Tuesday, December 27, 2016

METHODOLOGY FOR STRESSING OF PSC GIRDERS




UNCOILING OF H.T.STRANDS :

This operation is to be carried out on an elevated platform to prevent soiling of strands. The coil should be bound by pipes & couplers to ensure no sudden release of internal pressure in the coil. The strand shall be uncoiled layer by layer to prevent flying off of strands from the coil. Atmost caution shall be exercised while decoiling operations are in progress and no personnel/Labour shall be allowed to move in the area around the coil.
CUTTING OF STRANDS :

The uncoiled strands shall be laid on the elevated platform and cut to size as per the execution drawings. The cutting of strands shall be done only by abrasive cutter and no gas cutting shall be allowed. The length of the cable as given in the execution drawings shall be verified as to whether it includes the gripping length of 750mm on either side of the girder in case of both end stressing of cables is being done. For one end stressing 750mm extra on the stressing end & 250mm for dead end of the girder should be provided.
MAKING AND MARKING CABLES OUT OF CUT STRANDS :

The strands shall not be moved from the elevated platform till they are attached with tags bearing the specific cable nos. The cables shall be formed by tying the strands with binding wire at a distance centre to centre as necessary for the entire length of the cable.

FIXING OF GUIDE CONES :

The guide cone shall be fixed with the grout hole on the topside of the cone. The cable arrangement as per the drawing shall be maintained while fixing the cones. The sheathing shall be properly fixed into the mouth of the guide cone by properly turning the sheathing into the grooves meant for the purpose.

PROFILING OF SHEATHING :

The sheathing shall be profiled with the help of jigs. The jigs are to be prepared of 16mm dia reinforcement bars and shall be fixed @ 1000 mm c/c by tying firmly with the reinforcement. It is preferable to weld the supporting bars with reinforcement cage of the girder after the profiling of the cables is checked and approved.

THREADING OF STRANDS :

The cables prepared on the elevated platform shall be then brought to site carefully. The cable end tied with binding wire and then wrapped (at the tip) with PVC tapes shall be introduced into the duct from one end of the guide cone. Care shall be taken while threading the cables not to puncture the sheathing at any location.

CONCRETING OF GIRDER :

The girder may be cast with either pre threaded ducts or post threaded ducts.

a) Pre threaded:
The girder shall be concreted after the cables are introduced and strand ends are enclosed in gunny bags as protection. The cables shall be moved back and forth until concreting is completed to ensure free movement of strands. This will prevent any slurry from setting inside the sheathing and blocking the ducts. If there is a doubt of any blockage, the duct shall be flushed with water and subsequently with compressed air. Concrete cubes have to be taken (at least two sets per girder-set comprising of 6 cubes for the same batch) and marked to identify girder no. / Date of casting etc. During pouring of concrete care should be taken not to pour concrete directly on the tube units or the brusting reinforcements and careful observation should be made to ensure no pocket formation anywhere. Shutter vibrator and needle vibrator have to be operated properly.
b) Post threaded:
Provide a H.D.P.E. pipe of suitable diameter through the duct. During concreting this pipe is push back & forth to ensure no blockage in the duct. In this method threading is done just before pre stressing activity is taken up.
Before the stressing operations are undertaken following things have to be checked:

