Seminar report

On

“MANUFACTURE OF PRE STRESSED TUBULAR SPUN CONCRETE POLE OF 11 METRE LONG”

SUBMITTEDTO

VIVESWARAIAH TECHNOLOGICAL UNIVERSITYBELGAUM

FOR THE PARTIAL FULFILLMENT OF M-TECH (STRUCTURAL ENGINEERING)

BY ASLAM KHAN

Reg. No: -1st Semester M-Tech Structures

Under The Guidance of: G.A.SATISH Senior lecturer

Department of Civil Engineering

BANGALORE INSTITUTE OF TECHNOLOGY(Affiliated To Visveswaraiah Technological University)

Bangalore-560004

BANGALORE INSTITUTE OF TECHNOLOGYBANGALORE -560004

CERTIFICATE

This is to certify that Mr. ASLAM KHAN bearing university USN has submitted the seminar report on “MANUFACTURE OF PRE STRESSED TUBULAR SPUN CONCRETE POLE OF 11 METRE LONG” in partial fulfillment of the 1st semester M-Tech course in structural engineering as prescribed by the Visveswaraiah Technological University during the academic year 2006-2007, under the guidance of senior lecturer G.A.SATISH

Prof.K.JAYRAM G.A.SATISH H.O.D civil engg department. Senior lecturer

Department of Civil Engineering

ACKNOWLEDGEMENT

I express my deep sense of gratitude to senior lecturer G.A.SATISH, Department of Civil Engineering, BIT, for his guidance and help through out this seminar work.

I will remain thankful to all the faculty members of Department of Civil Engineering, BIT for their support during the course of this work.

Finally I express gratitude to my parents, fellow students and friends.

ASLAM KHAN M-TECH STRUCTURES

BANGALORE INSTITUTE OF TECHNOLOGY

CONTENTS

Page NoACKNOWLEDGEMENT

ABSTRACT

1. About Industry 1

2. Manufacture of Prestressed Spun Concrete Pole Of 11 Meter length 2

3. Technical specifications for Poles 4

4. Manufacturing process of Poles 11

5. Time study 15

6. Conclusions 16

7. Time Study report 17

8. Annexure

ABSTRACT

The report contains detail information of manufacturing of pre stress tubular spun concrete pole.

The manufacturing industry namely FERRO CEMENT PRE FAB LTD situated at 14-c Attibele industrial area Bangalore.

The product manufactured in the industry involved chain line production with movement of crane all safety measures were incorporated and employees were thoroughly briefed about the safety aspect to be followed during manufacturing process.

Special emphasis was given to time study of manufacture of the pre stressed tubular pole.

1. ABOUT THE INDUSTRY

Ferro cements Pre Fab Ltd is situated at 14-C Attibele Industrial Area Bangalore.

The company manufactures the following

1. Pre stressed Tubular spun concrete poles of 11 meter long.

2. Ferro cement sump tanks and septic tanks

3. Pre fabricated Ferro cement community Toilet Blocks.

4. Pre tensioned undulated trough section

5. Ferro cement slabs of ordered sizes.

The company possess in house fabrication workshop to prepare state of art molds and other

fabrication work.

The following machinery are available in the factory

1. A moving overhead crane of 10ton capacity.

2. A concrete batch mixing plant.

3. Small capacity concrete mixers.

4. Molds of different capacities

5. A boiler for steam producing

6. A wire-cutting machine.

7. A bar bending machine.

8. A compression-testing machine of 200ton capacity.

9. Sieve shaker, drying oven, sieves and other testing equipment.

10. Motor for spinning.

The company’s organization consists of managing director at the top management production

engineers at the middle management and skilled labour with supervisors. The manpower capacity

of the company including casual labour is 58. The company works in day and night shifts.

2. MANUFACTURE OF PRE STRESSED TUBULAR SPUN CONCRETE POLE OF 11 METER LONG.

INTRODUCTION:

Wooden, steel and concrete poles were used for power distribution lines since 19 th century.

The first poles used were wooden poles. When demand for poles increase and as the power lines

under construction required longer poles suitable for resisting larger horizontal forces, steel poles

were introduced in substitution towood.

Though both materials are still in use through out the world, with wood primarily used for

short length small forces country lines the general trend is to substitute both the materials with

concrete and Use reinforced and prestressed concrete poles instead.

