module20120PPT.pdf

Module-1
• Introduction to bridges, classification,
computation of discharge, linear waterway,
economic span, afflux, scour depth
• Design loads for bridges, introduction to
I.R.C. loading standards, Load Distribution
Theory, Bridge slabs, Effective width,
Introduction to methods as per I.R.C.

Module-2
• Design of Slab Bridges: Straight and skew slab
bridges
Module-3
Design of T beam bridges(up to three girder only) Proportioning
of components, analysis of slab using IRC Class AA tracked
vehicle, structural design of slab, analysis of cross girder for
dead load & IRC Class AA tracked vehicle, structural design
of cross girder, analysis of main girder using Courbon’s
method, calculation of dead load BM and SF, calculation of
live load B M & S F using IRC Class AA Tracked vehicle.
Structural design of main girder.

Module-4
• Other Bridges: Design of Box culvert (Single vent
only)
• Design of Pipe culverts
Module-5
• Substructures - Design of Piers and abutments,
• Introduction to Bridge bearings, Hinges and
Expansion joints.(No design)

• Course outcomes: After studying this course,
students will be able to:
• Understand the load distribution and IRC
standards.
• Design the slab and T beam bridges.
• Design Box culvert, pipe culvert
• Use bearings, hinges and expansion joints
• Design Piers and abutments.

Program Objectives:
• Engineering knowledge
• Problem analysis
• Interpretation of data
Text Books:
1. Johnson Victor. D, “Essentials of Bridge
Engineering”, Oxford Publishing Company.
2. N Krishna Raju, “Design of Bridges, Oxford and IBH
publishing company
3. T R Jagadeesh and M A Jayaram, “Design of bridge
structures”, Prentice Hall of India

Definition of Bridge
• A bridge is a structure providing passage over an obstacle
without closing the way beneath.
• The required passage may be for a road, a railway,
pedestrians, a canal or a pipeline.
• The obstacle to be crossed may be a river, a road, railway
or a valley.

Component of Bridge Structures
Super structure Sub structure

• Super structure
Hand rails
Gaurdstone
Flooring or Wearing surfaces supported by
structural system
(Beams,Girders,arch and cable above the level of
bearing)

• Sub structure
• Abutment
• Wing walls
• Piers
• Foundation
• These structures are below the bearing level
called as substructure

1.Classification of Bridges
(According to form (or) type of
superstructures)
•Slab bridge
•Beam bridge
•Truss bridge
•Arch bridge
•Cable stayed (or )suspended bridge

2.Classification of bridges
(According to material of
construction of superstructure)
•Timber bridge
•Concrete bridge
•Stone bridge
•R.C.C bridge
•Steel bridge
•P.C.C bridge
•Composite bridge
•Aluminum bridge

(According to inter-span relationship)
•Simply supported bridge
•Cantilever bridge
•Continuous bridge

(According to the position of the bridge
floor relative to superstructures)
•Deck through bridge
•Half through or suspension bridge

(According to method of connection
of different part of superstructures)
•Pinned connection bridge
•Riveted connection bridge
•Welded connection bridge

(According to length of bridge)
•Culvert bridge(less than 6 m)
•Minor bridge(less than 6 m-60m)
•Major bridge(more than 60 m)
•Long span bridge(more than 120 m)

(According to degree of redundancy)
•Statically determined bridge
•Statically indetermined bridge

(According to anticipated type of
service and duration of use)
•Temporary bridge
•Permanent bridge

(According to function)
• Aqueduct bridge(canal over a river)
•Viaduct(road or railway over a valley or river)
•Pedestrian bridge
•Highway bridge
•Railway bridge
•Road-cum-rail or pipe line bridge

(According to road level relative to the
highest flood level of the river below )
•High-level bridge
•Submersible bridge

(According to clearance for navigation)
•High level bridge
•Movable -bascule bridge
•Movable -swing or transporter bridge

Slab and T beam Continuous span
bridge

Pre-stressed concrete Box-girder
bridge

Role of Bridge Engineer
• The bridge engineer is often involved with
several or all aspects of bridge planning,
design, and management
• The bridge engineer works closely with other
civil engineers who are in charge of the
roadway design and alignment.
• After the alignment is determined, the bridge
engineer often controls the bridge type,
aesthetics, and technical details
• The bridge engineer is often charged with
reviewing shop drawing and often
construction details

Conted…
• The owner, who is often a department of
transportation or other public agency, is charged
with the management of the bridge, either
doing the work in-house or hiring consultant.
• Bridge management includes routine
inspections, repair, rehabilitation and retrofits
or even replacement (4R) as necessary
• In summary, the bridge engineer has significant
control over the design, construction, and
maintenance processes. In return, bridge
engineer has significant responsibility for
public safety and resources

SELECTION CRITERIA FOR
BRIDGE SITE
a. A straight reach of the river.
b. Steady river flow without cross currents:
c. A narrow channel with firm banks
d. Suitable high banks above high flood level on each
side.
e. Rock or other hard in erodible strata close to the
river bed level.

f. Economical approaches danger of floods, the
approaches should be free from obstacles such as
hills, frequent drainage crossings, scared places, or
Trouble some land acquisition
g. Absence of sharp curves in the approaches;
h. Absence of expensive river training works;
i. Avoidance of excessive underwater construction.