1. Check the correct functioning of jacks, Power pack pumps and leads.
2. Re-establish the modulus of elasticity of H. T. strands from the particular lot to be used from an approved laboratory. Re calculate and modify the elongation of strands, corresponding to the modulers of elasticity and section area for the particular lot of strand to be used for stressing.
3. Move the cables inside the duct to ensure pressure in the duct.
4. Clean the strands thoroughly to ensure no rusting on the strands in the gripping area at the permanent wedge location and master grip area to ensure this a length of strands protruding out from the face of the tube unit and length of 300mm inside the duct should be cleaned with wire brush and petrol to remove all the dirts, grease, oil etc. from the surface of the strands.
5. Wedges and bearing plates are inspected visually and cleaned thoroughly with Nylon wire brushing and petrol to remove all dirts, grease etc. from surface of the female parts of the bearing plates and serretions of wedges.
6. Wire brushing is not recommended for cleaning of wedges. We should use Nylon bristled brush.
THREADING OF BEARING PLATES AND JACKS:
On the attainment of strength of concrete as determined by cube crushing strength as specified by the consultant steps are taken to take up stressing.
Ø A tripod / stand or scaffolding is erected on each end of the girder to hang the prestressing jacks with the help of 3 to 5 Ton. chain pulley block in position. Height of scaffolding / tripod should be such to provide sufficient driving of the jack to thread the strands into the jack difficulties. Specific bearing plates duly cleaned are threaded with the strands.
Ø Cleaned Grips are threaded into the groove of the bearing plates.
Ø It is to be observed that strands in the area of gripping are cleaned.
STRESSING :
The power pack is supplied with 3 phase Power supply and it is connected to the jack. Now at both ends of the girder stressing is done simultaneously. The pressure is increased up to 50 kg/cm2 and halted. At this stage initial slackness is removed. Subsequently elongation at an interval of every 50 kg/cm2 is noted down. Zero correction is done and total elongation is calculated. Slip after 24 hours is also recorded by making a mark on the cable at 100 mm from the face of girder. The cables are cut from a distance of 50 mm from the wedges and grout cap is bolted.
SPECIAL NOTE DURING TRANSFER OF PRESTRESSING FORCE:

The transfer of the prestressing force shall be carried out gradually. Since sudden application of stress may result in severe eccentricities of Prestressing force in the concrete. This will also ensure transfer of prestress to the concrete is uniform along the length of the tension line.
CABLE AND STRESSING PREPARATION SHEET :
Before a cable is stressed, Cable and Stressing preparation sheet is updated. This sheet involves girder no., cable no., length of cable etc. Theoretical "E" value (assumed Young's modulus during design) and theoretical "A" value (assumed area of the cable during design) are entered into the sheet. Actual "E" and actual "A" value can be obtained from the strand manufacture's test certificate. Theoretical elongation & theoretical jacking force (obtained from the drawings) are updated. Jack efficiency and Jack ram area can be obtained from the Jack test certificates. Modified elongation and modified jacking force are computed as per the formulae given in the sheet. Finally jacking pressure is computed as per the modified elongation.

STRESSING READINGS SHEET:

While a cable is stressed the stress readings are entered into this sheet. From this total elongation is computed. The clients should authorize this sheet.The total tension imparted to each tendon shall conform to the design requirements and modified values based on the calculation. Initial slack in Prestressing tendons may be removed by applying small initial tension.
If the calculated elongation is reached before the specified gauge pressure, continue tensioning till attaining the specified gauge pressure provided the elongation does not exceed 1.05 times the calculated elongation. If 1.05 times the calculated elongation is reached before the specified gauge pressure is attained. Stop stressing and note the readings as per the charts.
If the calculated elongation has not reached at the specified gauge pressure, continue tensioning by intervals of 5kg/sqcm of gauge pressure until the calculated elongation is reached restricted to the upper limit of gauge pressure 1.05 times the specified gauge pressure.

LOCK OFF PRESSURE :
Lock of pressure should be in the order of 2/3rd of the stressing pressure. In case wedge set is found to be more than 6mm the lock off pressure may be increased by another maximum 10kg/cm2. In no case lock off pressure is more than 280kg/cm2. in case by increase of lock off pressure wedge sets did not improve. One has to take more care regarding cleaning of strands, wedges etc. before taking up the pre-stressing work.