Wooden have limited life and steel poles have a longer life compared to wooden poles requires continuous maintenance for protection against corrosion concrete and particularly prestressed concrete poles can be considered as having an unlimited life without maintenance cost for their corrosion protection. Poles supporting power lines are subjected to relatively small vertical forces and Primarily to large horizontal forces at bottom. The horizontal forces at their top are smaller along the axis of the power line and much larger on direction perpendicular to it. As in the perpendicular direction the pole must resist the horizontal forces caused from wind loads against the poles and the wires carried by them.

In view of the difference in the horizontal forces to which a pole is subjected, the original

solution given and, still adopted by authorities is to give the pole a cross section with larger

moment in one direction and smaller one in the direction perpendicular to it like example a

rectangular or double T cross section. Experience however has shown that concrete poles with a

circular cross section are preferable to poles with rectangular or T section as they resist better

impact loads and little extra cost give the added advantage that they have an equal resistance to

horizontal forces in all direction. The circular cross section besides the advantage mentioned

earlier lends it self to very well to use for the manufacture of poles of the spinning process. As well

known the spinning process is one of the best methods of casting freshly cast concrete, as the

centrifugal forces applied to concrete, secure a dense, excellent quality concrete at relatively less

manufacturing costs. The pre stressed hollow or tubular pole have proved to be more economical,

easily transported and erected due to lightweight.

Prestressed Tubular Spun Concrete Poles of 11 meter long were manufactured to BESCOM

against their order.

3. TECHINACAL SPECIFICATION FOR SPUN CONCRETE POLES

3.1 SCOPE: This specification covers design, manufacture, testing and supply of pre stressed

concrete tubular spun poles designed for a working load of 500Kg.

3.2 APPLICABLE STANDARDS: The poles shall comply the provisions made in the following

IS specification except when the conflict with specific requirements in this specification

a) IS 1678-1978 Specification for stressed concrete poles overhead power, traction and

telecommunication lines.

b) IS 2905-1966-Methods of test for concrete poles for overhead power and telecommunication

lines

c) IS 7321-1974 –Code of practice for selection handling and errection of concrete poles for

overhead power and telecommunication lines.

d) IS- 13158-1991 –Prestressed concrete circular spun poles for overhead power lines.

3.3 TERMINOLOGY:

For the purpose of this specification the definitions of average, permanent load, load factor,

transverse load at first crack, ultimate failure, ultimate transverse load and working load shall be as

per IS 1678 or any other equivalent International standards.

3.4 DIMENSIONS AND SHAPE:

The poles shall be of hollow and circular in shape with an outside taper of 1:75. The diameter

and thickness shall be as per design requirements. The tolerances shall be as follows:

Outer diameter +4mm -2mm

Length +50mm -10mm

3.5 CEMENT:

3.5.1. High strength ordinary Portland cement confirming to IS 269-1976 or Rapid hardening

cement confirming to IS 804-1978 or any other cement of equivalent to International Standard

shall be used which shall have the following additional requirements:

Initial Setting Time: Not less than 30minutes

Final Setting Time: Not more than 600minutes

3.5.2. The minimum compressive strength of standard mortar cube with standard sand as per IS650

at 7 days shall be 375kgs/cmsqare.

A minimum 3 trail cubes shall be made with aggregate grading to be used for the approved

mix and the average compressive results at 7 days shall be determined to asses the suitability of the

cement for each and every batch of cement.

3.6 AGGREGATES:

Coarse aggregates and fine aggregates for casting of pole shall confirm to IS 383 or any other

equivalent International standard. The normal maximum size of aggregates shall in no case more

than 20mm or 1/4 th the minimum thickness of the pole whichever is less than the spacing between

the prestressing wires.

Each size of the graded aggregate shall be stocked in different storage bins or stock piles and

shall be mixed only after the quantity required for each size has been separately weighed .The

storage bins or stock piles shall be under cover to protect from weather.

3.7 WATER:

Water should be free from chlorides, sulphates other salts and organic matter. Potable water

will be generally suitable.

3.8 ADMIXTURES:

Admixtures should not contain calcium chloride or other chlorides and salts which are likely

to promote corrosion in steel.

3.9 REINFORCEMENT:

3.9.1. Reinforcing steel bars and wires used for the manufacture of prestressed pole shall confirm

to the following Indian Standards or any other equivalent International Standards.

a. IS: 1785(Part-I) Specification for plain hard drawn steel wire for prestressed

concrete Part-I cold drawn stress relieved wire (second revision)

b. IS: 1785(Part-II)-1983 Specification for plain hard drawn steel wire for

prestressed concrete Part –II as drawn wire (First revision).

c. IS: 2090-1983 Specification for high tensile steel bars used in PSC.

d. IS-6003: 1983 Specification for indented wire for PSC(First revision).

