MODULE-III INFRASTRUCTURE ENGINEERING BTCVC702

Module-3
Bridge Engineering: Sub-structures, Determination of design discharge, Linear Water Way,
Economical Span, Afflux, Scour depth, Indian Road Congress Bridge Code
Abutments: Definition, Functions, Dimensions, Types, Forces acting on an abutment,
Conditions of stability
Piers: Definition, Function, Types, Forces acting on a pier, Conditions of stability, Dimensions,
Location, Abutment pier
Wing walls: Definition, Functions, Types, Forces acting on a wing wall, Conditions of stability,
Dimensions, Precautions
Materials for sub-structures: Cement concrete, Masonry, Steel
Prepared by-
Prof. Basweshwar S. J.

3. Bridge Engineering:
• Bridge engineering is an engineering discipline branching from
civil engineering that involves the planning, design, construction,
operation, and maintenance of bridges to ensure safe and
effective transportation of vehicles, people and goods.
• Engineers who design structures must completely understand the
problem to be solved, which includes the complexities of the site
and the customer needs.
• To design for safety and longevity, engineers consider the
different types of loads, how they are applied and where.
• Engineers often aim for a design that is strongest and lightest
possible—one with the highest strength-to-weight ratio.
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• Bridge is a structure which covers a gap.
• Generally bridges carry a road or railway across a natural
or artificial obstacle such as, a river, canal or another
railway or another road.
• Bridge is a structure corresponding to the heaviest
responsibility in carrying a free flow of transport and is
the most significant component of a transportation
system in case of communication over gaps for whatever
reason such as aquatic obstacles, valleys and gorges etc.
• Bridge is the KEY ELEMENT in a Transportation System.
A bridge is a structure that spans a divide such as:
• A stream/river/ravine/valley
• Railroad track/roadway/waterway
• The traffic that uses a bridge may include:
• Pedestrian or cycle traffic
• Vehicular or rail traffic
• Water/gas pipes
• A combination of all the above
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A bridge has to carry a service (which may be highway or railway traffic, a footpath, public utilities, etc.) over
an obstacle (which may be another road or railway, a river, a valley, etc.) and to transfer the loads from the
service to the foundations at ground level.
Classifications-
• According to functions : aqueduct, viaduct, highway, pedestrian etc.
• According to materials of construction : reinforced concrete, prestressed concrete, steel, composite, timber etc.
• According to form of superstructure : slab, beam, truss, arch, suspension, cable-stayed etc.
• According to interspan relation : simple, continuous, cantilever.
• According to the position of the bridge floor relative to the superstructure : deck, through, half-through etc.
• According to method of construction : pin-connected, riveted, welded etc.
• According to road level relative to highest flood level : high-level, submersible etc.
• According to method of clearance for navigation : movable-bascule, movable-swing, transporter
• According to span : short, medium, long, right, skew, curved.
• According to degree of redundancy : determinate, indeterminate
• According to type of service and duration of use : permanent, temporary bridge, military Prepared by-

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• The substructure consists of the portion of the bridge that supports the entire structure on the given
surrounding soil.
• There are varying designs due to the different soil conditions for each bridge site and the different weights of
the structures for each project.
• In some cases, the nature of the superstructure will also influence the choice of foundation type, especially
when integral substructures are used.
• Designers are advised to involve qualified geotechnical engineers early in the bridge design process to help
select the appropriate foundation type.
3.1.1 Sub-structures
• Substructure that part of the structure, i.e. piers and
abutments, which supports the superstructure and
which transfers the structural load to the foundations.
• Foundation is the component which transfers loads
from the substructure to the bearing strata.
• Depending on the geotechnical properties of the
bearing strata, shallow or deep foundations are
adopted. Usually, piles and well foundations are
adopted for bridge foundations.
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• The substructure consists of the portion of the bridge that
supports the entire structure on the given surrounding soil.
• There are varying designs due to the different soil conditions for
each bridge site and the different weights of the structures for
each project.
Pile cap and Piles
• Pile foundation is the most commonly used foundation system
for bridges.
• Pile is a slender compression member driven into or formed in
the ground to resist loads.
• A reinforced concrete mass cast around the head of a group of
piles to ensure they act together and distribute the load among
them it is known as pile cap.