TESTING OF JACKS AND PUMPS:
1. Interconnect the corresponding lines of both EOHP power pack and start one power pack to read corresponding gauge pressure on the others. If the gauge pressure are found to be same then go for the Jack test.
2. Put the jack face to face and fit the jack in line. Thread the strands of suitable length to grip on to the strands at the end of the jack. Give the initial movement to jack ram upto 50mm for both the jack and fix master grips on both jacks. The system is ready for efficiency test.
One Jack is first made active and increase the jack pressure @ intervals of 50Kg/sqcm and note the readings on the other jack pressure provide upto 85%of the U.T.S. of the strands work out the efficiency. Now the other jack is made active and former one is made passive and repeat the test and work out the efficiency. Average of these readings will give the efficiency of the jacks.
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Monday, November 28, 2016

What is difference between density & specific gravity?

Density is defined as amount of matter per unit volume. This means in a given space , how much mass or simply a matter occupy space.
Density is expressed by the formula

ρ = m/V where

ρ is the density
m is the mass
V is the volume

Specific Gravity is a dimensionless quantity. It is the ratio of density of the substance to the density of reference ( water ,air,petrol.. depends on our choice) substance.

Specific gravity is also called relative density and is expressed by the formula:

Specific Gravitysubstance = ρsubstance/ρreference

The reference material could be anything, but the most common reference is pure water.
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Relation of Mass and Weight

Mass and Weight

Mass and Weight - the Gravity Force

Mass and Weight are two often misused and misunderstood terms in mechanics and fluid mechanics.
The fundamental relation between mass and weight is defined by Newton's Second Law. Newton's Second Law can be expressed as
F = m a         (1)
where
F = force (N, lbf)
m = mass (kg, slugs)
a = acceleration (m/s2, ft/s2)

Mass

Mass is a measure of the amount of material in an object, being directly related to the number and type of atoms present in the object. Mass does not change with a body's position, movement or alteration of its shape, unless material is added or removed.
  • an object with mass 1 kg on earth would have the same mass of 1 kg on the moon
Mass is a fundamental property of an object, a numerical measure of its inertia and a fundamental measure of the amount of matter in the object.

Weight

weight - force and acceleration of gravity
Weight is the gravitational force acting on a body mass. The generic expression of Newton's Second Law (1) can be transformed to express weight as a force by replacing the acceleration - a - with the acceleration of gravity - g - as
Fg = m ag         (2)
where
Fg = gravitational force - or weight (N, lbf)
m = mass (kg, slugs)
ag = acceleration of gravity on earth (9.81 m/s2, 32.17405 ft/s2)

Example - The Weight of a Body on Earth vs. Moon

The acceleration of gravity on the moon is approximately 1/6 of the acceleration of gravity on the earth. The weight of a body with mass 1 kg on the earth can be calculated as
Fg_earth = (1 kg) (9.81 m/s2)
           = 9.81 N
The weight of the same body on the moon can be calculated as
Fg_moon = (1 kg) ((9.81 m/s2) / 6)
           = 1.64 N
The handling of mass and weight depends on the systems of units used. The most common unit systems are
  • the International System - SI
  • the British Gravitational System - BG
  • the English Engineering System - EE
One newton is
  • ≈ the weight of one hundred grams - 101.972 gf (gF) or 0.101972 kgf (kgF, kp)
  • ≈ halfway between one-fifth and one-fourth of a pound - 0.224809 lb or 3.59694 oz

The International System - SI

In the SI system the mass unit is the kg and since the weight is a force - the weight unit is the Newton (N). Equation (2) for a body with 1 kg mass can be expressed as:
Fg = (1 kg) (9.807 m/s2)
    = 9.807 (N)
where
9.807 m/s2 = standard gravity close to earth in the SI system
As a result:
  • a 9.807 N force acting on a body with 1 kg mass will give the body an acceleration of 9.807 m/s2
  • a body with mass of 1 kg weights 9.807 N

