design of bridge

Abstract

ANALYSIS AND DESIGN OF T-GIRDER BRIDGE
AT
BALKUMARI, KATHMANDU-LALITPUR

Full text

TRIBHUVAN UNIVERSITY
Institute of Engineering
SAGARMATHA ENGINEERING COLLEGE
Sanepa, Lalitpur
DEPARTMENT OF CIVIL ENGINEERING
Final Project report on
ANALYSIS AND DESIGN OF T-GIRDER BRIDGE
AT
BALKUMARI, KATHMANDU-LALITPUR
Supervisor
ER. SUDIP PATHAK
Prepared by
DHARMENDRA TELI (072/BCE/14)
KRISHNAA SHRESTHA (072/BCE/20)
SHEKHAR NATH CHAPAGAIN (072/BCE/41)

01 December 2019
TRIBHUVAN UNIVERSITY
Institute of Engineering
SAGARMATHA ENGINEERING COLLEGE
Sanepa, Lalitpur
DEPARTMENT OF CIVIL ENGINEERING
This is to certify that the final year project entitled “ANALYSIS AND DESIGN OF T-
GIRDER BRIDGE” was submitted to the DEPARTMENT OF CIVIL ENGINEERING in
the partial fulfilment of requirement for the degree of Bachelor in Civil Engineering. The
project was carried under special supervision and within the time frame prescribed by the
syllabus.
....……….. ………….…
Er. Sudip Pathak External Examiner
Project Supervisor
…………
Er. Arun Prasad Parajuli

Head of Department, Department of Civil Engineering
ACKNOWLEDGEMENT
We would like to express deep gratitude to everyone who helped us to complete our final year
project on topic Analysis and Design of T-girder Bridge. Without the immense support of you
all, the completion of project in this short frame of time would not have been possible.
To begin with, we would like to thank our college Sagarmatha Engineering College
engineering for giving us this opportunity to do final year project on this topic. We would like
to specially thank our project supervisor Er. Sudip Pathak sir for guiding us throughout our
work and helping us to complete our project in time.
Also, we are extremely thankful towards Er. Arun Prasad Parajuli (HOD), Er. Bhuwan
Ghimire (DHOD) other teachers, who laid foundations on structure during B.E. courses
through semesters 1st through 8th.
Finally, we would like to thank Er. Birendra Prakash Gupta for his guidance and all the
persons who helped us directly and indirectly in completion of this report. We also
acknowledge our gratitude towards each other for such a united co-ordination amongst the
group members during the project.
Project Group Members
Dharmendra Teli (072/BCE/014)
Krishnaa Shrestha (072/BCE/020)
Shekhar Nath Chapagain (072/BCE/041)
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ABSTRACT
In this project, we aim to analyze and design a T-girder bridge by using the theory of
structure, bridge Engineering, and foundation engineering. Theories of foundation
engineering for sub-structure and theories of bridge engineering and live loading
recommended by IRC forms the base of our design.
The knowledge of foundation engineering, Influence lines, and Theory of structures are
essential for the analysis and design of this project. IRC and IS code guidelines were
preferred for the design purpose.
The superstructure (RC slab, T-beam girder and cross girder) and sub-structure (RCC
abutment and pier) components have been designed using working state of design method
under class AA, 70R and class A loading as prescribed by IRC. Pigeaud’s method was used in
analysis of the slab. limit state method of design was used for design of pier shaft.
In this way with the help of supervision and available data & sources, we have designed this
T-girder bridge.
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TABLE OF CONTENT
CERTIFICATE………………...………………………………………………………i
ACKNOWLEDGEMENT……......…………………………………………………...ii
ABSTRACT …………………….……………………………………………………iii
1. INTRODUCTION..................................................................................................1
1.1 Background...............................................................................................................1
1.2 Objectives.................................................................................................................1
1.3 Scope of Work & Limitations...................................................................................2
2. METHODOLOGY.................................................................................................4
2.1 Acquisition of data....................................................................................................4
2.1.1 Site selection survey..........................................................................................4
2.1.2 Topographical survey........................................................................................4
2.1.3 Geotechnical Investigation................................................................................5
2.1.4 Hydrological Data:............................................................................................6
2.2 Loading IRC loads for the bridge design:...............................................................13
2.3 Components of Bridge:...........................................................................................14
2.3.1 Superstructure.................................................................................................14
2.3.2 Substructure....................................................................................................16
2.4 Idealization and Analysis of bridge structure..........................................................24
2.4.1 Influence Line Diagram..................................................................................24
2.4.2 Design of Deck Slab........................................................................................25
2.4.3 Design of T- Girder.........................................................................................28
2.5 Selection of bridge and its components...................................................................29
2.6 Method of Design of Bridge...................................................................................30
3. TOPOGRAPHICAL SURVEY.............................................................................31
4. HYDROLOGICAL STUDY................................................................................33
4.1 Selection of Discharge of River..............................................................................33
4.2 Linear water way.....................................................................................................36
4.3 Scour depth calculation...........................................................................................37
5. GEOTECHNICAL INVESTIGA.........................................................................40
BIBLIOGRAPHY........................................................................................................42
CODES/STANDARDS................................................................................................43
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SLIENT FEAURE
NOTATIONS
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Name of the project Analysis and design of T-Girder bridge
Location
State 3
District Kathmandu-lalitpur
Municipality Kathmandu And Lalitpur
Geographic Location
Reduced level 1291 m
Classification of road Urban road
Type of road surface Bituminous
Terrain type Valley
Information on the
Structure
Total length of bridge 78.7 m
Span arrangement 3* 25 m
Total width of the bridge 11 m
Number of lanes Two
Width of
Carriage way 7.5 m
Footpath /kerb 1.75+1.75
Types of Superstructure RCC T-Girder Bridge
Types of bearing Elastomeric Pad Bearing
Types of abutment RCC Cantilever Type
Type of Pier Hammer Head
Design Data
Live load IRC class AA(wheel and Track)
IRC Class A
IRC 70 R (wheel and Track)
Net Bearing Capacity of
soil
300 KN/m2
Catchment Area 83 Sq km
Design Discharge 378.48m3/sec.
Lacey’s Waterway 77.818m
Contracted Waterway 69 m
HFL 1287.4 m
LBL 1283.4 m
Scour Depth
Abutment 4.67 m
pier 7.21 m

