چهارشنبه ۲۸ شهریور ۰۳ | ۱۳:۱۸ ۷ بازديد
venly over the
substructure material which may not have sufficient bearing strength to
bear the superstructure load directly.
Ø Substructure
This comprises piers and abutments, wing walls or returns and their
foundation.
• Piers and Abutments
These are vertical structures supporting deck/bearing provided for
transmitting the load down to the bed/earth through foundation.
• Wing walls and Returns
These are provided as extension of the abutments to retain the earth of
approach bank which otherwise has a natural angle of repose.
• Foundation
This is provided to transmit the load from the piers or abutments and
wings or returns to and evenly distribute the load on to the strata. This is
to be provided sufficiently deep so that it is not affected by the scour
caused by the flow in the river and does not get undermined. While the
above mentioned are structurally operational parts, for safety hand rails
or parapets, guard rails or curbs are provided over the decking in order
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to prevent vehicle or user from falling into the stream or for the
separation of traffic streams.
v Classification
Bridges may be classified in many ways, as below.
Ø According to the flexibility of superstructure as fixed span bridges or
movable bridges.
• Fixed span superstructure
In case of fixed span superstructure, the superstructure remains in a
fixed position and most of the bridges are of this category.
• Movable span bridges
In case of movable span superstructure, the superstructure is lifted or
moved with the help of some suitable arrangement.
Ø According to the position of bridge floor relative to the formation level and
the highest flood discharge as deck bridges, through bridges or semi-
through bridges.
• Deck bridges
Deck-type bridges refer to those in which the road deck is carried on the
top flange or on top of the supporting girders. The deck slab or sleeper
may cantilever out to some extent beyond the extreme longitudinal
girder.
Deck Bridge
HFL
FORMATION
LEVEL
• Through bridges
In the through type bridges, the decking is supported by the bottom
flange of the main supporting girders provided on either side.
FORMATION
LEVEL
Through Bridge
HFL
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• Semi through bridges
The semi-through bridge has its deck midway and the deck load is
transmitted to the girder through the web of the girder. In this also, the
main girders are on either side of deck.
FORMATION
LEVEL
Semi-through Bridge
HFL
Ø According to the inter-span relations as simple, continuous or cantilever
bridges.
• Simply supported
Generally width of bridge is divided into number of individual spans. For
each span, the load carrying member is simply supported at both ends.
The plate girder and truss girders are used as this type of bridges. They
are suitable at places where uneven settlements of foundations are likely
to take place.
• Continuous
In continuous bridges spans are continuous over two or more supports.
They are statically indeterminate structures. They are useful when
uneven settlement of supports does not take place. In continuous bridges
the bending moment anywhere in the span is considerably less than that
in case of simply supported span. Such reduction of bending moment
ultimately results in the economic section for the bridge. In continuous
bridges the stresses are reduced due to negative moments developed at
pier or supports. Thus continuous span bridges have considerable saving
compared to simply supported bridge construction.
Following are the advantages of RCC continuous girder bridges over
simply supported girder bridges.
o As the bearings are placed on the centerline of piers, the reactions at
piers are transmitted centrally.
o It is found that the continuous girder bridge suffers less vibration and
deflection.
o The continuous girder bridge requires only one bearing at each pier as
against two bearing for simply supported girder bridge.
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o The depth of decking at mid span is reduced and it may prove to be
useful for over bridges where headroom is of prime consideration.
o The expansion joints required will be less.
o There is reduction in cost as less quantity of concrete and steel are
required.
Following are the disadvantages of RCC continuous girder bridges over
simply supported girder bridges.
o The design is more complicated as it is a statically indeterminate
structure.
o The detailing and placing of reinforcements are to be carried out with
extreme care.
o The placing of concrete and removal of formwork are to be executed
carefully in proper sequence.
• Cantilever
A cantilever bridge is formed of cantilevers projecting from supporting
piers. The ends of a cantilever bridge are treated as fixed. A cantilever
bridge combines the advantages of a simply supported span and a
continuous span. For long spans and deep valleys and at places where it
will not be practicable to use centering, cantilever bridges are more
suitable. They are suitable in case of uneven settlement of foundation.