PRELIMINARY SURVEY
Topography
Catchment area
Hydrology
Geo-technical data
Seismology
Navigation
Construction resources
Near by bridges
Traffic data

Topography
Details can be obtained from Survey of India Map.
In addition, one cross section each across the river at the
selected sites should be taken.
Catchment Area
This will also get from the same map (Survey of India)
Used mainly for the flood analysis.

Hydrologic Particulars
Study about the low water level, highest flood level , slope
of surface of water, flood velocity and discharge of river.
Data obtained from local enquiries or from the data
available for the nearest gauging site from irrigation or
flood control dept.
Navigational Requirements
 Some kind of navigation will exist on almost all major
rivers.
Study investigate about the size, density and volume of
traffic of vessels and boats so that it can be safely cross
the river without any nuisance to both the vessels and
bridge.

Geo-technical and Seismic Data
• Study perform to get the stability of the river, location
of faults, their activity and their likely repercussion on
a major structure to be put up and particulars of past
earthquakes in the site vicinity.
• Study perform also to get soil classification, grain
size and depth at which hard strata is likely to be
met with.
• Mainly Augur boring test is used to collect the soil
samples and further to study its engineering
properties.

Construction Resources
Investigation includes availability of quarry, skilled labor and
need for special equipment such as crushers, batching
plants, handling equipment etc.
Details of other Bridges Across the River
 Study conducting mainly to correlate general criteria used for
selection of sites and design of that bridge.
 Also to get the behavior of the river at existing bridges on either
reach. Will help considerably in determining the protection works,
depth of foundation, type of foundation etc required at each site.

Traffic Study
If the alternative locations can be separated by a
considerable distance, the volume and type of
traffic that will pass at each location may be different
in some cases.
Economic Point of View.
Detailed traffic survey have to be conducted to get
awareness of growth of traffic, density, volume and
future possibilities of expansion of traffic lanes etc.

Design of Bridge
Hydraulic Design Structural Design

Hydraulic Design
• Route location, Potential traffic flow, structural and
foundation details,Charcteristics of rivers and
hydrodynamic forces.
• Phase I: Site reconnaissance, Review and Analysis
of available river data with respect to proposed
communication route.
• Phase II: To conducted hydrographic and
hydraulic surveys at each of the possible bridge
sites.

Phase III : From the following data ,the following
hydraulic parameters are assessed
1. Maximum flood flow
2. Design flood flow
3. Maximum flood level
4. Navigational requirements
5. Bed and bank Characteristics
6. Approach velocity and direction
7. Flood plain Characteristics
8. River meandering characteristics

Phase IV : To study linear waterway, normal scour depth,
afflux, backwater effect, flow velocity
Phase V : Construction factors such as structural loading,
soil characteristics, economy of construction , available
manpower and materials of construction, access to the
site, prevailing climate, environmental impact ,and
Maintainers are considered.
Detailed Bridge configuration such as proper free board,
Vertical clearances, height of the bridge and
hydrodyanmice forces on the pier are estimated

Phase IV : To study linear waterway, normal scour depth,
afflux, backwater effect, flow velocity
Phase V : Construction factors such as structural loading,
soil characteristics, economy of construction , available
manpower and materials of construction, access to the
site, prevailing climate, environmental impact ,and
Maintainers are considered.
Detailed Bridge configuration such as proper free board,
Vertical clearances ,height of the bridge and
hydrodyanmice forces on the pier are estimated

Phase VI : Proposed configuration of the bridge ,
normal scour and back water effect are computed.
Phase VII : The cost of alternative schemes for
each location is appraised in this phase.
Phase VIII : To study the alternative bridge
designs for each of the possible bridge location ,the
cost of the scheme is selected for detailed design.