ф Diameter of Bar
τuv Shear Stress
Ag Gross Area
Ah Horizontal Seismic Coefficient
Ast Area of Steel in Tension
Asv Area of Stirrups
bf Flange width
bw Web width
d Effective depth
d’ Effective Cover
D Overall Depth
E Young’s modulus of Elasticity
fck Characteristic Strength of Concrete
fy Characteristic Strength of Steel
I Importance Factor
Ip Polar Moment of Inertia
Ld Development Length
pc Percentage of Steel in Compression
pt Percentage of Steel in Tension
R Response Reduction Factor
Sa/g Average Response Acceleration Coefficient
Sv Spacing of Stirrups
Xu Actual depth of Neutral Axis
Xul Ultimate depth of Neutral Axis
Z Zone Factor
ABBRIVIATION
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LL Live Load
WC Wearing Coat
DL Dead load
RCC Reinforced Cement Concrete
IRC Indian Road Congress
HFL High Flood Level
LBL Lower Bed Level
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1. INTRODUCTION
1.1 Background
Bridge, a civil engineering structure, a structure used since ancient times for crossing any
obstruction beneath it. Who would have imagined that a simple structure used for crossing
obstruction will be used in so many ways with so many materials involved that it will become
such a large field of study at this period of time. Today, bridge is one of the most prominent
civil engineering structures. Different types of bridge are being built these days due to
sophisticated equipment and developed material science.
In context of Nepal, being a mountainous country with a lot of river and rivulets, we need
many bridges just to join one part of the country to another. Therefore, we need to construct
many bridges to ease the extension of road network as well as to carry out other development
works in an efficient way. Therefore, there is a huge potential of bridge engineering in Nepal.
In this project, we were assigned to design a bridge over Bagmati River connecting the roads
"Baneshwor - Sankhamul - Balkumari - Road" at balkumari joining Kathmandu District with
Lalitpur District. As it is a quite busy urban road, two lanes for design are minimal. We are
supposed to design the most economic bridge for this section based on the various data
collected by us. This report is prepared as a part of project work for the fulfillment of the
Project-II as per the syllabus of Bachelor of Civil Engineering fourth year second part.
In Nepal, mostly RCC T-beam superstructure is preferred as the resources to design and
construct are readily available in Nepal. For our project purpose, we have also designed RCC
T-beam Bridge for learning the bridge engineering skills and practice. The variation in design
procedures for the superstructures, bearings and substructures has helped us to enhance our
understanding of the essentials of Bridge Engineering.
1.2 Objectives
The main objectives are to analyze and design the bridge based on Working State method of
design. In addition to that, before start of the work we came with following objectives:
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To obtain the basic ideas of bridge building.
To be familiar with the different types of bridge and its design principles.
To know about various type of loading and their forms of application.
To understand various methods used in the design of the structural components of
bridge and their limitations.
To be familiar with the design standards and code specifications of bridge
To be familiar with the standard specification regarding the design of bridge.
The main objective of this project is to design a bridge over Bagmati River by using the
Working State approach of design. Hence, we entitled name of this project as “Design of
T- Girder at balkumari, Kathmandu- Lalitpur”.
1.3 Scope of Work & Limitations
The assignments done while designing the proposed RC T-beam bridge design are:
Study of topographic, geological, hydrological, geotechnical and traffic study of
bridge site.
Visit of bridge site and preparation of site observation report including verification of
data required.
Carryout design and detailing of selected bridge type.
Design of appropriate bearing.
Design of abutment and pier.
Design of foundation.
Preparation of detail drawing of bridge superstructures with its all components,
abutments, pier, bearing and footing required for the construction of selected bridge
type.
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Limitations
In Nepal, T-beam Bridge is highly preferred but it has some limitations as:
It is only economic for spans less than 30 m
Due to presence of large girders and its arrangement, it has less clean appearance.
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2. METHODOLOGY
2.1 Acquisition of data
For the design of our bridge, the preliminary data needed was acquired after carrying out
different surveys.
2.1.1 Site selection survey
• A straight reach of river.
• Steady river flow without whirls and across currents.
• A narrow channel with firm banks.
• Sustainable high banks above high flood level on each side.
• Rock or other hard in-erodible strata close to the river bed level.
• Proximity to a direct alignment of the road to be connected.
• Absence of sharp curves in the approaches.
• Absence of expensive river training works.
• Avoidance of excessive underwater construction
In selection of site, care should be taken to investigate a number of probable alternative sites
and then decide on the site which is likely to serve the needs of the bridges at the least cost.
2.1.2 Topographical survey
Topographical survey was carried out for detailed engineering survey of the proposed bridge
site. Total station, reflector and measuring tape were usually used for detailed survey.
After consultation with the technical personnel and the local villagers and as directed by the
river morphology; an axis joining line joining left bank and right bank was fixed.
The bridge site detailing area covers a suitable region along the length of river both upstream
and downstream. It also covers left and right banks along the existing approach roads.
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2.1.3 Geotechnical Investigation
Geotechnical investigation is one of the major parts of the project work for the design of the
proposed bridge at Bagmati River in Kathmandu & Lalitpur district. Geotechnical
investigation works includes core drilling, test pitting, visual investigation at site. For our
project this was not quite possible. Thus, the geotechnical data were adopted suitable with our
locality and as per the similar works done in the region. However, we carried out the sieve
analysis of the bed soil, finding out its mean size, specific gravity and water content.
Vertical Clearance above H.F.L
For the high-level bridges, a vertical clearance should be allowed between the H.F.L, and the
lowest point of the superstructure. This is required to allow for any possible error in the
estimation of the H.F.L., and the design discharge. It also allows floating debris to pass under
the bridge without damaging the structure
The difference between the vertical clearance and the free-board is sometimes not clearly
understood. While vertical clearance is the difference in level between H.F.L. and the lowest
point of the superstructure, freeboard is associated with the approaches and guides bunds. The
freeboard at any point is the difference between the highest flood level after allowing afflux,
if any, and the formation level of the embankment on the approaches or the top level of guide
bunds at that point, for high level bridges, the freeboard should not be less than 600 mm.
Scour Depth
Scour of stream bed occurs during the passage of a flood discharge, when the velocity of
stream exceeds the limiting velocity that can be withstand by the particles of the bed material.
The scour depth should be measured with reference to existing structures near the proposed
bridge site, if this is possible. Due allowance should be made in the observed value for
additional scour that may occur due to the designed discharge being greater than the flood
discharge for which the scour was observed, and also due to increased velocity due to
obstruction to flow caused by the construction of bridge.
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When the above practical method is not possible, the normal depth of scour may be computed
by equation for natural streams in alluvial beds
d =0.473(Q/f).33
Where,
d = normal depth of scour below H.F.L. for regime conditions in a stable
channel in meters.
Q=designed discharge in m3 per second
The minimum depth of foundation is kept at:
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1.27×d for abutments
2×d for piers (IRC 78:2014)
2.1.4 Hydrological Data:
The Hydrological data was acquired from the secondary sources and the
calculation of maximum discharge of the river was calculated using the
following method
A). Rational method:
A rational formula for flood discharge should take into account the intensity, distribution and
duration of rainfall as well as the area, shape, slope, permeability and initial wetness of the
catchment (drainage basin). The area of the catchment is a major contributing factor for the
runoff. The shape of the catchment affects the peak discharge, long and narrow basins
yielding less than pear shaped basins. Steep slopes result in shorter time of concentration than
flatter slopes.
Many complicated formulae are available in treaties on hydrology. A typical rational formula
is:
Q = AIoλ
Where, Q =maximum flood discharge in m^3 per second
A =catchment area in square kilometers
Io =peak intensity of rainfall in mm per hour
λ = a function depending on the characteristics of the
catchment in producing the peak runoff
=
0.56 Pf
tc+1
tc = time of concentration in hours
= (0.87*L3/H)0.385
L = distance from the critical point to the bridge site in kilometers
H = difference in elevation between the critical point and bridge site in kilometers
P = coefficient of run-off for the catchment characteristics.
f = a factor to correct for the variation of intensity of rainfall Io over the area of the
catchment.
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B) Area velocity method:
The area velocity method based on the hydraulic characteristics of the stream is probably the
most reliable among the methods for determining the flood discharge. The velocity obtaining
in the stream under the flood conditions is calculated by Manning’s or similar formula:
Manning’s formula is used here. The discharge Q is given by equation:
Q = A×v
Where, Q=Discharge in m3/s
A = Wetted area in m2
v = Velocity of flow in m/s
= (1/n)×R2/3S1/2
n = manning's coefficient calculated from table
S = slope of the stream
R = Hydraulic mean depth in meters
=
Since the cross section of the stream is usually plotted with different scales for horizontal and
vertical distances, the wetted perimeter cannot be scaled off directly, but has to be calculated.
The wetted line is divided into a convenient number of parts and the partial length along the
perimeter computed as hypotenuse of the right triangle with the horizontal and vertical
lengths of the element as the two sides. The sum of such parts give the wetted perimeter P.
Similarly the wetted area (A) is calculated as the sum of the partial areas of the elements
obtained as the product of the horizontal interval and the mean depth to bed below the flood
level considered at the two ends of the element. The hydraulic mean radius can then be
computed as A/P.
The quantity ‘S’ in the Manning’s equation denotes the slope of the stream and is a difficult
quantity for evaluation. The normal practice is to compute the slope from the bed levels at
two cross sections over a long distance. This may lead to unreliable results, since it is difficult
to take any particular level in the cross section as the bed level. So it is advised to compute
the bed slope of the stream from the low water levels or water levels at any one time at the
proposed site and at one section each upstream and downstream of the proposed site.The
success or otherwise of the use of this method depends on the correct determination of the
flood levels. Considerable judgement tempered with experience will be called for in order to
correctly assess the evidence in this connection. If the railway track is near the bridge site, the
maximum flood mark will be usually available from the markings of railway cross drainage
works. In the case of new road formation in sparsely inhabited or underdeveloped areas, the
investigation engineer has to come to his conclusion on the maximum flood level based on
his evaluation of the evidence from the elderly inhabitants of the area and the observation of
the banks, deposit of debris on tree trunks, etc.
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C) Inglis Formula:
This formula is based on the flood data of catchments in Western Ghats in Maharashtra.
The peak flood Q in m3/s is expressed as
Q=
124 A
√
A+10.4
Where, A=catchment area in square km
D) WECS formula:
In Nepalese context, Water and Energy Commission Secretariat (WECS) has developed
empirical relationships for analyzing flood of different frequencies. The discharge formula for
100 year of return period is given by:
Q = 14.63(A3000+1)0.7342
Where, Q = Maximum discharge in m3/s
A3000 = Basin area below 3000 m elevation in square kilometers
E) Ryves formula (1884):
According to Ryves, maximum discharge is given by:
Q = CR×A2/3
Where, Q = maximum discharge in m3/s
A = Catchment area in sq. km.
CR = Ryves coefficient
This formula was originally developed for Tamil Nadu region, is in use in Tamil Nadu and
parts of Karnataka and Andhra Pradesh. The values of CR recommended by Ryves for use are
CR = 6.8 for areas within 80 km from the east coast
= 8.5 for areas which are 80-160 km from the east coast
= 10.2 for limited areas near hills
F) Dickens Formula (1865):
Dickens formula for discharge calculation is given by:
Q = CD×A3/4
Where, Q = maximum flood discharge (m3/s)
A = Catchment Area (km2)
CD=Dickens constant with the value of 6 to 30
Following are some guidelines in selecting the value of CD:
CD= 6 for North-Indian plains
= 11-14 for North Indian Hilly Regions
= 14-28 for Central India
= 22-28 for Coastal Andhra and Orissa
For actual use, the local experience will aid in the proper selection of CD. Dickens formula is
used in the central and northern parts of the country.
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G) Fuller’s Formula (1914):
Fuller’s formula is derived for catchments in USA are a typical empirical method which is
given by:
Q = Cf×A0.8(1+0.8log10T)
Where, Q=maximum discharge in m3/s
Cf = a constant which varies from 0.18 to 1.88
T = Return period in yrs.
A = Catchment Area in sq. km.
For Nepal, the value of Cf is taken as 1.03.
H) Modified Dicken’s Formula:
Using Dicken’s method, the flood discharge can be calculated by using the formula:
Q = CT×A0.75
Where, Q= maximum flood discharge in m3/s
CT = Modified Dicken’s constant proposed by the Irrigation Research Institute, Roorke,
India, based on frequency studies on Himalayan rivers which is computed as
CT = 2.342log (0.67T) log (1185/P) +4
P=100× (a+6)/ (A+a)
a= perpetual snowfall area in sq. km.
T=Return period in years
Calculation of Linear Waterway, Scour Depth and High Flood Level (HFL)
a) Calculation of linear waterway:
When the water course to be crossed is an artificial channel for irrigation or navigation, or
when the banks are well defined for natural streams, the linear waterway should be full width
of the channel or the stream.
For large alluvial stream with undefined banks, the required effective linear waterway may be
determined using Lacey’s formula:
P = C√Q
Where, P = the effective linear waterway in meters
Q = the designed maximum discharge in m3/s
C = a constant usually taken as 4.8 for regime channel, but may vary
From 4.5 to 6.3 according to the local conditions
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The effective linear waterway is the total width of the waterway of the bridge minus the mean
submerged width of the piers and their foundation down to the mean scour level. It is not
desirable to reduce the linear waterway below that for regime condition. If a reduction is
affected, special attention should be given to the afflux and velocity of water under the
bridge. With reduced waterway, velocity would increase and greater scour depths would be
involved, requiring deeper foundations. Thus any possible saving from a smaller linear
waterway will be offset by the extra expenditure on deeper foundations and protective works.
In view of the deficiencies of the assumptions made in the computations for design discharge
and for the effective waterway by Lacey’s formula, it is often prudent to adopt the full natural
width for the linear waterway, taking care not to succumb to the trap of overconfidence in
apparently precise methods of calculation
b) Calculation of scour depth:
Scour may be defined as the removal of material from the bed and banks of streams during
the passage of flood discharge, when the velocity of the stream exceeds the limiting velocity
that can be withstood by the particles of the bed material. If the bridge and its approaches do
not constrict the natural flow, the scour will be small. On the contrary, when the designer
attempts to reduce the waterway, severe scour usually results during the extraordinary flood
conditions.
The scour is aggravated at the nose of the piers and bends. The maximum depth of scour
should be measured with reference to existing structures near the proposed bridge site, if this
is possible. Such soundings are best done during or immediately after the flood. Due
allowance should be made in the observed values for additional scour that may occur due to
design discharge being greater than the flood discharge for which the scour was observed,
and also due to increased velocity due to obstruction of flow caused by the construction of
bridge. When the above practical method is not possible, the mean depth of scour may be
computed by the given equation for natural streams in alluvial beds:
dsm = 1.34
Where, dsm = mean depth of scour below HFL in meters
Db = discharge in m3/s per meter width, obtained as the toal design
Discharge divided by the effective linear waterway
Ksf = silt factor for a representative sample of the bed material, as in the table below taken as
1.76 times the square root of the particle size in mm (weighted mean diameter of the particle
determined as indicated in Appendix 2 of IRC:(5-1998).
In order to provide an adequate margin of safety, the design discharge for the above
calculation is increased by 30%, 25 to 20%, 20 to 10% and 10% for catchment areas of below
500 sq. km, between 500 and 5000 sq. km, between 5000 to 25000 sq. km and over 25000 sq.
km, respectively. When the effective linear waterway L is less than the regime width W, the
value of dsm computed from the above mentioned formula is to be increased by multiplying
the same by the factor (W/L)0.67.
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The maximum depth of scour D below the HFL is to be taken as below:
dsmax = 2.0dsm for pier
= 1.27dsm with approach retained or lowest bed level whichever is deeper for
abutment
= 2.0dsm for scour all round for abutment
dsmax = 2.0dsm in the right-angled bend
= 1.75 dsm at the severe bend
= 1.5 dsm at moderate bend
= 1.27dsm in a straight reach
The minimum depth of foundations below HFL is kept at 1.33 D for erodible strata. If the
river is of a flashy nature and the bed does not submit readily to the scouring effects of the
floods, the maximum depth of scour should be assessed by observations and not by the above
calculations.
When a bridge is located close to the mouth of a river joining the sea, the possibility exists
for the situation of the high tide opposing the flood discharge, resulting in heading up of the
water level in the river. At the end of the high tide, the flood discharge may be relatively
sudden, which may cause scour in excess of the values computed by the above equation to
calculate the average scour depth. Considerable engineering judgements is required in
assessing the required depth of foundation in such cases.
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c) Calculation of afflux:
Afflux is the heading up of water over the flood level caused by constriction of waterway at a
bridge site. It is measured by the difference in levels of the water surfaces upstream and
downstream of the bridge. Afflux can be computed from the equation as follows:
x =
v2
2g
(
L2
c2L1
2−1
)
Where, x=afflux
v=velocity of normal flow in the stream
g=acceleration due to gravity
L= width of stream at HFL
L1= linear waterway under the bridge
c = coefficient of discharge through the bridge, taken as 0.7 for sharp
Entry and 0.9 for bell mouthed entry
The afflux should be kept minimum and limited to 1 to 1.5 m. afflux causes increase in
velocity on the downstream side, leading to greater scour and requiring deeper foundations.
The road formation level and the top level of guide bunds are dependent on the maximum
water level on the upstream side including afflux.
The increased velocity under the bridge should be kept below the allowable safe velocity for
the bed material.
d) Calculation of High Flood Level (HFL):
The HFL of river was determined using Manning’s equation and cross sectional drawing of
river at bridge axis through iterative procedure.
Finally, with all the collected and computed data, the design of the bridge was done as per the
prevailing Bridge codes .
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2.2 Loading IRC loads for the bridge design:
According to IRC: 6-2014, road bridges and culverts are classified on the basis of loadings
that they are designed to carry.
IRC class AA loading
This loading is to be adopted within
certain limits, in certain existing or
contemplated industrial areas, and along
certain specified highways and areas.
Bridges designed for class
loading should be checked for class A
loading is considered in each lane.
IRC class A loading
This loading is normally considered on
all in which dominant bridges and
culverts are constructed. One train of
class A loading is considered in each
lane
IRC class B loading
This loading is normally considered
when the structure is temporary and for
bridges in specified area. Structures with
timber spans are to be regarded as
temporary structures.
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2.3 Components of Bridge:
2.3.1 Superstructure
The basic function of bridge superstructure is to permit the uninterrupted smooth passage of
traffic over it and to transmit the loads and forces to the substructure safely through the
bearings. Although it is difficult to stipulate the aesthetic requirements, it should, however, be
ensured that the type of superstructure adopted is simple, pleasing to the eye, and blends with
the environment.
The superstructure of any bridge must be designed such that it satisfies geometric and load
carrying requirements set forth by its owner. This geometric requirement depends upon the
number and width of traffic lanes and footpaths that have to be carried across. They also
depend on overall alignment and various horizontal and vertical clearances required above
and below the roadway. The superstructure designed has to meet various structural design
requirements such as strength, stiffness and stability.
The horizontal and vertical alignment of a bridge is governed by the geometrics of the
highway, roadway or channel, it is crossing. For girder type bridges, the girders may either be
curved or straight, and may be aligned on chords between supports with the deck slab built on
the curve. The following points require close examination when girders are aligned on a
chord:
Non-symmetric deck cross section
Deck finish of the warped surface
Vertical alignment of the curbs and railings, to preclude visible discontinuities
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Proper development of super elevation
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The various components of superstructure and their limiting dimensions with function as per
IRC 5 is given as follows:
I .Lighting
The lighting of the bridge is generally in accordance with the provisions of the authority
having jurisdiction on that area.
II .Drainage
The transverse drainage of the roadway is usually accomplished by providing suitable crown
in the roadway surface, and the longitudinal drainage is accomplished by camber or gradient.
III .Traffic lane
Roads designed for traffic flow can be single lane, double lane or more. Road width in meters
should be divided by 3.65 and the quotient approximated to the nearest whole number of
design traffic lanes. We have designed our bridge with two traffic lane.
IV.Road width
Road width is the distance between the roadside faces of the kerb which depends on the
number and width of traffic lanes and the width of the bounding hard shoulders. For our
project, we have designed road width of 11 m.
V .Footpaths
Footpaths or walkways are generally provided where pedestrian traffic is anticipated, but not
on major arteries or in country sides. Its width is 1.5 m generally, but may be as narrow as 0.6
m and as wide as 2.5 m depending on the requirements. For our project, we have designed
footpath of 1.75 m wide and 275 mm deep.
VI. Road kerb
The road kerb is either surmountable type or insurmountable type. In the absence of
walkways, a road kerb is combined with parapet.
VII.Parapets
Parapets can be of many shapes and of variable sturdiness. They are designed to prevent a
fast moving vehicle of a given mass from shooting off the roadway in the event of an
accidental hit. Their height varies, but it should be at least 700 mm.
VIII. Railing Post
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The parapets are usually mounted by metal Railing Post, about 350 mm high. Their roadside
face is double sloped. For our project, we have designed handrail of size 200×200×1200
mm .
IX.Crash barriers
Sometimes walkways are protected from the vehicular traffic by crash barriers which act as
insurmountable kerbs and deflect the hitting vehicles back into the traffic lane.
X .Expansion and roadway joints
To provide for expansion and contraction, joints should be provided at the expansion end of
spans, at other points, where they may be desirable. Joints are preferably sealed to prevent
erosion and filling of debris.
XI. Medians
On expressways and freeways, the opposing traffic flows are separated by median strips.
These reduce the possibility of accidents due to head on collisions.
XII. Super-elevation
The super-elevation of the surface of a bridge on a horizontal curve is provided in accordance
with the applicable standard. This should preferably not exceed 0.06 m per meter, and never
exceed 0.08 m per meter
2.3.2 Substructure
Substructure of a bridge refers to that part of it which supports the structure that carries
the roadway or the superstructure. Thus substructure covers pier and abutment bodies
together with their foundations, and also the arrangements above the piers and abutments
through which the superstructure bears on the structure. The latter are called bearings.
i) Foundation: A foundation is that part of the structure which is in direct contact
with the ground and transmits loads to it. A footing is that part of the foundation
that transmits the loads directly to the soil.
18 | P a g e