3.1.1 Sub-structures
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3.1.2 Determination of design discharge
• Estimation of design discharge for
waterway shall preferably be based,
wherever possible, on procedures evolved
from actual hydro-meteorological
observations of the same or similar
catchments.
• Bridges where damage is likely to
have severe consequences, may be
designed with flood recurrence
interval of more than 50 years.
• Bridges on less important lines or
sidings may be designed for floods
with a probable recurrence interval of
less than 50 years.
• Where Stream flow records (yearly peak
discharges) are available for the desired
recurrence interval or more – design discharge
shall be the computed flood for the desired
recurrence interval.
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3.1.3 Linear Water Way, 3.1.4 Economical Span,
• Width of waterway between the extreme edges of
water surface at H.F.L. measured at right angles to
the abutment face.
• The total width of the waterway of the bridge at
H.F.L. minus Waterway effective width of
obstruction.
• Highest flood level is the level of highest flood
ever recorded or the calculated level for design
discharge.
• The span for which the total cost of bridge will be
minimum is known as the economic span.
• Fixing length of typical span in design of bridges
across river/elevated road/metro project is very
important structural design decision.
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3.1.5 Afflux 3.1.6 Scour depth
• Bridges are built across a waterway and the structure may
be of single span or multiple spans.
• In a multiple span bridge piers need to be constructed in
the river bed.
• These piers obstruct the natural flow.
• If the obstruction is considerable, the level of water on
the upstream rises slightly compared to that at the
downstream.
• This rise in level is called afflux. Designer's calculate the
afflux and incorporate the same in the design of sub
structure so as to keep the superstructure clear of flood
water.
• Scouring can be defined as a process due to which the
particles of the soil or rock around the periphery of the
abutment or pier of the highway bridge spanning over a
water body, gets eroded and removed over a certain depth
called scour depth.
• Scouring usually occurs when the velocity of the flowing
water increases or crosses the limiting value that the soil
particles can easily handle
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3.1.7 Indian Road Congress Bridge Code
• A bridge is a structure built to span physical obstacles without closing the way underneath such as a body of
water, valley, or road, for the purpose of providing passage over the obstacle.
• Bridge engineering is a very big area, I only highlight the Indian codes used for design of reinforced concrete
road bridges in it.
In India following codes are utilized for the bridge design-
• Provision for general features of design IRC : 5 - Section I
• Provision for loads and stress IRC : 6 - Section II
• Provision for Working stress method IRC : 21 and IS : 456
• Provision for Limit state method IRC : 112 and IS : 456
• Provision for Dead load IS : 875 - Part I
• Provision for Live load IS : 875 - Part II
• Provision for Wind load IS : 875 - Part III
• Provision for Snow load IS : 875 - Part IV
• Provision for Special load and load combination IS : 875 - Part V
• Provision for Seismic load IS : 1893
Actually, these codes are mainly used for the design purpose of Reinforced concrete road bridges. The codal
provisions for Material test, Soil test, Laboratory test are not included here.
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3.2 Abutments:
3.2.1 Definition 3.2.2 Functions
• A bridge abutment is a structure which connects
the deck of a bridge to the ground, at the ends of
a bridge span, helping support its weight both
horizontally and vertically.
• Abutments are vertical structures used to retain
the earth behind the structure. The dead and the
live loads from the bridge superstructure is
supported by the bridge abutments.
• To transfer loads from a superstructure to its
foundation elements.
• To resist and/or transfer self weight, lateral loads (such
as the earth pressure) and wind loads.
• To support one end of an approach slab.
• To maintain a balance in between the vertical and
horizontal force components of an arch bridge.
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3.2.3 Dimensions 3.2.4 Types
Types of abutments include:
• Gravity abutment- resists horizontal earth pressure
with its own dead weight.
• U abutment- U-shaped gravity abutment.
• Cantilever abutment, cantilever retaining wall
designed for large vertical loads.
• Full height abutment, cantilever abutment that extends
from the underpass grade line to the grade line of the
overpass roadway.
• Stub abutment, short abutments at the top of an
embankment or slope, usually supported on piles.
• Semi-stub abutment, size between full height and stub
abutment.
• Counterfort abutment, similar to counterfort retaining
walls.
• Spill-through abutment, vertical buttresses with open
spaces between them.