The Imperial British Gravitational System - BG

The British Gravitational System (Imperial System) of units is used by engineers in the English-speaking world with the same relation to the foot - pound - second system as the meter - kilogram - force second system (SI) has to the meter - kilogram - second system. For engineers who deals with forces, instead of masses, it's convenient to use a system that has as its base units length, time, and force, instead of length, time and mass.
The three base units in the Imperial system are the foot, the second, and the pound-force.
In the BG system the mass unit is the slug and is defined from the Newton's Second Law (1). The unit of mass, the slug, is derived from the pound-force by defining it as the mass that will accelerate at 1 foot per second per second when a 1 pound-force acts upon it:
1 lbf = (1 slug)(1 ft/s2)
In other words, 1 lbf (pound-force) acting on 1 slug mass will give the mass an acceleration of 1 ft/s2.
The weight of the mass from equation (2) in BG units can be expressed as:
Fg (lbf) = m (slugs) ag (ft/s2)
With standard gravity - ag = 32.17405 ft/s2 - the mass of 1 slug weights 32.17405 lbf (pound-force).

The English Engineering System - EE

In the English Engineering system of units the primary dimensions are are force, mass, length, time and temperature. The units for force and mass are defined independently
  • the basic unit of mass is pound-mass (lbm)
  • the unit of force is the pound (lb) alternatively pound-force (lbf).
In the EE system 1 lb of force will give a mass of 1 lbm a standard acceleration of 32.17405 ft/s2.
Since the EE system operates with these units of force and mass, the Newton's Second Law can be modified to
F = m a / gc         (3)
where
gc = a proportionality constant
or transformed to weight
Fg = m ag / gc         (4)
The proportionality constant gc makes it possible to define suitable units for force and mass. We can transform (4) to
1 lbf = (1 lbm) (32.174 ft/s2) / gc
or
gc = (1 lbm) (32.174 ft/s2) / (1 lbf)
Since 1 lbf gives a mass of 1 lbm an acceleration of 32.17405 ft/s2 and a mass of 1 slug an acceleration of 1 ft/s2, then
1 slug = 32.17405 lbm

Example - Weight versus Mass

The mass of a car is 1644 kg. The weight can be calculated:
Fg = (1644 kg) (9.807 m/s2)
    = 16122.7 N
    = 16.1 kN
- there is a force (weight) of 16.1 kN between the car and the earth.
  • 1 kg gravitation force = 9.81 N = 2.20462 lbf

Related Topics

  • Basics - The SI-system, unit converters, physical constants, drawing scales and more
  • Fluid Mechanics - The study of fluids - liquids and gases. Involves velocity, pressure, density and temperature as functions of space and time
  • Mechanics - Forces, acceleration, displacement, vectors, motion, momentum, energy of objects and more
  • Statics - Loads - force and torque, beams and columns

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Density, Specific Weight and Specific Gravity

An introduction to density, specific weight and specific gravity - formulas with examples

Density

Density is defined as mass per unit volume. Mass is a property.
Density can be expressed as
ρ = m / V
   = 1 / ν         (1)
where
ρ = density (kg/m3, slugs/ft3)
m = mass (kg, slugs)
V = volume (m3, ft3)
ν = specific volume (m3/kg, ft3/slug)
The SI units for density are kg/m3 - the Imperial (U.S.) units are slugs/ft3.
Pounds per cubic foot - lb/ft3 - is often used as a measure of density in the US, but pounds are really a measure of force, not mass. Slugs are the correct measure of mass. You can multiply slugs by 32.2 for a rough value in pounds (lbm).
On atomic level - particles are packed tighter inside a substance with higher density. Density is a physical property - constant at a given temperature and pressure - and may helpful for identification of substances.