The construction of a cantilever bridge may either be of simple type or of
balanced type.
Cantilever Span Cantilever Span
Cantilever Bridge with simple construction
In case of cantilever bridge with balanced type of construction, hinges
are provided at the points of contraflexure of a continuous span and an
intermediate simply supported span is suspended between two hinges.
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Cantilever Bridge with simple construction
Cantilever Span Cantilever SpanSimply Supported
Ø According to the form or type of superstructure as arch, beam, truss, slab,
rigid frame or suspension bridges.
• Slab
• Beam
Beam Bridge
• Girder
Girder Bridge
• Truss
The girder/beam as well as the truss can be made up of timber,
steel or concrete, or can be made up of combination of steel and
concrete.
Truss Girder Bridge
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• Arch
Barrel Type
Arch Bridge
• Suspension
Suspension Bridge
Suspension bridges are made up of high tensile steel cables strung
in form of catenaries to which the deck is attached by steel suspenders,
which are mainly made up of steel rods/members/cables. The decking
can be of timber, concrete or steel spanning across the stiffening girders
transmitting load to the suspenders.
• Cable stayed
Cable-stayed bridges are similar to the suspension bridges
excepting that there will be no suspenders in the cable-stayed bridges
and a number of these can be of masonry, concrete or steel.
Various economical span ranges for these types generally adopted
are:
Arch : For small spans of 3 to 15m in masonry, steel
arch up to 519m and concrete arches up to 305m
spans.
Slabs : Up to 9m.
Girders
and beams : 10 to 60m (exception up to 250m in continuous
construction).
Trusses : 30 to 375m simply supported and up to 550m with
cantilevered combination.
Suspension
Bridges : Over 500m up to 1400m.
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Cable
Stayed : 300 to 600m.
Ø According to the materials of construction used for superstructure as
cement concrete, prestressed concrete, steel, masonry, iron, timber or
composite bridges.
The earliest form of materials used for construction of bridges was first
stone and later brick. The masonry bridges are used for short spans and
according to availability of material and skilled labour. They are mainly of
arch type of bridges. The next form of construction was Timber Bridge in
which timber was used for spanning the gap and also for supporting the
beams. Timber bridges are used for short spans, light loads and for use as
temporary and unimportant bridges. With the invention and development of
concrete, bridges are being built entirely with concrete, either reinforced or
prestressed or a combination of both for superstructure. Many combination
of above types are also possible. The common examples of composite
construction are:
o Concrete beams reinforced with steel bars.
o Precast prestressed concrete girder with cast-in-situ RCC slab.
o Rolled steel joists topped by a cast-in-situ RCC slab.
Following are the advantages of composite bridges.
o It leads to reduction in deflection and vibrations.
o It leads to speed in construction.
o It proves to be economical.
o It results in better quality control.
o The cost of formwork is reduced.
o The cost of foundations for abutments is reduced.
o The cost of transportation is minimized.
o The overall depth of beam for a composite construction is reduced and
it leads to savings in lengths of approaches.
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Table shows the maximum spans up to which a particular type of bridge
can be recommended.
Sr.
No.
Type Maximum
span
1 RCC arch bridge 200 m
2 RCC bow-string girder bridge 45 m
3 RCC cantilever bridges with balanced type 30 m
4 RCC continuous bridge 45 m
5 RCC deck type girder bridge 20 m
6 RCC filled spandrel fixed arch bridge 35 m
7 RCC open spandrel rib type bridge 60 m
8 RCC portal frame bridge 15 m
9 Prestressed concrete arch bridge 150 m
10 Prestressed concrete continuous bridge 110 m
11 Prestressed concrete girder bridge simply
supported
55 m
12 Steel arch bridge 500 m
13 Steel bow-string girder bridge 240 m
14 Steel cable suspension bridge 1200 m
15 Steel plate girder 30 m
16 Steel rolled beam bridge 10 m
17 Steel truss bridge 180 m
Ø According to the method of clearance for navigation as bascule, lift, swing or
transporter bridges.
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• Movable – bascule bridges
In bascule bridges, the main girders are lifted together with deck
about the hinge provided on one end of the span. Depending upon the
width of channel, the bascule bridge may either be single or double.