Backwater at a Stream Crossing

Computation of peak Flood flow
• The Maximum discharge with a bridge across a
natural stream is to be designed are as follows
1. Empherical Method
2. Rational Method
3. Area velocity method
4. Unit –hydrograph method
5. Slope Area method
6. For any available records of the flood discharge
observed at the bridge site

1. Empherical Method
When sufficient data is not available of catchment response
These developed empherical equation applicable only to the
catchment for which it is developed
Q=C×An ----------1 General equation
Dicken’s Formula
Q=C×A3/4 ----------2
Ryve’s formula
Q=C×A2/3 ----------3

Rational Method
Intensity, distribution and duration of rainfall
Catchment area ,shape, slope ,permeability and initial
wetness of the catchment
Q=A×i0×λ ----------1
λ=0.56P.f/tc+1
tc = (0.88 L3/H)0.385
P= Runoff coefficient (0.9,0.1& 0.60)
f= Correction factor for various intensity

Area velocity method
Hydraulic characteristics of the stream
Manning’s formula
Q= A×v
V= 1/n ×R0.67×S0.50

The economic span is one for which the total cost of the
bridge is minimum .
For the most economic span is the cost of superstructure
equals the cost of substructure within the following
assumption
ECONOMIC SPAN

• Assumptions
1) The cost of the superstructure is proportional
to the square of the span
2) The span of equal length
3) The cost of the abutment is same
4)The cost of each pier is same
5) The cost of railing ,parpaet approach is
constant
T=A+(n-1)B+C+D+nkl2

Where A= the cost of each abutment
B= the cost of each pier
C= the cost of railing, parapet etc
D= the cost of approach
T= Total cost of the bridge
n= the No of span
l= the length of each span
L= the total span of the bridge
K= the cost coefficient of the
superstrucre

For minimum cost dT/dl = 0
Differentiating the above equation w.r.t to l and
equating to
n=L/l
we get B=kl2
Hence for economical span le, the cost of the
superstructure of one span is equal to the cost
of the substructure of the same span
le= Square roote B/K

Afflux
• The afflux is the increasing in water level under the
bridge .
• The vertical clearance between the high flood level and
lowest point on the superstructure
• The free board is the difference between the high flood
level after allowing for afflux
• The formation level of the communication route or top
level of guide banks.

Formula used for Computing afflux
The fallowing are few formula for afflux
• Moles worth formula
• Marriman’s formula
• Drown weir formula

Moles worth formula
X=(v2/17.9+0.015)(A2/a2-1)
Where x= afflux in m
V=normal velocity of flow in m/sec
A= Area of natural water way in m2
a = The area of artificial water way in m2

• Marriman’s formula
x= v2/2g [((A/c × a) 2- A/A1]
Where
g = acceleration due to gravity
A1 = enlarged area in the upstream of the bridge in m2
c = 0.75+0.35(a/A)- 0.1(a/A)2
x= the afflux in m
v= normal velocity of flow in m/sec
A= Area of natural water way in m2
a = The area of artificial water way in m2

Drown weir formula
x=v2d2/2g (d+x2) [L2/(c2× L1
2 )-1]
Where L= natural linear water way
( Width of the stream at high flood level)
L1 = Artificial linear water way
c = discharge co-efficient which varies from
0.7 for sharp to 0.90 for bell mouth entry
d = depth of flow

Linear water way
The linear water ay is width of water way between the
extreme edges of water surface at HFL measured at right
angle to the abutment face
Streams with rigid boundaries:- When both banks and bed
are very rigid are known as Streams with rigid boundaries.
when bed and bank are very rigid the waterway of the bridge
should be made equal to the width of the water surface
measured from edge to edge along the designed High flood
level on the plotted section

Quasy alluvial streams:- Streams flowing between the
banks which are made up of rigid rock or mixture of
sand and clay ,where as the bed material is composed of
‘ loose granular material which can be picked up by the
current and transported , are known as Quasy alluvial
streams
• In this type of river the water way should be made equal
to the width of the water surface measured from edge to
edge along the designed High flood level

Alluvial stream:-
• Streams flowing between erodible banks and having
erodible beds are known as alluvial streams.
• The linear water way of bridge across a fully alluvial
streams should be
equal to the regime width as given by lacey equation

SCOUR
When the velocity of water is more than the certain
limits ,the flow carries the bed materials along with the
flow this process is called scouring
In design of piers, abutments, training work , etc for
bridge across rivers , the assessment of amount of scour
adjacent to the structure needed a care full consideration

• Bridge scour is the removal of sediment such as sand
and gravel from around bridge abutment or piers .
• Scour , caused by swiftly moving water, can scoop
out scour holes, compromising the integrity of a
structure .
• It has been estimated that 60% f all bridge failures
results from scour

• The Rivers can be classified as follows
Streams with rigid boundaries:- When both banks and bed are very rigid
are known as Streams with rigid boundaries.
Quasy alluvial streams:- Streams flowing between the banks which are
made up of rigid rock or mixture of sand and clay ,where as the bed
material is composed of ‘ loose granular material which can be
picked up by the current and transported , are known as Quasy
alluvial streams
Alluvial stream:- Streams flowing between erodible banks and having
erodible beds are known as alluvial streams.

• Local Scour at piers is caused horseshoe
vortices forming at the base of the pier.
Obstruction of flow by a pier results in a
stagnation line on the front of the pier.

Local scour
The depth of the stream measured at the middle of the channel ,
when it is in the regime condition is kwon as normal scour

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