Lecture No. 1-A

7/31/2019 Lecture No. 1-A

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Bridge Planning

Traffic Studies

Hydrotechnical Studies

Geotechnical Studies

Environmental Considerations

Alternatives for Bridge Type

Economic Feasibility

Bridge Selection and Detailed Design


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Traffic Studies

City Center

New Bridge

New Road Link

Existing Network


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Traffic Studies

Traffic studies need to be carried out to

ascertain the amount of traffic that willutilize the NeworWidenedBridge

This is needed to determine Economic

Feasibility of the Bridge For this Services of a Transportation

Planner and or Traffic Engineer areRequired

Such Studies are done with help of TrafficSoftware such as TransCAD, EMME2 etc.


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Traffic Studies

Traffic Studies should provide following

information Traffic on Bridge immediately after opening

Amount of traffic at various times during life of the

Bridge

Traffic Mix i.e. number of motorcars, buses, heavy

trucks and other vehicles

Effect of the new link on existing road network

Predominant Origin and Destination of traffic that will

use the Bridge

Strategic importance of the new/improved Bridge


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A thorough understanding of the river and

river regime is crucial to planning of Bridgeover a river

Hydrotechnical Studies should include:

Topographic Survey 2km upstream and2km downstream for small rivers includingLongitudinal section and X-sections

For big rivers 5kms U/S and 2kms D/Sshould be surveyed

Navigational Requirements


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Scale of the topographic map

1:2000 for small rivers

1:5000 for large rivers

The High Flood Levels and the

Observed Flood Level should beindicated map

Sufficient Number of x-sections

should be taken and HFL and

OFL marked on them

River Bed surveying would

require soundings


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Catchment Area Map

Scale recommended 1:50,000 or

1:25,000

Map can be madeusing GT Sheetsavailable from Surveyof Pakistan

All Reservoirs, RainGauges Stns., RiverGauge Stns., shouldbe marked on map Catchment of River Indus


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River Catchment Area


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River Catchment Boundaries with Tributaries


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River Catchment Boundaries with Sub-Basin Boundaries


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Hydrological Data

Following Hydrological Data should be

collected: Rainfall Data from Rain Gauge Stations in

the Catchment Area

Isohyetal Map of the Catchment Areashowing contours of Annual Rainfall

Hydrographs of Floods at River GaugeStations

Flow Velocities

Sediment Load in River Flow during floods


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Hydrologic Data

Example of an ISOHYETAL MAP


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Hydrologic Data

Example of River Hydrograph


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Hydrologic Data

Example of a River Hydrograph


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Design Flood Levels

AASHTO Gives Following Guidelines for Estimating

Design Flood Levels


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Design Flood Levels

AASHTO Gives Following Guidelines for Estimating

Design Flood Levels


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Design Flood Levels

CANADIAN MINISTRY OF TRANSPORTATION

Gives Following Guidelines for Estimating Design Flood Levels


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Design Flood Levels


Gives Following Guidelines for Estimating Design Flood Levels


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Design Flood Levels


Gives Following Guidelines for Estimating Freeboard Requirements

FREEBOARD REQUIREMENTS


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Estimating Design Flood

Flood Peak Discharge at Stream or River Location

Depends upon: Catchment Area Characteristics

Size and shape of catchment area

Nature of catchment soil and vegetation

Elevation differences in catchment and between catchmentand bridge site location

Rainfall Climatic Characteristics

Rainfall intensity duration and its spatial distribution

Stream/River Characteristics Slope of the river

Baseline flow in the river

River Regulation Facilities/ Dams, Barrages on the river


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Methods of Estimating Design Flood

1. Empirical Methods

2. Flood Frequency Analysis

3. Rational Method


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Empirical Methods of Peak Flood Estimation

Empirical Formulae have been determined that

relate Catchment Area and other weather orriver parameters to Peak Flood Discharge

Popular Formulae for Indo-Pak are:

Dickens Formula4/3

825 AQ Q = Discharge in Cusecs

A = Catchment Area in Sq. Miles

Inglis Formula4

7000

A

AQ

Ryves Formula 3/2ACQ

C = 450 for areas within 15 miles off coast

560 between 15 100 miles off coast


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Flood Frequency Analysis Method

Usable at gauged sites where river

discharge data is available for sufficienttime in past

Following Methods are commonly used

Normal Distribution Method

Log-Normal Distribution

Log-Plot Graphical Method


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Flood Frequency Analysis Method


Based on Assumption that events follow theshape of Standard Normal Distribution Curve


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Q

pro

bability

QTrMP KQQ

QP = Discharge Associated with Probability of Occurrence P

QM = Mean Discharge over the data set

Q = Standard Deviation of the Discharge data set

KTr = Frequency factor corresponding to Probability of Occurrence P


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Example of Peak Flood Estimation Flood