Example - Density of a Golf ball

A golf ball has a diameter of 42 mm and a mass of 45 g. The volume of the golf ball can be calculated as
V = (4 / 3) π ((42 mm) (0.001 m/mm) / 2)3
   = 3.8 10-5 m3
The density of the golf ball can then be calculated as
ρ = (45 g) (0.001 kg/g) / (3.8 10-5 m3)
   = 1184 kg/m3

Example - Using Density to Identify a Material

An unknown liquid substance has a mass of 18.5 g and occupies a volume of 23.4 ml (milliliter).
The density of the substance can be calculated as
ρ = [(18.5 g) / (1000 g/kg)] / [(23.4 ml) / (1000 ml/l) (1000 l/m3)]
    = (18.5 10-3 kg) / (23.4 10-6 m3)
    = 790 (kg/m3)
If we look up densities of some common liquids, we find that ethyl alcohol - or ethanol - has a density of 789 kg/m3. The liquid may be ethyl alcohol!

Example - Density to Calculate Volume Mass

The density of titanium is 4507 kg/m3. The mass of 0.17 m3 volume titanium can be calculated as
m = (0.17 m3) (4507 kg/m3)
    = 766.2 (kg)
Note! - be aware that there is a difference between "bulk density" and actual "solid or material density". This may not be clear in the description of products. Always double check values with other sources before important calculations.

Specific Weight

Specific Weight is defined as weight per unit volume. Weight is a force.
Specific Weight (or force per unit volume) can be expressed as
γ = ρ ag         (2)
where
γ = specific weight (N/m3, lb/ft3)
ρ = density (kg/m3, slugs/ft3)
ag = acceleration of gravity (9.807 m/s2, 32.174 ft/s2)
The SI units for specific weight are N/m3. The imperial units are lb/ft3.
Local acceleration of gravity - ag - is (under normal conditions) 9.807 m/s2 in SI units and 32.174 ft/s2 in imperial units.

Example - Specific Weight of Water

The density of water is 1000 kg/m3 at 4 oC (39 oF). The specific weight in SI units is
γ = (1000 kg/m3) (9.81 m/s2)
    = 9810 (N/m3)
    = 9.81 (kN/m3)
The density of water is 1.940 slugs/ft3 at 39 oF (4 oC). The specific weight in Imperial units is
γ = (1.940 slugs/ft3) (32.174 ft/s2)
    = 62.4 (lb/ft3)

Specific Weight for Some common Materials

ProductSpecific Weight
- γ -
Imperial Units
(lb/ft3)		SI Units
(kN/m3)
Aluminum 172 27
Brass 540 84.5
Carbon tetrachloride 99.4 15.6
Copper 570 89
Ethyl Alcohol 49.3 7.74
Gasoline 42.5 6.67
Glycerin 78.6 12.4
Kerosene 50 7.9
Mercury 847 133.7
SAE 20 Motor Oil 57 8.95
Seawater 63.9 10.03
Stainless Steel 499 - 512 78 - 80
Water 62.4 9.81
Wrought Iron 474 - 499 74 - 78

Specific Gravity (Relative Density)

Specific Gravity - SG - is a dimensionless unit defined as the ratio of the density of a substance to the density of water - at a specified temperature and can be expressed as
SG = ρsubstance / ρH2O         (3)
where
SG = Specific Gravity of the substance
ρsubstance = density of the fluid or substance (kg/m3)
ρH2O = density of water - normally at temperature 4 oC (kg/m3)
It is common to use the density of water at 4 oC (39oF) as a reference since water at this point has its highest density of 1000 kg/m3 or 1.940 slugs/ft3.
Specific Gravity - SG -  is dimensionless and has the same value in the SI system and the imperial English system (BG). SG of a fluid has the same numerical value as its density expressed in g/mL or Mg/m3. Water is normally also used as reference when calculating the specific gravity for solids.
  • Thermal Properties of Water - Density, Freezing temperature, Boiling temperature, Latent heat of melting, Latent heat of evaporation, Critical temperature ...