Types of Foundations:
A. Deep Foundations
Deep foundations generally have depth greater than the width. They are constructed by
various special means. They are of following types:
Piles
Piles are essentially giant sized nails that are driven into the subsoil or are
placed in after boring holes in the subsoil. The giant sized nails that are driven
into the subsoil or are placed in after boring holes in the subsoil. The giant
sized nails are made of concrete, steel or timber and can be square,
rectangular, circular or H-shaped in section. A group of piles is capped
together at top, usually by a reinforced concrete cap, to support the pier of
crapped together at top, usually by a reinforced concrete cap, to support the
pier or abutment body above.
Caissons or wells
Caisson is constructed at open surface level in portions and sunk
downwards mechanically by excavating soil from within the dredge hole all
the way till its cutting edge reaches the desired founding level. The well is
then effectively scaled at bottom and at least partly filled by sand. The surface
level and the portions near it are capped. The pier or abutment is then
constructed on the cap.
B. Shallow Foundations
A foundation is shallow if its depth is less than or equal to its width. These are
generally placed after open exaction, and are called open foundations. The design of
open foundations is based on complete subsoil investigations. But in case of low safe
bearing capacity of soil, such foundations have to be disallowed. The selection of the
appropriate type of open foundation normally depends upon the magnitude and
disposition of structural loads, requirements of structures (settlement characteristics,
etc.), type of soil or rock encountered, allowable bearing pressures, etc. Where rocky
stratum is encountered at shallow depths, it may be preferable to adopt open foundations
because of its advantage in permitting proper seating over rock and speed of
construction work. They are of following types:
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Spread Footing (Isolated footing, combined footing, strip footing)
An isolated footing is a type of shallow foundation used to transmit the load of an
isolated column to the subsoil. This is the most common type of foundation. The base
of the column is enlarged or spread to provide individual support for the load.
A spread footing which supports two or more columns is termed as combined footing.
The combined footing may be rectangular in shape if both the columns carry equal
loads, or may be trapezoidal if they carry unequal loads. If the independent spread
footings of two columns are connected by a beam, it is called strap footing. A strap
footing may be used where the distance between the columns is so great that a
combined trapezoidal footing becomes quite narrow.
The strap footing consists of single continuous R.C. slab as foundation of two or
three or more columns in a row. It is suitable at locations liable to earthquake
activities. It also prevents differential settlement. In order to have better stability a
deeper beam is constructed in between the columns. It is also known as continuous
footing.
Mat or Raft Footing
A raft or mast is a footing that covers the entire area beneath a structure and supports
all the walls and columns. When the allowable soil pressure is low or the loads are
heavy the use of spread footings would cover more than one half of the area and it
may prove more economical to use mat or raft foundation. The mat or raft tends to
bridge over the erratic deposits and eliminates the differential settlement. It is also
used to reduce settlement above highly compressive soils, by making the weight of
structure and raft approximately to weight of soil excavated.
c) Bearings: Bearings are provided in bridges at the junction of the girders or slabs and
the top of pier and abutments. Bearings transmit the load from the superstructure to
substructure in such a way that the bearing stresses developed are within the safe
permissible limits. The bearings also provide for small movements of the superstructure.
The movements are induced due to various reasons such as:
Movement of the girders in the longitudinal direction due to variations
in the temperature
The deflection of the girder causes rotations at the supports
Due to sinking of the supports the vertical movements are developed
20 | P a g e