Example

Flood Frequency Analysis Normal Distribution Method

Actual

Year Year Max Flood Xi - Xavg (Xi - Xavg)2

Ranked Flow

(Decending

Order) Rank Probability Return Period

(No.) Q R P = R/n Tr = 1/P

(cumecs) (cumecs) (cumecs ) (yrs)

1970 1 26 2.9 8.3 48 1 0.04 24.001971 2 42 18.9 356.3 45 2 0.08 12.00

1972 3 17 -6.1 37.5 42 3 0.13 8.00

1973 4 35 11.9 141.0 35 4 0.17 6.00

1974 5 16 -7.1 50.8 35 5 0.21 4.80

1975 6 32 8.9 78.8 32 6 0.25 4.00

1976 7 48 24.9 618.8 26 7 0.29 3.43

1977 8 14 -9.1 83.3 25 8 0.33 3.00

1978 9 13 -10.1 102.5 23 9 0.38 2.671979 10 21 -2.1 4.5 21 10 0.42 2.40

1980 11 18 -5.1 26.3 21 11 0.46 2.18

1981 12 16 -7.1 50.8 20 12 0.50 2.00

f


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1982 13 20 -3.1 9.8 18 13 0.54 1.85

1983 14 15 -8.1 66.0 17 14 0.58 1.71

1984 15 35 11.9 141.0 17 15 0.63 1.60

1985 16 45 21.9 478.5 16 16 0.67 1.50

1986 17 23 -0.1 0.0 16 17 0.71 1.41

1987 18 14 -9.1 83.3 15 18 0.75 1.33

1988 19 12 -11.1 123.8 15 19 0.79 1.26

1989 20 17 -6.1 37.5 15 20 0.83 1.201990 21 25 1.9 3.5 14 21 0.88 1.14

1991 22 15 -8.1 66.0 14 22 0.92 1.09

1992 23 21 -2.1 4.5 13 23 0.96 1.04

1993 24 15 -8.1 66.0 12 24 1.00 1.00

Sample Pts = n = 24

Mean Qm = M 23.125

Sum of Squares = 2638.6

Variance = 114.72

Standard Deviation = 10.71

Coefficient of Variation = Cv = /M =0 . 4 6 3

Skewness Coefficient = SC = 3 Cv + Cv3

= 1.49

Input Return Period (Years) = Tr = 100 Input Value

Probability = p = 1/ Tr 0.01

Flood Estimate = Qt =

22)(

1

1xx

nS j

)1(

2

nV S

V

Actual

Year Year Max Flood Xi - Xavg (Xi - Xavg)2

Ranked Flow

(Decending

Order) Rank Probability Return Period

(No.) Q R P = R/n Tr = 1/P

(cumecs) (cumecs) (cumecs ) (yrs)

E l f P k Fl d E i i Fl d


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Input Return Period (Years) = Tr = 100 Input Value

Probability = p = 1/ Tr 0.01Flood Estimate = Qt =

w = 3.03485528

KTr= 2.32678649Flood Estimate = Qt =

Qt = 48.05 Cumecs

KtrQQmt

ww

wK

w

ww

Tr 32

2

001308.0189269.0532788.11

010328.0802853.051557.2

pw

2

1ln

L N l Di t ib ti M th d


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Log-Normal Distribution Method

Log Q or Ln Q

pro

bability

QTrMP KQQ lnlnln

lnQP = Log of Discharge Associated with Probability of Occurrence P

lnQM = Mean of Log Discharge over the data set

lnQ = Standard Deviation of the Log of Discharge data set

KTr = Frequency factor corresponding to Probability of Occurrence P

QP

= Antilog (ln QP

) = Discharge Associated with Probability of Occurrence P

Yields better Results

Compared to Normal

Distribution Method


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Log-Plot Method

Log Plot Discharge Vs Return Period

y = 12.724Ln(x) + 11.733

0

10

20

30

40

50

60

70

80

1 10 100Retun Period (Yrs)

Discharge

(cumecs)

Observed Discharge

Log. (Observed Discharge)

Trendline Equation is

Qt = 12.724 Ln(Tr) + 11.213

For Return Period Tr = 50 yrs

Qt = 12.724 Ln (50) + 11.213 = 61.0 cumecs

For Return Period Tr = 100 yrsQt = 12.724 Ln (100) + 11.213 = 69.8 cumecs

R ti l M th d f P k Fl d E ti ti


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Rational Method of Peak Flood Estimation

Attempts to give estimate of Design Discharge

taking into account: The Catchment Characteristics

Rainfall Intensity

Discharge Characteristics of the Catchment

AICQ T

Q = Design Discharge

IT = Average rainfall intensity (in/hr) for some recurrence interval, T

during that period of time equal to Tc.Tc = Time of Concentration

A = Area of the catchment in Sq. miles

C = Runoff coefficient; fraction of runoff, expressed as a

dimensionless decimal fraction, that appears as surface runoff

from the contributing drainage area.