Single Bascule Bridge
Double Bascule Bridge
• Movable – swing bridges
In swing bridges, the girders and deck can be swung about its
middle over the middle pier, clearin
substructure material which may not have sufficient bearing strength to
bear the superstructure load directly.
Ø Substructure
This comprises piers and abutments, wing walls or returns and their
foundation.
• Piers and Abutments
These are vertical structures supporting deck/bearing provided for
transmitting the load down to the bed/earth through foundation.
• Wing walls and Returns
These are provided as extension of the abutments to retain the earth of
approach bank which otherwise has a natural angle of repose.
• Foundation
This is provided to transmit the load from the piers or abutments and
wings or returns to and evenly distribute the load on to the strata. This is
to be provided sufficiently deep so that it is not affected by the scour
caused by the flow in the river and does not get undermined. While the
above mentioned are structurally operational parts, for safety hand rails
or parapets, guard rails or curbs are provided over the decking in order
PDF created with FinePrint pdfFactory trial version http://www.fineprint.com
separation of traffic streams.
v Classification
Bridges may be classified in many ways, as below.
Ø According to the flexibility of superstructure as fixed span bridges or
movable bridges.
• Fixed span superstructure
In case of fixed span superstructure, the superstructure remains in a
fixed position and most of the bridges are of this category.
• Movable span bridges
In case of movable span superstructure, the superstructure is lifted or
moved with the help of some suitable arrangement.
Ø According to the position of bridge floor relative to the formation level and
the highest flood discharge as deck bridges, through bridges or semi-
through bridges.
• Deck bridges
Deck-type bridges refer to those in which the road deck is carried on the
top flange or on top of the supporting girders. The deck slab or sleeper
may cantilever out to some extent beyond the extreme longitudinal
girder.
Deck Bridge
HFL
FORMATION
LEVEL
• Through bridges
In the through type bridges, the decking is supported by the bottom
flange of the main supporting girders provided on either side.
FORMATION
LEVEL
Through Bridge
HFL
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The semi-through bridge has its deck midway and the deck load is
transmitted to the girder through the web of the girder. In this also, the
main girders are on either side of deck.
FORMATION
LEVEL
Semi-through Bridge
HFL
Ø According to the inter-span relations as simple, continuous or cantilever
bridges.
• Simply supported
Generally width of bridge is divided into number of individual spans. For
each span, the load carrying member is simply supported at both ends.
The plate girder and truss girders are used as this type of bridges. They
are suitable at places where uneven settlements of foundations are likely
to take place.
• Continuous
In continuous bridges spans are continuous over two or more supports.
They are statically indeterminate structures. They are useful when
uneven settlement of supports does not take place. In continuous bridges
the bending moment anywhere in the span is considerably less than that
in case of simply supported span. Such reduction of bending moment
ultimately results in the economic section for the bridge. In continuous
bridges the stresses are reduced due to negative moments developed at
pier or supports. Thus continuous span bridges have considerable saving
compared to simply supported bridge construction.
Following are the advantages of RCC continuous girder bridges over
simply supported girder bridges.
o As the bearings are placed on the centerline of piers, the reactions at
piers are transmitted centrally.
o It is found that the continuous girder bridge suffers less vibration and
deflection.
o The continuous girder bridge requires only one bearing at each pier as
against two bearing for simply supported girder bridge.
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useful for over bridges where headroom is of prime consideration.
o The expansion joints required will be less.
o There is reduction in cost as less quantity of concrete and steel are
required.
Following are the disadvantages of RCC continuous girder bridges over
simply supported girder bridges.
o The design is more complicated as it is a statically indeterminate
structure.
o The detailing and placing of reinforcements are to be carried out with
extreme care.
o The placing of concrete and removal of formwork are to be executed
carefully in proper sequence.
• Cantilever
A cantilever bridge is formed of cantilevers projecting from supporting
piers. The ends of a cantilever bridge are treated as fixed. A cantilever
bridge combines the advantages of a simply supported span and a
continuous span. For long spans and deep valleys and at places where it
will not be practicable to use centering, cantilever bridges are more
suitable. They are suitable in case of uneven settlement of foundation.
The construction of a cantilever bridge may either be of simple type or of
balanced type.