3.9.2. The surface of all reinforcement shall be free from loose scale, oil grease, clay or any other

material that may have deterioting effect on the bond between the reinforcement and concrete.

3.10 CONCRETE:

The concrete mix shall be designed to the requirement laid down for controlled concrete

(also called design mix concrete) in IS 1343 and IS-456or any other equivalent International

Standards subjected to the following conditions:

a) Minimum cube strength at 28 days should be at least 50N/mm2.

b) The concrete strength at least half the 28day strength ensured in the design strength.

3.11 MOULDS:

Moulds shall be of steel and or rigid construction to prevent distortion and so arranged as to

provide smooth surface. The moulds shall not allow any leakage of cement grout during casting.

The holes in the end pates for HT wire shall be accurately drilled by jigs to ensure

interchangeability. The end plate is designed to withstand forces arising out of the change in

direction of prestressing wires during tensioning.

3.12 TENSIONING OF WIRES:

3.12.1. The HT wires shall be placed axially at regular spacing along the circumference. The

spacing shall as per IS-1678 or any other equivalent International Standard. While cutting of HT

wires automatic machines is be used. Button heading and forming reinforcement cages shall be

done manually.

3.12.2. Helical steel shall be of 2.7mm dia MS wires pitch shall be of 150mm.

3.12.3. The clear cover shall be of 20mm.

3.12.4. Pre tensioning shall be by automatic machines. Force shall be applied for the entire group

of HT wires to ensure all wires are equally stressed.

3.12.5. The pre stressing wires shall be stretched by an approved method. The anchoring of the

stretched wires shall be such that during manufacture and until the wires are released, no slippage

occurs. The force at the time of initial stretching shall addition to imparting of designed prestress

also be sufficient to over come the friction on account of any change in the inclination of wires and

slippage might occur during the anchoring process which will have to be suitably compensated

3.12.6. The tensioning of the prestressing wires shall be carried out in a manner that will induce a

smooth and even rate increase of stress in the wires.

3.12.7. The force induced in the pre stressing wires shall be determined by means of gauges

attached to the pretensioning apparatus and cross checked by extension to be achieved shall be

determined well in advance, based on trails conducted on representative samples of wires as used

in the pole. The accuracy of the devices for measuring of the tension force shall be within plus or

minus 5%.

3.13 MIXING AND CONSOLIDATION OF CONCRETE:

3.13.1. Provision shall be made to measure the quantities of cement and fine and coarse aggregate

by weight only. The accuracy of the measuring equipment shall be plus or minus 3%. All the

measuring equipment shall maintained in clean and serviceable condition and accuracy regurly.

Modern highspeed mixers, preferably pan or turbine type shall be used for mixing concrete.

3.13.2. The manufacture of poles shall be done under suitable cover and not in open.

3.13.3. The concrete shall be thoroughly mixed and consolidated.

3.13.4. Freshly cast poles shall protected during the first stage of hardening from harmful sunshine,

dry winds, cold and rain.

3.14 DETENSIONING OF WIRES:

3.14.1. Anchoring system shall provide a device for gradual detensioning of the wires. No back

pulling of the wires shall be permitted in gradual de tensioning device. Flame cutting of wires

before release of full tension shall be strictly prohibited.

3.14.2. The transfer of prestress shall not beeffected until the concrete in the poles has attained

specified strength as established of the cube tests.

3.15 CURING:

3.15.1 The curing shall be done on a saturated steam at 65degrees centigrade. Ensure that 80% of

strength is reached in 6 hours. There after wires will be cut demoulded and transferred to water for

14 days curing.

3.15.2 During manufacture periodical tests on concrete cubes of hallow cylindrical specimen

measuring 200mm dia and 300mm height shall carried out till the concrete achieves the require

strength at transfer. There after test on concrete shall be carried out as per IS 1343.

3.16 EARTHING:

3.16.1. Earthing shall be provided by having a length of 8SWG GI wire embedded in concrete

during manufacture and ends of the wires left projecting from the pole to a length of 100mm at

250mm from top and 150mm below ground level.