R ti l M th d f P k Fl d E ti ti


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Rational Method of Peak Flood Estimation

Time of Concentration can be estimated using

Barnsby Williams Formula which is widely usedby US Highway Engineers

2.01.0

9.0

SA

LTc

L = Length of Stream in Miles

A = Area of the catchment in Sq. miles

S = Average grade from source to site in percent


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G t h i l St di


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Geotechnical Studies should provide the

following Information:

The types of Rocks, Dips, Faults and

Fissures

Subsoil Ground Water Level, Quality,

Artesian Conditions if any

Location and extent of soft layers

Identification of hard bearing strata

Physical properties of soil layers

G t h i l St di


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Example Geological Profile:

Cross section of the soil on the route of the Paris

The diagram above shows the crossing over the Seine via the Bir Hakeim

bridge and the limestone quarries under Trocadro

G t h i l St di


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Example: Cross section of the Kansas River, west of Silver Lake, Kansas

Typical Borehole

S i i C id ti


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Seismic Considerations

Source: Building Code of Pakistan

Tectonic Setting of the Bridge Site


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Tectonic Setting of the Bridge Site

Source: Geological Survey of Pakistan



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Impact on Following Features of Environment need toconsidered:

River Ecology which includes:

Marine Life

Wildlife along river banks

Riverbed Flora and fauna along river banks

Impact upon dwellings along the river if any

Impact upon urban environment if the bridge in an

urban area Possible impact upon archeological sites in vicinity

Bridge Economic Feasibility


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Bridge Economic Feasibility

Economic Analysis is Required at

Feasibility Stage to justify expenditure ofpublic or private funds

A Bridge is the most expensive part of a

road transportation network Types of Economic Analyses

Cost Benefit Ratio Analysis

Internal Rate of Return (IRR) Analysis

Bridge Economic Analysis/


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dge co o c a ys s/Life Cycle Cost Analysis (LCCA)

Time

CostsStre

am

BenefitsStream

C

onstruction

S

tage

Project LifeProjectStart

Da

te

P

rojectLife

E

nd

Date

Salv

age

Valu

e

Project Cost Benefit Analysis


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Project Cost Benefit Analysis

The objective of LCCA is to

Estimate the costs associated with the Project during Constructionan its service life. These include routine maintenance costs +Major Rehab Costs

Estimate the Benefits that will accrue from the Project includingtime savings to road users, benefits to business activities etc.

Bring down the costs and benefits to a common reference pt. in

time i.e. just prior to start of project (decision making time) Facilitate decision making about economic feasibility by

calculating quantifiable yardsticks such as Benefit to Cost Ratio(BCR) and Internal Rate of Return (IRR)

Note: Salvage Value may be taken as a Benefit

This includes cost of the Right-of-Way and substructure

What is Life Cycle Cost?


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What is Life Cycle Cost?

An economic analysis procedure that uses

engineering inputs

Compares competing alternatives

considering all significant costs

Expresses results in equivalent dollars

(present worth)

Time Period of Analysis


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Normally equal for all alternatives

Should include at least one major

rehabilitation

Needed to capture the true economicbenefit of each alternative

Bridge design today is based on a

probabilistic model of 100 years



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g yLife Cycle Cost Analysis (LCCA)

Time

Cos

tsStream

Be

nefitsStream

Construction

Stage Project LifeP

roject

StartDate

Project

Life

End

Date

S

alvage

V

alue

Costs and Benefits Change over the life of the Project

Amount of Money/Benefit accrued some time in future is worth less interms of Todays money

Same is the case with the benefits accrued over time

The Problem now is as to How to find the Worth of a Financial Amount inFuture in terms of Todays Money

This is accomplished by using the instrument of DISCOUNT RATE

Problem:



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g yLife Cycle Cost Analysis (LCCA)

DISCOUNT RATE:

The annual effective discount rate is the annual interest divided by the capitalincluding that interest, which is the interest rate divided by 100% plus theinterest rate. It is the annual discount factor to be applied to the future cashflow, to find the discount, subtracted from a future value to find the valueone year earlier.

For example, suppose there is an investment made of $95 and pays $100 in a

year's time. The discount rate according the given definition is:

%0.5100

95100

dRateDiscount

%26.59595100 iRateInterest

Interest Rate is calculated as $ 95 as Base

Interest Rate and Discount Rate are Related as Follows

2

1

ii

i

idRateDiscount

Discount Rate
http://en.wikipedia.org/wiki/Discount_factorhttp://en.wikipedia.org/wiki/Discount_factor


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Discount Rate Thus Discount Rate is that rate which can be

used to obtain the Present Value of Money that

is spent or collected in future

Net Present value of Cost incurred = Co = (1 - d)n CnIn Year n

Net Present value of Cost incurred = Bo = (1 - d)n BnIn Year n

Time

Costs

Stream

Benefits

Stream

Project

Life

Project

StartDate

Year nCn

Bn

Cost/ Benefit ProjectedBackward

Bo

Co

What Discount Rate to Use?