Specific Gravity for some common Materials

SubstanceSpecific Gravity
- SG -
Acetylene 0.0017
Air, dry 0.0013
Alcohol 0.82
Aluminum 2.72
Brass 8.48
Cadmium 8.57
Chromium 7.03
Copper 8.79
Carbon dioxide 0.00198
Carbon monoxide 0.00126
Cast iron 7.20
Hydrogen 0.00009
Lead 11.35
Mercury 13.59
Nickel 8.73
Nitrogen 0.00125
Nylon 1.12
Oxygen 0.00143
Paraffin 0.80
Petrol 0.72
PVC 1.36
Rubber 0.96
Steel 7.82
Tin 7.28
Zinc 7.12
Water (4oC) 1.00
Water, sea 1.027

Example - Specific Gravity of Iron

The density of iron is 7850 kg/m3. The specific gravity of iron related to water with density 1000 kg/m3 is
SG = (7850 kg/m3) / (1000 kg/m3)
    = 7.85

Specific Gravity for Gases

The Specific Gravity of a gas is normally calculated with reference to air - and defined as the ratio of the density of the gas to the density of the air - at a specified temperature and pressure.
The Specific Gravity can be calculated as
SG = ρgas / ρair         (3)
where
SG = specific gravity of gas
ρgas = density of gas (kg/m3)
ρair = density of air (normally at NTP - 1.205 kg/m3)
Molecular weights can be used to calculate Specific Gravity if the densities of the gas and the air are evaluated at the same pressure and temperature.

Related Topics

  • Basics - The SI-system, unit converters, physical constants, drawing scales and more
  • Fluid Mechanics - The study of fluids - liquids and gases. Involves velocity, pressure, density and temperature as functions of space and time
  • Mechanics - Forces, acceleration, displacement, vectors, motion, momentum, energy of objects and more
  • Beams and Columns - Deflection and stress, moment of inertia, section modulus and technical information of beams and columns
  • Material Properties - Material properties for gases, fluids and solids - densities, specific heats, viscosities and more
  • Statics - Loads - force and torque, beams and columns
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Density Test Useing Hydrometer

https://youtu.be/GTvmYaQq6Mc
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Sunday, November 27, 2016

MAPPING METHODS IN SURVEYING

The aim of surveying is to make plans and maps to show various objects on the ground at their relative position to suitable scale. Various steps involved in making the plans is explained below.
map_survey

Mapping Methods in surveying:

After completing field work in chain survey and compass survey lot of office work is involved to prepare the plan (map) of the area surveyed. In plane table survey office work is less. The office work involved consist of:
1. Applying necessary corrections to measurements
2. Drawing index plan
3. Selecting scale
4. Selecting orientation
5. Drawing network of survey lines
6. Distributing closing error
7. Filling in the details
8. Colouring the map
9. Drawing graphical scale
10. Writing index.

1. Applying Necessary Corrections to Measurements

Necessary tape and chain corrections and corrections for local attraction in case of compass survey, should be applied to the survey lines measured.

2. Drawing Index Plan

On a rough sheet index plan also known as key plan is drawn. This need not be to the scale but distances and directions of network of survey lines should be approximately to a scale. This plan is necessary to identify the shape of the area to be plotted.

3. Selecting Scale

Depending upon the type of survey, scale should be selected. In general, scale selected should be as large as possible, if a range of scale is recommended. It depends upon the size of the paper as well as largest linear measurement in the field.

4. Selecting Orientation

Looking at index plan, orientation of map is to be decided so that the map is placed in the middle of the drawing sheet with its larger dimension approximately along the length of paper. North direction is selected and marked.

5. Drawing Network of Survey Lines

Studying index map and orientation of paper, first station point of survey is marked. Starting from here one by one survey line is drawn to the scale in its direction. After drawing all survey lines, it is clearly seen whether the selected scale and orientation appropriate. If necessary they may be changed and network of survey lines is redrawn.

6. Distributing Closing Error

Sometimes in closed traverse, the last point may not coincide with the plotted position of first point. The difference between the plotted position is known as closing error. Before adjusting closing error it is necessary that there are no plotting errors. If it is due to field work error and the error is reasonably small it can be adjusted in the office. If error is large, one has to go back to the field and check doubtful measurements. In the office closing error is adjusted distributing it suitably to all lines graphically or by mathematical calculation of corrected coordinates of station points. After adjusting closing error network of survey lines are drawn as per the convention.

