. These forces are divided among the right-angled members.
The
span length of truss bridge is in between 50m-110m.
Advantages
of Truss Bridge:
1. This type of bridge is easily built in the factory
and then built on site.
2. Ships or supports are relatively low compared to the
Beam Bridge,
3. They are strong and tough and very light in weight
with efficient use of materials.
Disadvantages
of truss bridges:
1. Highly skilled professionals are needed to design
this.
2. In terms of design they are more complex than beam
bridges.
Cantilever bridges are based on horizontally
projected structures in space supported only at one end - like a springboard.
Forces: if
two cantilevers project out from a central pier the forces are balanced.
Cantilever bridge has a
span in between 150m-500m.
Advantages
of Cantilever Bridge:
1. These types of bridges
are accepted only when support cannot be provided at certain levels.
2. Support is required only
on one side of the cantilever.
Disadvantages
of Cantilever Bridge:
1. Cantilever bridges
undergo major breakthroughs during construction.
2. If the forces are not in
balance, the bridge may hook.
Tied arch bridges have an arch-shaped
superstructure, but differ from conventional arch bridges. Instead of
converting the weight and transport loads of the bridge into propulsion forces,
the ends of the curves are controlled by the tension in the country under the
structure. These are similar to arch bridges, but they transfer the weight and
transport load of the bridge to the upper chord which is attached to the lower
cords at the foundation of the bridge. They are often called bowstring arches
or bowstring bridges.
Suspension Bridges Key Elements is A pair of
main suspension cables extend over two towers and are attached to an anchor
buried deep in the ground at each end. Small vertical suspender cables are
connected to the main cables.
Forces: Any
load applied to the bridge is converted into a tension in the main cables,
which must be firmly anchored to resist.
The span length of
Suspension bridge is in between
150m-2000m
Advantages:
Strong and can spread over long distances across rivers.
Disadvantages:
The build is expensive and complicated
Cable-stayed bridges may look similar to
suspension bridges, but in reality they are completely different in principle
and in their construction. There are two main classes of cable-stayed bridges:
fan type, which are more efficient, and harp or parallel type, which allow more
space for adjustments.
Forces: As
traffic on the road is pushed down, the cables connected to the road shift the
loads to the towers, keeping them short. The tension in the cables continues to
act as they are stretched as they are connected to the roadway.
The
span length of Cable-stayed bridge is in between
500m-1000m.
Advantages
of cable-stayed bridge:
1. It is very economical compared to the suspension bridge.
2. It is good for medium spaces and can be easily
created by exiting the tower.
Disadvantages
of cable-stayed bridge:
1. Maintenance and inspection can be very difficult.
2. These types of bridges are not suitable for long
distances.
Roving Bridge/Change line Bridge/Turnover bridge Is a bridge over a canal
constructed to allow a horse towing a boat to cross the canal when the towpath
changes sides.
TYPES OF BRIDGES BY
USE
Car
Traffic bridge: The most common type of bridge, with two or
more lanes designed to carry car and truck traffic of various intensities.
Pedestrian
bridge: They are usually made in urban environments or in
terrain inaccessible to car traffic (rough hills, forests, etc.).
Double-decked
bridge: Built to provide better flow of traffic on water or
rough terrain. Most of the off they have high car lanes, sometimes with an area
dedicated to railroad tracks.
Train
bridges: Bridges made specifically to carry one or multiple lane
of train tracks.
Pipelines: Bridges
made to carry pipelines across water or inaccessible terrains. Pipelines can
carry water, air, gas and communication cables.
Viaducts: A viaduct is made up of multiple bridges
connected into one longer structure. Ancient structures created to carry water
from water-rich areas to dry cities.
Commercial
bridges: Modern bridges that host commercial buildings such as
restaurants and shops.
FAQs
1.
What are the types of bridges based on materials?
Types of Bridges by materials used:
• Natural
materials
• Wood
• Stone
• Concrete
and Steel
• Advanced
materials
2.
What are the types of bridges based on structures?
·
Arch Bridges
·
Beam bridges
·
Truss Bridge
·
Cantilever bridges
·
Tied arch bridges
·
Suspension Bridges
·
Cable-stayed bridges
·
Roving
Bridge/Change line Bridge/Turnover Bridge
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