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What Discount Rate to Use? A first estimate of appropriate Discount

rate can be made as follows:

Estimate of

Discount Rate = Federal Bank Lending Rate Average Long-term Inflation Rate

Note: By subtracting the Inflation Rate in arriving at a Discount Rate theeffect of Inflation can be removed from consideration duringEconomic Analysis

The Discount Rate after subtracting the Inflation Rate is alsoReferred to as the Real Discount Rate

Govt. of Pakistan uses a Discount Rate of 6-7% for

economic analysis

Asian Development Bank uses a Discount rate of 12% forevaluation of projects

Discount Rate is less than the Real interest Rate as Governments

do not take a purely commercial view of an infrastructure project

Cost Considerations


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Cost Considerations

Maintenance andInspection

Cost

Initial Cost

Costs

Present Worth

Years

Rehabilitation Cost

Salvage

Value

Salvage

Costs

Cost Benefit Ratio


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Cost Benefit Ratio

Formula for Cost

Benefit Ratio

Benefit To Cost Ratio =

L

n

Ln

Cnd

Bnd

0

0

)1(

)1(

CostsofValuePresent

BenefitsofValuePresent

Where L = Life Span of the Project in Years

d = Discount Rate

Bn = Benefit in year nCn = Cost incurred in year n

Net Present Worth/ Value


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Net Present Worth/ Value

Net Present Worth/ Value = NPW or NPV

is defined as follows:

NPW = NPV = Present Value of Benefits Present Value of Costs

Note: If a Number of alternatives are being compared, the alternativethat has the highest Net Present Worth is the preferable one andwill also have the higher Benefit to Cost Ratio

What is Internal Rate of Return (IRR)


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What is Internal Rate of Return (IRR)

IRR may be defined as that Discount Rate

at which the Benefit to Cost Ratio (BCR) ofa Project becomes exactly 1.0

It is a better measure of economic viability

of a project compared to Benefit to CostRatio

It is a good indicator of how much inflation

increase and interest rate hike a projectcan tolerate and still be viable

Present Worth Factor


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Present Worth Factor

pwf = Present Worth Factor for discount rate d and year n

d = Discount rate

n = Number of year when the cost/ benefit will occur

ndpwf )1(

Present Worth Analysis


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Present Worth Analysis

Discounts all future costs and benefits to the present:

t=L

PW = FC + pwf [MC+IC+FRC+UC] + pwf [S]t=0

PW = Present Worth/ Value of the ProjectFC = First (Initial) Costt = Time Period of Analysis (ranges from 0 L)MC = Maintenance CostsIC = Inspection CostsFRC = Future Rehabilitation Costs

UC = Users CostsS = Salvage Values or Costspwf = Present Worth Factor



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Normally equal for all alternatives

Should include at least one major rehabilitation

Needed to capture the true economic benefit of each

alternative

Bridge design today is based on a probabilistic model of

100 years

Maintenance Costs


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Maintenance Costs

Annual cost associated with the upkeep of the

structure Information is difficult to obtain for a given

project

Cost varies on the basis of size of the structure

(sqft) Best Guess Values

Frequency - Annual

Concrete 0.05 % of Initial Cost

Structural Steel 0.05 % of Initial Cost


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Future Painting Costs


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Future Painting Costs

Only applies to structural steel structures but

excludes weathering steel Should occur every 20 years

Cost varies on the basis of size of the structure

(sqft) Best Guess Values

Frequency every 20 years

Concrete 0.0 % of Initial Cost



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Future Rehabilitation Costs

The frequency is not only a function of time but also thegrowing traffic volume and the structural beam system

Cost varies on the basis of size of the structure (sqft) andstructural beam system

Best Guess Values

Frequency

First occurrence Concrete 40 years

First occurrence Structural Steel 35 years

Annual traffic growth rate .75 % (shortens rehab

cycles) Concrete 20.0 % of Initial Cost


Salvage Value/Costs


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Salvage Value/Costs

Occurs once at end of life of structure

Difference between

Removal cost

Salvage value

Best Guess Values

Removal cost 10 % of Initial Cost

Salvage Value Concrete - 0 % of Initial Cost Salvage Value Structural Steel - 2 % of Initial Cost

Benefits from a Bridge


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Benefits from a Bridge

Monetizable Benefits

Time savings to road users

Growth in economic activity

Saving of Vehicular wear and tear

Reduction of accidents if applicable

Other Non-Monetizable Benefits Strategic Benefits

Documents

Lecture No. 1-A