7. Filling in the Details

Surveyor has to go through details of one by one survey lines. One by one point of object noted in the field is marked on the drawing sheet by converting the change and offsets to the scale. Main scale and offset scales will be quite useful for this work. After marking the salient points of the objects like building, boundary lines, roads, culvert ends, trees, electric poles etc. the respective lines are joined to mark the object. The field book will be useful in identifying the objects. If the object is building, the measurements may be only for salient points near the survey lines looking at overall dimensions of the building and scaling down, complete building may be shown in the plan. Thus attending to the field observations of each survey lines all details may be shown. Standard conventions should be used in showing the objects.

8. Colouring the Map

If coloured maps are to be made, the recommended light washes of standard shades as listed is IS 962- 1989 may be applied.

9. Drawing Graphical Scale

As the drawing sheet may shrink and the measurement taken from shrunk sheet may mislead the distances between any two objects on the map, it is necessary to draw a graphical scale of 150 to 270 mm long just over the space for indexing the drawing, which is right hand side lower corner of the sheet.

10. Writing Index

Index is the details giving the description of the area plotted, scale used, name of leader of survey party and the person drawing the plan/map. etc. It is normally written in the right hand side lower corner of the drawing sheet. North direction is shown neatly at the right hand side top corner.

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LEARN SURVEYING – TOTAL STATION EQUIPMENT

Total Station is a modern surverying equipment used by civil engineers and surveying engineers at field for various applications such as distance measurement, slope and angle measurements. All the measurement data is displayed and stored in this equipment.
This instrument replaces the old theodolotie which involved manual calculations and time consuming surveying. The onboard computer in this equipment can automatically use measured data to compute horizontal and vertical angles, distance etc. in realtime avoiding manual calculations.The data in total station can be exported to another computer for analysis, mapping of surveyed area with ease.
Unfortunately, Indian Univerties still use old theodolite for surveying classes. So, this is the high time to learn and gain skills on recent trends in surveying. Civil Simplified has come up with a solution to provide practical training to civil engineers and surveying engineers during this winter. Following is a message from Civil Simplified team regarding their program. You can directly contact them for more information on the program.
LEARN SURVEYING USING INDUSTRY-PREFERRED TOTAL STATION EQUIPMENT!
A unique opportunity to work on a Surveying project using Total Station
Civil Simplified- Total Station Surveying
Dear Civil Engineering students,
To be a successful Civil Engineering professional, you need practice that will help you acquire the skills important for professional success. These skills will add weight to your resume which in turn helps improve your employability.
And this upcoming winter holiday break is the perfect occasion to develop these practical skills. Civil Simplified, brainchild of IIT Kanpur alumni, has conceived Winter Training and Internship Programs that will help improve your practical skills in Civil engineering disciplines.
If you want to make a career in Surveying, then practical knowledge of using Total Station surveying equipment is necessary. Total Station is commonly preferred surveying equipment in Civil engineering industries. In the winter training camp in Total Station, you will perform a full-scale survey of an area span using Total Station. You will also analyze the surveyed data using Geographic Information Systems (GIS) – the same technology that drives GPS systems.
Civil Simplified Winter Training and Internship programs also include courses in Structural e
ngineering, Geotechnical engineering, Transportation engineering, and GIS. You can visit Civil Simplified for more details.
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Monday, November 7, 2016

Los Angels Abrasion test for Aggregate

https://www.youtube.com/watch?v=g2ZCI5qBat0
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Detarmination of Aggregate impact value test

https://www.youtube.com/watch?v=Mn7aeorMpTs
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Sunday, November 6, 2016

Flakiness and Elongation test

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Flakiness index and Elongation Index of Coarse Aggregates
i.             to determine the elongation index of the given aggregates

ii.            to determine the flakiness index of the given aggregates


APPARATUS:
The apparatus for the shape tests consists of the following:

(i)   A standard thickness gauge

        (ii)  A standard length gauge    

(iii) IS sieves of sizes 63, 50 40, 31.5, 25, 20, 16, 12.5,10 and 6.3mm

(iv)       A balance of capacity 5kg, readable and accurate up to 1 gm.