• MSE systems, "reinforced earth" system: modular units
with metallic reinforcement.
• Pile bent abutment, similar to spill-through abutment.
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3.2.5 Forces acting on an abutment 3.2.6 Conditions of stability
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3.3 Piers:
3.3.1 Definition 3.3.2 Function
• Piers are vertical loadbearing members such as an
intermediate support for adjacent ends of two bridge
spans.
• In foundations for large bridges, piers are usually
cylindrical concrete shafts, cast in prepared holes,
while in bridges they take the form of caissons,
which are sunk into position.
• Piers serve the same purpose as piles but are not
installed by hammers and, if based on a stable
substrate, will support a greater load than a pile.
• It is used to support bridge superstructure and transfer the
loads to the foundation.
• The bridge piers can be constructed to be substantially
attractive and strong in order to withstand both vertical and
horizontal loads.
• It also does not hinder water flow or tide if the bridge spans
the water.
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3.3.3 Types,
Piers are categorized into two major types
based on its structure which include solid
piers and open piers.
These types are further classified into
several types:
1. Solid Piers
Solid piers possess solid and
impermeable structure, and usually
constructed from bricks, stone Masonry,
mass concrete or reinforced concrete.
Solid piers are categorized into-
a. solid masonry piers
b. solid reinforced concrete piers
Solid masonry piers-
• It is constructed from brick masonry, stone masonry, and
concrete.
• For economic reasons, the outer part of solid masonry pier is
built from stone masonry and the inner part is filled with the
help of mass concrete.
Solid Reinforced Concrete Piers-
• Solid reinforced concrete piers are mostly constructed from
reinforced concrete and commonly rectangular in cross-
section.
• It is used in the case where the height of the piers is more and
the solid masonry piers would not be strong enough to bear
the load and can be uneconomical.Prepared by-

3.3.3 Types,
2. Open Piers
Open piers permit the passage of water through the structure and classified into the following types:
2.1 Cylindrical Piers
• Cylindrical pier is constructed from cast
iron or mild steel cylinder which are
filled with concrete.
• This type of pier is suitable for bridges
with moderate height.
• In certain cases, horizontal and diagonal
steel bracing may be used to improve
stability.
2.2 Column Piers or Column Bent
• This type of piers is suitable for bridge
with significant height.
• It consists of a cap beam and supporting
columns forming a frame.
• Column bent piers can either be used to
support a steel girder superstructure or
be used as an integral pier where the
cast-in-place construction technique is
used.
2.3 Multicolumn or Pile Bent
• Multicolumn or pile bent or frame bent piers are
composed of two or more column that supports a
cap.
• Isolating footing is used for this type of piers if
the spacing between columns are large otherwise
combined footing would be more suitable.
• There is a problem of debris collection when the
water is allowed to flow between the columns.
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3.3.3 Types,
3. Masonry Piers
• This may include stone masonry and
brick masonry.
• Masonry piers are generally massive
that may lead to obstruction of linear
waterway and increase the loads on
foundations.
• Masonry solid shaft piers are built on
open raft foundation where the
possibility of scour is nil.
• Pile foundations are also possible for
such type of piers.
4. Mass Concrete Piers
• Similar to masonry piers, Mass
concrete piers massive which in turn
obstruct linear waterway and increase
loads on foundation.
• Pile foundations can be used for mass
concrete piers.
5. Reinforced and Prestressed
Concrete Piers
• Reinforced concrete or
prestressed concrete piers have
small cross- sectional area
compare with masonry and mass
concrete piers.
• That is why such pier require
much less foundation area in
addition to offering less
obstruction to waterway.
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3.3.3 Types,
6. Fixed Piers
Fixed piers support a fixed bearing and
subjected both to transverse and
longitudinal forces.
7. Free Piers
Free piers support free bearings and
transfer only axial forces from the bearing
to the foundations.
8. Cantilevered Piers
• Hammer head pier, which is also termed as
solid shaft pier, has a single solid concrete
cross section upon which a cap is placed.
• This type of pier is used to support steel
girder or precast prestressed concrete
superstructures.
• It is mostly constructed in urban areas
where space limitation is a concern.
• Not only does it aesthetically pleasing but
also occupy small spaces, thereby providing
more room for the traffic underneath.