Movements due to shrinkage and creep of concrete
In the case of prestressed girders, prestressing the girders cause movements of girders
in the longitudinal direction.
Types of Bearings
I. Fixed Bearings
Fixed bearings permit rotations while preventing expansion. They are of the following
types:
Steel Rocker bearing
R.C. Hinge bearing
II. Expansion Bearings
Expansion bearings accommodate both horizontal movements and rotations, they are of
following types:
Sliding Plate bearing
Sliding cum Rocker bearing
Steel Roller cum Rocker bearing
R.C Rocker cum Roller bearing
Elastomeric bearing
Elastomeric Bearing
Elastomeric bearings are widely used in present times as they have less initial and
maintenance cost. Besides occupying a smaller space, elastomeric bearings are easy to
maintain and also to replace when damaged, chloroprene rubber termed as neoprene is
the most commonly used type of elastomer in bridge bearings. Neoprene pad bearings
are compact, weather resistant and flame resistant. Hence, nowadays elastomeric
bearings have more or less completely replaced steel rocker and roller bearings.
iii. Pier
The bridge supports in between the abutment supports are referred to as piers. The choice
of construction of the bridge deck will dictate the choice of the type of pier. If support is
required at intervals across the full width of the bridge deck, then some form of
supporting wall or portal frame is made for the pier. However when deck has some
capacity within itself to span transversely at an intermediate support positions by means
of a diaphragm within the depth of the deck, there is wider choice available for pier.
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Simplicity in the formation of a pier not only has the merit of providing easier and more
economical construction, but it is also likely to produce more attractive result. But for
some special cases, complex shapes may be adopted. In this case the bearings are placed
at the heads or the feet of the piers.
Types of Pier
Depending on the type, size and dimensions of the superstructure, the following types of
piers are in general use:
I) Solid type pier : The solid type pier is generally built using brick or stone masonry or
concrete. This type with cut ease water is widely used for river bridges.
II) Trestle type pier : The trestle type pier comprises of a number of reinforced concrete
columns with a concreting cap at the top. The trestle type of pier finds wide applicability
in the case of flyovers and elevated roadways generally used for crossing in city roads.
III) Hammer head pier: It consists of a massive single pier with cantilever caps on
opposite sides resembling the head of a hammer. This type of pier is generally suitable
for elevated roadways and when used in river bridges, there is minimum restriction of
waterway.
IV) Cellular type pier
For the construction of massive piers carrying multilane traffic, it is economical to use
cellular type reinforced concrete piers which results in the savings of concrete. However
cellular type piers require costly shuttering and additional labor for placing of
reinforcements. For tall piers, slip forming work can be adopted for rapid construction.
V) Framed type pier
R.C. type piers are aesthetically superior and rigid due to monolithic joints between the
vertical, inclined and horizontal members. These type of piers are ideally suited to reduce
the span length of main girders on either side of center line of the pier resulting in
savings in the cost of superstructure. However this type of construction requires two
expansion joints at close intervals with increase of maintenance cost.
Forces acting on piers
The various forces to be considered in the design of piers are as follows:
1. Dead load of superstructure and pier.
2. Live load of vehicles moving on the bridge.
3. Effect of eccentric live loads.
4. Impact effect for different classes of loads.
5. Effect of buoyancy on the submerged part of the pier.
22 | P a g e