3.16.2 Earth wire shall not be allowed to come in contact with the pre stressing wire.

3.17. FINISH:

3.17.1. Poles shall be free from surface defects including hair cracks. The surface of the pole in

contact with the steel mould shall be smooth and regular in shape and shall as for as possible be

free from pores. Water retaining pockets and honeycombing formation shall not be admissible.

25mm thick 1:2 cement mortar cover shall be provided on the full area of the top of pole.

3.17.2. The ends of the pre stressing wires shall be cut as close to surface of the pole as possible

and in any case shall not project more than 3mm.

3.17.3. The ends of pre stressing wires shall be given two coats of suitable anti corrosive paints

approved by BESCOM.

3.17.4. No touching up or finishing by cement grout shall be done on the poles after it is removed

from the mould.

3.17.5. Metallic base plate is to be provided at the bottom of the pole.

3.18.WELDING AND LAPPING OF STEEL:

The high tensile steel wire shall be continuous over the entire length of the tendon. Welding

shall not be allowed in any case.

3. 19.PROVISION OF HOOKS AND HOLES:

3.19.1.Though holes shall be provided for fixing cross arms and clamp as specified by BESCOM.

3.19.2.A set of step up bolts shall be supplied along with each lot of 100 poles.3.20.TESTS:

3.20.1 During manufacture tests on concrete shall be carried out as detailed in this specification.

3.20.2 Transverse strength test: Poles made of ordinary Portland cement shall be tested on

completion of 28 days and poles made of rapid hardening cement only on completion of 14 days

after the day of manufacture.

3.20.3 The pole may be tested in either horizontal or vertical position. If tested on horizontal

position provision may be made to compensate for hanging weight of the pole. For this purpose the

over hanging portion of the pole may be supported on a movable trolley or similar device.

3.20.4 The pole is rigidly supported at the buttoned for a distance equal to the agreed depth of

planting.

3.20.5. Load shall be applied at a point 600mm from top of the pole and be steadily and gradually

increased to the designed value of transverse load at first crack. The deflection at this load shall be

measured.

A pre stressed concrete pole shall be deemed not to have passed the test if visible cracks

appear at a stage prior to the application of design transverse load for the first crack. The load shall

then be reduced to zero and increased gradually to a load equal to the first crack load plus 10% of

the minimum ultimate transverse load and held up for 2 minutes. This procedure shall be repeated

until load reaches the value of 80% of the minimum ultimate transverse load and there after

increased by 5% of the minimum ultimate transverse load until failure occurs. Each time load is

applied it is held for 2 minutes. The load applied to PSC poles at the point of failure and shall be

measured to the nearest 5Kgs.

The pole shall be deemed not to have passed the test if the observed ultimate traverse load

is less than the designed ultimate transverse load.

3.21. SAMPLING AND TESTING:

3.21.1. Lot-in a consignment of 500 poles or part thereof the same mounting height same

dimension and belonging to the same batch of manufacture shall be grouped together to constitute

a lot.

3.21.2 Sub-lot: If the number of poles in the lot exceeds 500 the lot shall be divided into

suitable number of sub-lots such that the number poles in sub-lot shall not exceed 500. The

acceptance or otherwise of a sub-lot shall be determined on the basis of performance of the

samples selected from it.

Size of lot Permissible defective samples for dimension

Permissible defective sample for strength

0-100 2 4

100-200 4 6

200-300 6 8

300-500 8 12

4.MANUFACTURING PROCESS OF TUBULAR PRESTRESSED CONCRETE POLE OF 11 METER LONG

The manufacture of Tubular PSC poles consists of the following operation:

1. Cleaning the moulds and oiling

2. Preparing the reinforcement cage

3. Placing of PVC inserts and through holes in the mould

4. Placing of the reinforcement cage in the mould.

5. Mixing of Concrete.

6. Placing the concrete in mould.

7. Placing other half of the mould and fixing.

8. Pre tensioning the wires.

9. Spinning the mould.

10. Curing with steam

11. Demoulding the pole.

12. Finished dimension of the pole.

4.1.Cleaning the Mould:

About the mould: Mould is made up of MS sheet. Mould of 11M length is made in two halves.

Each half is made of 4 pieces and joined to gather. Mould is stiffened with circular MS flats.

Enclosed drawing shows the detail.

One half of the mould will be placed on rollers and the other half on ground.

Cleaning: The mould halves are cleaned thoroughly with wire brush and oiled using REBOL oil.

Oil is applied to the moulds with a painting brush.