Cantilever Span Cantilever Span
Cantilever Bridge with simple construction
In case of cantilever bridge with balanced type of construction, hinges
are provided at the points of contraflexure of a continuous span and an
intermediate simply supported span is suspended between two hinges.
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Cantilever Span Cantilever SpanSimply Supported
Ø According to the form or type of superstructure as arch, beam, truss, slab,
rigid frame or suspension bridges.
• Slab
• Beam
Beam Bridge
• Girder
Girder Bridge
• Truss
The girder/beam as well as the truss can be made up of timber,
steel or concrete, or can be made up of combination of steel and
concrete.
Truss Girder Bridge
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Barrel Type
Arch Bridge
• Suspension
Suspension Bridge
Suspension bridges are made up of high tensile steel cables strung
in form of catenaries to which the deck is attached by steel suspenders,
which are mainly made up of steel rods/members/cables. The decking
can be of timber, concrete or steel spanning across the stiffening girders
transmitting load to the suspenders.
• Cable stayed
Cable-stayed bridges are similar to the suspension bridges
excepting that there will be no suspenders in the cable-stayed bridges
and a number of these can be of masonry, concrete or steel.
Various economical span ranges for these types generally adopted
are:
Arch : For small spans of 3 to 15m in masonry, steel
arch up to 519m and concrete arches up to 305m
spans.
Slabs : Up to 9m.
Girders
and beams : 10 to 60m (exception up to 250m in continuous
construction).
Trusses : 30 to 375m simply supported and up to 550m with
cantilevered combination.
Suspension
Bridges : Over 500m up to 1400m.
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Stayed : 300 to 600m.
Ø According to the materials of construction used for superstructure as
cement concrete, prestressed concrete, steel, masonry, iron, timber or
composite bridges.
The earliest form of materials used for construction of bridges was first
stone and later brick. The masonry bridges are used for short spans and
according to availability of material and skilled labour. They are mainly of
arch type of bridges. The next form of construction was Timber Bridge in
which timber was used for spanning the gap and also for supporting the
beams. Timber bridges are used for short spans, light loads and for use as
temporary and unimportant bridges. With the invention and development of
concrete, bridges are being built entirely with concrete, either reinforced or
prestressed or a combination of both for superstructure. Many combination
of above types are also possible. The common examples of composite
construction are:
o Concrete beams reinforced with steel bars.
o Precast prestressed concrete girder with cast-in-situ RCC slab.
o Rolled steel joists topped by a cast-in-situ RCC slab.
Following are the advantages of composite bridges.
o It leads to reduction in deflection and vibrations.
o It leads to speed in construction.
o It proves to be economical.
o It results in better quality control.
o The cost of formwork is reduced.
o The cost of foundations for abutments is reduced.
o The cost of transportation is minimized.
o The overall depth of beam for a composite construction is reduced and
it leads to savings in lengths of approaches.
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can be recommended.
Sr.
No.
Type Maximum
span
1 RCC arch bridge 200 m
2 RCC bow-string girder bridge 45 m
3 RCC cantilever bridges with balanced type 30 m
4 RCC continuous bridge 45 m
5 RCC deck type girder bridge 20 m
6 RCC filled spandrel fixed arch bridge 35 m
7 RCC open spandrel rib type bridge 60 m
8 RCC portal frame bridge 15 m
9 Prestressed concrete arch bridge 150 m
10 Prestressed concrete continuous bridge 110 m
11 Prestressed concrete girder bridge simply
supported
55 m
12 Steel arch bridge 500 m
13 Steel bow-string girder bridge 240 m
14 Steel cable suspension bridge 1200 m
15 Steel plate girder 30 m
16 Steel rolled beam bridge 10 m
17 Steel truss bridge 180 m
Ø According to the method of clearance for navigation as bascule, lift, swing or
transporter bridges.
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In bascule bridges, the main girders are lifted together with deck
about the hinge provided on one end of the span. Depending upon the
width of channel, the bascule bridge may either be single or double.
Single Bascule Bridge
Double Bascule Bridge
• Movable – swing bridges
In swing bridges, the girders and deck can be swung about its
middle over the middle pier, clearin
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