6. Effect of wind loads acting on the moving vehicles and the superstructure.
7. Forces due to water current.
8. Forces due to wave action.
9. Longitudinal forces due to tractive effort of vehicles.
10. Longitudinal forces due to braking of vehicles.
11. Longitudinal forces due to resistance in bearings.
12. Effect of earthquake forces.
13. Forces due to collision for piers in navigable rivers.
The stability analysis for the piers is generally made by considering some of the critical
forces which will have significant effect on the stresses developed in the piers.
Design of pier
The salient dimensions of pier like the height, pier width and batter are determined as
follows:
I) Height
The top level of pier is fixed to 1 to 1.5m above the high flood level, depending upon the
depth of water on the upstream side. Sufficient gap between the high flood level and top
of pier is essential to protect the bearings from flooding.
II) Pier Width
The top of pier should be sufficient to accommodate the two bearings. It is usually kept
at a minimum of 600 mm more than the outer to outer dimension of the bearing plates.
III) Pier Batter
Generally the sides are provided with a batter of 1 in 20 to 1 in 24. Short piers have
vertical sides. The increased bottom width is required to restrict the stresses developed
under loads within safe permissible values.
IV) Cut and Ease Waters
The pier ends are shaped for streamlining the passage of water. Normally the cut and
ease waters are either shaped circular or triangular.
iv. Abutment
Abutments are end supports to the superstructure of a bridge. Abutments are generally
built using solid stone, brick masonry or concrete. An abutment has three distinct
structural components:
a. Breast wall
b. Wing wall
23 | P a g e