9. Special Shaped Bent
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Forces acting on a pier, Conditions of stability,
 Self weight of pier.
 Dead loads from adjacent spans and live load reactions either from
one or from both spans whichever produces maximum effect.
 Buoyancy effect on the piers owing to pore pressure (usually taken
as 15 per cent)
 Horizontal force due to temperature effect and tractive or braking
effect acting on the top of pier.
 Horizontal force due to water-current acting on the pier at the
centre of gravity of the water pressure diagram.
 Horizontal force due to wind acting on the superstructure and the
pier at the centre of gravity of the respective wind pressure
diagram.
 Centrifugal force acting on the pier when the bridge is on a curve.
 Horizontal force due to seismic effect on the superstructure as well
as on the pier acting at the respective centre of gravity.
The combination of the above loads and forces which may act together
should be such as to produce maximum effect.
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Dimensions
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Abutment pier
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Wing walls: Definition, Functions,
• In a bridge, the wing walls are adjacent to the abutments and act as retaining walls.
• They are generally constructed of the same material as those of abutments.
• The wing walls can either be attached to the abutment or be independent of it.
• Wing walls are provided at both ends of the abutments to retain the earth filling of the approaches.
• Their design depends upon the nature of the embankment and does not depend upon the type or parts of the
bridge.
• The soil and fill supporting the roadway and approach embankment are retained by the wing walls, which can
be at a right angle to the abutment or splayed at different angles.
• The wing walls are generally constructed at the same time and of the same materials as the abutments.
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Types,
Wing walls can be classified according to their position in plan with respect to banks and abutments. The
classification is as follows:
Straight wing walls: used for
small bridges, on drains with low
banks and for railway bridges in
cities (weep holes are provided).
Splayed wing walls: used for
bridges across rivers. They provide
smooth entry and exit to the water.
The splay is usually 45°. Their top
width is 0.5 m, face batter 1 in 12
and back batter 1 in 6, weep holes
are provided.
Return wing walls: used where
banks are high and hard or firm.
Their top width is 1.5 m and face is
vertical and back battered 1 in 4.
Scour can be a problem for wing
walls and abutments both, as the
water in the stream erodes the
supporting soil.
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Forces acting on a wing wall, Conditions of stability,
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Conditions of stability,
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Dimensions-
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Precautions
(i) Wing walls parallel to abutments
This is the simplest and shortest time to build but is not the most economical design. This design has the
advantage that it has least disturbance to existing slope embankment.
(ii) Wing walls at an angle to abutments
This is the most economical design among the three options in terms of material cost.
(iii) Wing walls perpendicular to abutments
Though it is not the most economical design, the wing walls provide a continuous alignment with bridge decks
which provide supports to parapets.
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Materials for sub-structures: Cement concrete
Concrete is a construction material formed by mixing a binder, coarse aggregate, fine aggregate, water
and inorganic or organic admixture. The concrete gain its strength by hardening the binder material
due to certain chemical reactions with passage of time. However there are various type of concrete
based upon different binding material like :
• Cement concrete
• Lime concrete
• Bitumen concrete and others
Cement concrete is a type of concrete mix in which we use cement as a binding material. This cement
may be ordinary Portland cement or may be other special type of cement like high alumina cement,
rapid hardening cement, Portland slag cement depending upon particular requirement of the
construction.
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Materials for sub-structures: Masonry
• Masonry is the building of structures from individual units,
which are often laid in and bound together by mortar; the term
masonry can also refer to the units themselves.
• The common materials of masonry construction are brick,
building stone such as marble, granite, and limestone, cast
stone, concrete block, glass block, and adobe.
• Masonry is generally a highly durable form of construction.
• However, the materials used, the quality of the mortar and
workmanship, and the pattern in which the units are
assembled can substantially affect the durability of the overall
masonry construction.
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Materials for sub-structures: Steel
• Structural steel is a category of steel used for making construction materials in a variety of shapes.
• Many structural steel shapes take the form of an elongated beam having a profile of a specific cross
section.
• Structural steel shapes, sizes, chemical composition, mechanical properties such as strengths,
storage practices, etc., are regulated by standards in most industrialized countries.
• Most structural steel shapes, such as I-beams, have high second moments of area, which means they
are very stiff in respect to their cross-sectional area and thus can support a high load without
excessive sagging.
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