THEORY:

       The particle shape of aggregates is determined by the percentages of flaky and elongated particles contained in it. For base course and construction of bituminous and cement concrete types, the presence of flaky and elongated particles are considered undesirable as these cause inherent weakness with possibilities of breaking down under heavy loads. Thus, evaluation of shape of the particles, particularly with reference to flakiness and elongation is necessary.

       The Flakiness index of aggregates is the percentage by weight of particles whose least dimension (thickness) is less than three- fifths (0.6times) of their mean dimension. This test is not applicable to sizes smaller than 6.3mm.

       The Elongation index of an aggregate is the percentage by weight of particles whose greatest dimension (length) is greater than nine-fifths (1.8times) their mean dimension. This test is not applicable for sizes smaller than 6.3mm.


PROCEDURE:

   

i)  Sieve the sample through the IS sieves (as specified in the table).

ii)Take a minimum of 200 pieces of each fraction to be tested and weigh them.

         (iii)    In order to separate the flaky materials, gauge each fraction for thickness on a thickness gauge. The width of the slot used should be of the dimensions specified in column (4) of the table for the appropriate size of the material.

(iv)   Weigh the flaky material passing the gauge to an accuracy of at least 0.1 per cent of the test sample.

         (v)    In order to separate the elongated materials, gauge each fraction for length on a length gauge. The width of the slot used should be of the dimensions specified in column (6) of the table for the appropriate size of the material.

         (vi)   Weigh the elongated material retained on the gauge to an accuracy of at least 0.1 per cent of the test sample.


Size of aggregates
Weight of
fraction
consisting
of at least
200 pieces,g
Thickness gauge size, mm
Weight of aggregates in each fraction passing thickness gauge,mm
Length gauge size, mm
Weight of aggregates in each fraction retained on length gauge,mm
Passing through IS Sieve, mm
Retained on IS Sieve,

mm
1
2
3
4
5
6
7
63
50
W1
23.90
X1
–
–
50
40
W2
27.00
X2
81.00
Y1
40
31.5
W3
19.50
X3
58.00
Y2
31.5
25
W4
16.95
X4
–
–
25
20
W5
13.50
X5
40.5
Y3
20
16
W6
10.80
X6
32.4
Y4
16
12.5
W7
8.55
X7
25.5
Y5
12.5
10
W8
6.75
X8
20.2
Y6
10
6.3
W9
4.89
X9
14.7
Y7
Total
W =

X =
Y =


OBSERVATIONS:
              Flakiness Index     =    (X1+ X2+…..) / (W1 + W2 + ….) X 100

              Elongation Index   =     (Y1 + Y2 + …) / (W1 + W2 + ….) X 100     

RESULT:

i)   Flakiness Index     =   

ii)  Elongation Index   =

RECOMMENDED VALUE:

               The shape tests give only a rough idea of the relative shapes of aggregates. Flaky and elongated particles should be avoided in pavement construction, particularly in surface course. If such particles are present in appreciable proportions, the strength of pavement layer would be adversely affected due to possibility of breaking under loads. Workability is reduced for cement concrete. IRC recommendations for maximum limits of flakiness index  are as given.


Sl No:
Type of pavement
Maximum limits of flakiness index, %
   1
Bituminous carpet
30
   2 (i)
Bituminous / Asphaltic concrete
25
   (ii)
Bituminous Penetration  macadam
    (iii)
Bituminous surface dressing (single coat, two coats & precoated)
   (iv)
Built up spray grout
   3 (i)
Bituminous macadam
15
   (ii)
WBM base course and surface course

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