c. Back wall
The design of abutment is done precisely in the same manner as the design of pier. The
dimensions are first determined from the practical point of view and its stability is
subsequently tested. The important additional force which the abutment has to withstand
is the earth pressure of the earth filling behind the abutment. The minimum top width of
the abutment should be 3 to 4 feet with the front batter of 1 in 24 and back batter of 1 in
6. Eddies erode the toes of the bank behind the abutment and thus the cost of
maintenance of the road is increased. In order to overcome this defect and give the
smooth entry and exit to the water, splayed wing walls to the abutment are constructed.
Function
To finish up the bridge and retain the earth filling
To transmit the reaction of the superstructure to the foundation.
Design
Height: Height is kept equal to that of piers.
Abutment batter: The water face is kept vertical or a small batter of 1 in
24 to 1 in 12 is given. The earth face is provided with a batter of 1 in 3 to
1 in 6 or it may be stepped down.
Abutment width: The top width should provide enough space for bridge
bearings and bottom width is dimensioned as 0.4 to 0.5 times the height
of the abutment.
Length of abutment: The length of abutment must be at least equal to
the width of the bridge.
Abutment cap: The bed block over the abutment is similar to the pier
cap with a thickness of 450 to 600 mm.
Forces acting on abutment
Dead load due to superstructure
Live load due to superstructure
Self weight of the abutment
Longitudinal force due to tractive effort and braking
Forces due to temperature variation
Earth pressure due to backfill
Abutment should be designed in such a way that it can resist the forces mentioned above.
24 | P a g e

d) Appurtenances and site related structures:
Appurtenances are parts of the bridge or bridge site which are non-structural components
and serve in the overall functionality of the structure.
i) Embankment and slope protection structure: Structure which provide proper
drainage, control erosion and increase aesthetics of bridge.
ii) Approach slab: Slab, which provides smooth transition of loads from flexible road
surface to rigid bridge surface.
iii) River training structure: Structure, which guide and regulate the river course in
desired direction and protects bridge substructures.
2.4 Idealization and Analysis of bridge structure
2.4.1 Influence Line Diagram
Usually the structures are analyzed for loads which do not change their points of application
on the structure. Very often structures have to be analyzed for a number of parallel moving
loads which keep on changing their positions on the structure. In such cases the internal
stresses in the structure at any given point, which depend on the positions of the loads, keep
on varying as the loads take up different positions on the structure.
A typical instance is a bridge loaded with a number of moving vehicles, which are then said
to constitute a train of wheel loads. In order to design such structures, it is not enough to
analyse the structure for a given position of loads and calculate the stress resultants namely:
bending moments, radial and normal shear forces at any section in a member of the structure.
The engineer must know the maximum values of stress resultants, both positive and
negatives, at any section of the structure. Sometimes the designer would even like to know
the maximum deflection at a given point when a structure is subjected to moving loads.
25 | P a g e

The maximum value of the stress resultants or the deflection at a given section could be
found by taking a number of trial positions of the loads. Such a procedure apart from being
time consuming is also uncertain. The task is very much simplified by using the concept of
influence line.
An influence line is a graph or curve showing the variation of any function such as reaction,
bending moment, shearing force, deflection etc. at a given point of a structure, as a unit load
parallel to a given direction, crosses the structure.
The direction of the moving unit load depends on the nature of loading to be expected in the
structure.
Use of Influence Line Diagram
Using the principle of superposition, the following two types of problems can be solved with
the help of influence lines:
First, if the influence line for a function is known, its value for a given position of a
number of parallel moving loads can be found.
The second application is of far more practical importance, influence lines can be
used to locate very easily that particular position of a number of parallel moving loads
on a structure, which will give the maximum positive or maximum negative value of a
function at a given point on the structure.
26 | P a g e

2.4.2 Design of Deck Slab
Pigeaud’s method is used for the analysis of slabs spanning in two directions for the bridge
design as the bridge design receives heavy patch load.
Hence, Pigeaud's method is most appropriate for the design of deck slab.
Analysis of slab decks
I . Slab spanning in one direction
For slabs spanning in one direction, the dead load moments can directly be computed
assuming the slab to be simply supported between the supports. Bridges deck slabs have to be
designed for I.R.C. loads, specified as class AA or A depending on the importance of the
bridge. For slabs supported on two sides, the maximum bending moment caused by a wheel
load may be assumed to be resisted by an effective width of slab measured parallel to the
supporting edges. For a single concentrated load the effective width of dispersion may be
calculated by the equation
beff = K×x(x-x/L) + bw
Where,
beff = Effective width of slab on which load acts
L= effective span
x = Distance of center of gravity from nearer support
bw = Breadth of concentration of load
K = a constant depending on the ratio (B/L) and is compiled
in IRC 21
II. Slab spanning in two directions
In the case of bridge decks with tee beams and cross girders, the deck slab is supported on all
four sides and is spanning in two directions. The moments in two directions can be computed
by using the design curves developed by M. Pigeaud.
The method developed by Pigeaud is applicable to rectangular slabs supported freely on all
four sides and subjected to a symmetrically placed concentrated load as shown in the figure
below.
The notations used are as follows: L = long span length
B = short span length
u, v = dimensions of the load spread after allowing for
dispersion through the deck
K = ratio of short to long span = B/L M1= moment in short span direction M2= moment
in long span direction
m1 and m2 = coefficient of moment along long and short direction
27 | P a g e

µ = poison’s ratio for concrete generally
assumed as 0.15
W = wheel load under consideration.
The dispersion of the load may be assumed
to be at 45⁰ through the wearing coat and
deck slab according to IRC: 21code
specifications. Consequently, the effect of
contact of wheel or track load in the
direction of span shall be taken as equal to
the dimension of the tyre contact area over
the wearing surface of the slab in the
direction of slab plus twice the overall
depth of the slab inclusive of the thickness
of the wearing surface. It is sometimes assumed to be at 45⁰ through the wearing coat but at
steeper angle through the deck slab. The bending moments are computed as:
M1= (m1+ µm2)×W
M2= (m2+ µm1)×W
Figure Dispersion of wheel load through wearing coat
28 | P a g e

The values of the moment coefficients m1 and m2, depend upon parameters (u/B), (v/L) and
K.
Curve to compute moment coefficients of slabs completely loaded uniformly distributed load
or dead load of slab for different values of K and 1/K is also given below. The Pigeaud’s
curves used for the estimation of the moment coefficients m1 and m2 for value of k= 0.5 used
in our design are as follows:
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2.4.3 Design of T- Girder
A very simple, popular and powerful method to analyze girder for live load in simply
supported T-beam bridges is Courbon’s method.
Courbon’s method is popular due the simplicity of the computations and is applicable when
the following conditions are satisfied:
The ratio of span to the width of bridge greater than 2 but less than 4
The longitudinal girders are interconnected by at least 5 symmetrically spaced cross
girders.
Depth of transverse beam should be at least 0.75 times the depth of main beam.
Hence, we adopted Courbon’s method for the analysis and design of girders.In Courbon’s
method, it is assumed that the transverse profile of the bridge deck under loading remains
straight & load shared by each girder in central region of bridge deck is found by the
distribution factors.When the live loads are positioned nearer to the kerb as shown in figure
the CG of live load acts eccentrically with the CG of the girder system. Due to this
eccentricity, the loads shared by each girder is increased or decreased depending upon the
position of girder. This is calculated by Courbon’s theory by reaction factors given by,
Rx =
∑W
n
*(1+∑I/∑d2*I)*dx*e)
Rx= reaction factor for the girder under consideration
I = MOI of each longitudinal girder
30 | P a g e

dx= distance of girder under consideration from the central axis of the bridge
W= total concentrate live load
n = number of longitudinal girders
e = eccentricity of live load w. r.t the axis of the bridge
The live load bending moments and shear forces are computed for each of the girders. The
maximum design moments and shear forces are obtained by adding the live load and dead
load bending moments. The reinforcement in the main longitudinal girders are designed for
the maximum moments and shears developed in the girders.
2.5 Selection of bridge and its components
I ) T-beam bridge
In context of Nepal, T-beam bridges are highly preferred and are much more in practice than
other bridges. Due to economic cost, usability up to 30 m span, locally available resources
and ease in construction with fewer requirements of highly skilled manpower and
sophisticated equipment T-beam was preferred for design purpose.
II) Elastomeric bearing
Since our bridge span length is 25 m, the superimposed load was comparatively less due to its
short span length, elastomeric bearings are used. They have less initial and maintenance cost.
Besides occupying a smaller space, elastomeric bearings are easy to maintain and also to
replace when damaged, chloroprene rubber termed as neoprene is the most commonly used
type of elastomer in bridge bearings. Neoprene pad bearings are compact, weather resistant
and flame resistant.
III) Reinforced concrete abutment
Our height of abutment is above 6 m and hence, reinforced concrete abutment is preferred.
IV.Hammerhead type pier
Due to high surcharge load and height of pier more than 6 m hammer head type pier was
selected.
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2.6 Method of Design of Bridge
Due to abundant use in the construction of RCC bridges all over Nepal, availability of and
recommendation from our supervisor, we used Working State Method for the design of bridge
components. However, for the design of piers, we used the Limit State Method as it was more
convenient than the Working State Method.
32 | P a g e

3. TOPOGRAPHICAL SURVEY
Topographical survey was carried out to prepare topographical map for pertinent information
that may be required for design, construction and maintenance.
Centre line of proposed bridge site:
After consultation with the technical personnel and the local villagers and as directed by the
river morphology; an axis joining line joining left bank and right bank is fixed.
Benchmarks
The reference benchmark was established to start with the survey works. The suitable and
convenient place for starting bench mark was marked as BM1 on the permanent concrete
pillar which is situated near by the bridge site on left bank of the river.
Figure Google earth image showing bridge site
33 | P a g e

Site Topography
The area is mostly densely populated, with very less natural terrain but roads
and structures.
The site has mild slope of 1 in 1000. The bridge facilitates the 7.5m wide road
connecting Baneshwor – balkumari – sankhamul. There is also a road
running under the bridge, along the river on the Kathmandu side. The road
might suffer rare floods with higher return period. there is an suspension
bridge at the bridge site.
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4. HYDROLOGICAL STUDY
4.1 Selection of Discharge of River
The discharge of the river was computed using various method described in the
methodological section
1) Rational Method
QP=
C∗I∗A
3.6
Where
I= rainfall intensity
C= coefficient of rainfall
A= catchment area in km2
Q=flood discharge
I=
K T a
(tc+b)n
; T=
1
P
=100
Where,
K=5.92, a=0.162, b=0.5, n=1.013
tc= 0.019478 L0.77S-0.385
L= length of stream in km =28km
H= difference in elevation of remotest point of the basin and outlet in m
= 2325-1282.21
= 1042.79
S=slope of stream =H/L
=
1042.79
28000
0.03724
tc = 0.019478* 280000.77 *0.03724-0.385
= 183.58mins
Now,
I =
183.58
60 +0.5
¿
¿
¿
5.92∗1000.162
¿
= 3.449mm/hr
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Q =
c∗i∗A
3.6
=
0.8∗3.449∗83
3.6
= 6.361488m3/sec
2) Gumbel Method
S.N Discharge(m3/sec) (X-X)2S.N Discharge(m3/sec) (X-X)2
1 72.70 283.417 11 67.70 476.767
2 87.0 6.426 12 52.60 1364.194
3 97.6 65.044 13 84.30 27.405
4 99.40 97.318 14 76.50 169.911
5 98.60 82.17 15 80.70 78.057
6 96.40 47.1282 16 73.40 260.338
7 177 7650.12 17 75 211.266
8 100 109.516 18 100.50 120.23
9 74.60 223.054 19 93.10 12.709
10 68.10 459.459 20 115.50 674.1812
∑ X = ∑(X-X)2N=20
1790.7 12418.716
36 | P a g e

X=
∑ X
n
=
1790.7
20
=89.535
σx =
∑(X−X)2
N−1
= 25.565
For N=20
From table
Yn= 0.5236
Sn=1.0628
For
T=100yrs
Yt= -ln (ln (
T
T−1
))
Y100 = -ln (ln (
100
100−1¿
) =4.6
K100= (y100-yn)/Sn
= (4.6-0.5236)/1.0628
=3.835
Q100 =x+k100*σ
=89.535+3.835*25.565
= 187.576m3/sec
37 | P a g e

3) Modified Dicken’s Method
QT=CTA0.75
Where,
A=total catchment area=83sq.km
CT =2.342 log (0.6T)log(
1185
p¿
+4
P =100*
a+6
A+a
Where,
a=perpetual snow area =0
so,
p=100*
6
83
=7.2289
CT=2.342*log (0.6*100) log(
1185
702289 ¿
+4
= 13.227
QT=CT*A0.75
=13.227*830.75
= 363.722m3/sec
4) Fuller’s method
Qmax=QT*(1+2(A/2.59)-0.35)
Where,
Qav*(1+0.8logT)
Now,
Qav=Cf*A0.8
= 1.03*(83)0.8
Qav=35.326m3/sec
QT=35.326*(1+0.8*log (100))
= 91.8476m3/sec
Qmax=91.8476(1+2(83/2.59)-0.3)
= 156.765m3/sec
5) WECS method
Q2=1.876(A300+1)0.8783
For 100year return period
Q100=14.63(A300+1)0.7342
=14.63(83+1)0.7342
38 | P a g e

= 378.486m3/sec
6) Slope Area Method
Selection of Design flood
S.N Method Flood discharge (m3/sec)
1 Rational 63.61
2 Gumbel method 187.576
3 Modified Dicken’s Method 363.722
4 Fuller’s Method 156.765
5 WECS Method 378.486
6 Slope area Method 376.093
39 | P a g e

From table the least discharge calculated by rational method is minimum and discharge
calculated by WECS method is high. Thus, the flood flow for 100yr s for return period is
consider for design with flow of 378.48m3/sec.
The HFL corresponding to 378.48m3/sec is 1287.4m
4.2 Linear water way
i) kellerhal’s formula
B= 3.26Q1/2
= 3.26*(378.48)1/2
= 63.42m
ii)Lacey’s formula
W=C*Q1/2
= 3.5*(378.48)1/2
= 77.818m3/sec
Contracted water way =77-2*2-2*2
= 69m
From the table of slope area method
Check for the velocity
Bed level =1283.4m
HFL Level=1287.4m
H =4m
Q = 378.48m3/sec
So,
V=2.66m3/sec
Check for Afflux
X=
v2
2g
*
L2
C2∗L12
¿
-1)
Where,
L= HFL width =57.95
40 | P a g e

C= constant as per shape
=0.7, for sharp entry
= 0.9, for bell mouth
L1=linear water way
Now,
X=
2.662
2∗9.81
*
57.952
0.92∗612
¿
-1)
= 0.0411m<3m ok
HFL including Afflux = 1287.4+0.0411=1287.4411m
4.3 Scour depth calculation
dsm= 1.34*(
q2
f¿
where,
q=Q/B
Q=Q+30% of Q
= 378.48+30%*378.48q
=492.024m3/sec
Measured width =50m
Calculated width=77.818m
From design discharge, width=57.95m
Contracted water way =69m
So,
q= (492.024/69) =7.1307m3/sec/m
f=1.76*
√
dm
dm=1.1
f=1.845
dsm=1.34*(
q2
f¿
0.33
= 1.34*((
7.13072
1.845 ¿¿
0.33
= 4.00307
Maximum scour depth for abutments=1.27*4.00307=5.0838m
Maximum scour depth for pier =2*4.00307=8.00614m
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Or,
1.33D=1.33*4.00307=5.234
Maximum scour depth level around abutments=HFL-depth
= 1287.4-5.1589
= 1282.2411m
Maximum scour depth level around pier=1287.4-8.00614
= 1279.3939m
According to IRC special publication 13:
D = 0.473*(
Q
f
)0.33
= 0.473*(492.024/1.845)0.33
=2.988m
Regime width (w)= 4(Q)1/2
= 4(378.48)1/2
= 77.818m
D'=D*(W/L)0.61
=2.988*(77.818/69)0.61
= 3.215m
Maximum scour depth for abutments =1.27*3.215
= 4.083m
Maximum scour depth for pier =2*3.215=6.43m
Or,
1.33D=1.33*3.215=4.27595
Maximum scour depth level around abutments =1287.4-4.179475
= 1283.22m
Maximum scour depth level around pier=1287.4-6.43=1280.97m
Then,
Average of maximum scour depth around abutments= (1283.22+1282.241)/2
= 1282.73m
Average of maximum scour depth around pier = (1280.97+1279.3939)/2
=1280.1819 m
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5.
5.
5.
5.
5.
5.
5.
5.
5.
5.
5.
5.
5.
5.
5.
5.
5.
GEOTECHNICAL INVESTIGA
Fig :- Geological Map of Nepal
The bridge site lies in the Tibetan Tethys Zone. Furthermore, Kathmandu valley being a
drained lake, possess alluvial soil and sedimentary rocks beneath. However, due to the river
action, we can find eroded evidences of sedimentary rocks as well as silty sand deposits.
Soil/Bearing Capacity
The average particle size of soil particles was found to be 1 mm through sieve analysis with
the following characteristics.
Summary of soil investigation:
Water content = 11.94 %
Specific gravity = 2.645
Sieve Analysis Curve (depth 0.0-0.5m)
The bearing capacity of soil was adopted to be 350 KN/m2 by observing the general soil
properties and similar works done in the region.
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BIBLIOGRAPHY
1. Nepal Road Standards (First Revision, 2045), Department of roads, Kathmandu, 2045.
2. IRC:21-2000, Standard Specification and Code of Practice for Road Bridges, Section
III-Cement concrete (Plain and Reinforced), Third Revision.
3. IRC:6-2016, Standard Specification and Code of Practice for Road Bridges, Section IILoad
and stress (Seventh Revision).
4. IRC:78-2014, Standard Specification and Code of Practice for Road Bridges, Section
VII-Foundation and Substructures (Revised Edition).
5. IRC:5-2015, Standard Specification and Code of Practice for Road Bridges, Section I
General Features of Design (Eight Revision).
6. IS code 456-2000
7. SP -16
8. D. Johnson Victor, Essential of Bridge Engineering
9. IS 1893 : 1984, Criteria for earthquake resistant design of structures.
10. K.R. Arora, Soil Mechanics and Foundation Engineering
11.Design Examples Provided by Asso. Prof. N.C. Sharma, IOE, Pulchowk
12 .N.Krishna raju, Design of Bridges, Oxford and IBH Publishing Company Pvt. Ltd., New
Delhi
13. Design Example Provided by Er. Birendra Prakash Gupta
14. Final Report on Design and build of Manohara River Bridge,volume I
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CODES/STANDARDS
Following codes were followed during the course of our bridge design :-
Codes Uses
IRC : 5 – 2015 (Section I) General feature of design
IRC: 6- 2016 (Section II) Load and load combination
IRC: 21-2000 (Section III) Cement concrete
IRC : 78- 2014 (Section VII) Foundation and substructure
IRC : 83- 1987 (Section IX) Bearings
SP 16 RCC
IS 456-2002 Plain and Reinforced concrete
Nepal bridge standard
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