Dimension of the mould:

Length-11000 mm +or-15mm

OD (Big End)-392.5+4or-2mm

OD (Small End)-227.5+4mmor-2mm

The mould when placed on the rollers the bigger rest on rollers powered by motor and remaining

mould rests on support rollers. Spacing between drive roller and the support roller is 3000mm.

Number of rolling points is 5.

4.2 Preparing the Reinforcement Cage:

The reinforcement cage consists of the following:

a) 7 mm dia HT indented wire of 13.5 meter length-11nos.

b) 3 ply 3mm strands 5meter length –5nos

c) 6 mm dia 8.2meter length earthing rod-1no.

d) 2.7 dia coil 54meter long.

The coil is fabricated to helical shape in a machine. The pitch is 100mm.and 13.5meter long. and

the bigger end dia of 342.5mm the smaller end dia of177.7mm.The helical coil is placed on the

concrete mould having the shape of the pole placed on the ground. 3ply 3mm rods of 5meter are

inserted into the helical coil and binded to it by binding wire. 11nos HT indented wires of 7mm dia

are placed at equal spacing on the circumference of the coil the length of the wires being 13.5

meter the HT wires are tied to the coil by binding wire. These operations are made manually. End

plates are inserted to the cage.

4.3. Placing PVC inserts, Nuts and through holes in the mould:

The following are inserted into the mould at designated places:

PVC inserts-29nos.

M16 Nuts –2nos.

Through holes with nuts for fixing I-Bolts-5nos.

4.4 Placing of the cage in the mould:

The cage is lifted from the concrete mould by tower crane and placed on the MS mould for casting

of the pole. The end plates are fixed to the mould by bolts. Earthing rod is inserted into the cage

and placed at the designated place and welded to the MS 16 nuts placed in the mould

4. 5 Mixing of concrete

Cement of Birla 52 grade is used all required test are conducted at a reputed testing house and

results approved for the use of this cement. The tests are conducted for every batch of 200 bags.

Sand: Locally available sand is used. The sand is stored in shade. The tests conducted on the sand

in the factory laboratory are:

a) Bulking of sand

b) Specific gravity

c) Sieve analysis

d) Water content

The above tests are conducted for every load of cement. Water content of sand is estimated daily

and correction for water for mix is made.

Coarse Aggregate: Coarse aggregate of 12.5mm down size are procured locally and stored in

shade. The following test are conducted:

a) Sieve analysis

b) Surface dry

By trial method a mix of 1:1:2.5 with water cement ratio of 0.35 and a plastiziser Conplast SP430

300ml per bag of cement is used gives concrete of strength of M52.5

Concrete is mixed in a batch mixer .3 loads of concrete is required for casting the pole. Each load

consists of 85kg cement, 85kgs and 212.5kg coarse aggregate, 28.6litres of water, and 416Mlof

SP430 are mixed for 10mnutes in the mixer. The concrete is transported in trolley over the railing.

4.6 Placing the concrete in the mould:

Concrete transported is placed in the which is already with the mould.Concrete is placed manually

by the masons and compacted lightly with tamping rod. Care is taken so that quantity of concrete

mixed is uniformly placed throughout the mould starting from the bigger end. HT wires are button

headed at the bigger end securely. 9 cubes of 15 cms cubes are prepared for compression test.

4.7 Placing the other half of the mould:

The other half of the mould already oiled is lifted using a truss with chains

Using overhead crane. Care should be taken that the truss is properly fixed to the mould half by

shackles. This half mould is placed on the already concreted mould properly. For proper seating of

this mould is ensured through guide projections. After placing the mould the two halves are

thoroughly tightened using bolts and nuts

4.8 Pre tensioning the wires:

The HT indented 11nos wires are pre tensioned at the smaller end of the already casted pole having

fresh concrete. Pre tensioning is done using 2 hydraulic jacks. Diametrically opposite pairs of Ht

wire are pre tensioned at a time using two hydraulic jacks. The wires to be tensioned are buttoned

securely to the anchoring plate. The hydraulic jacks are inserted to the wires and buttoned headed

and load is applied to the wire manually. An extension of 115mm is obtained by applying pressure

through the jack. Normally 330 to 340kgper sq.cm pressure is recorded in the pressure gauge

attached to the jack. The extension required is obtained by Tension test results conducted on every

supply of wires. After tensioning of the wire the excess wire is cut. Care should be taken that no

movement of persons is allowed in front of the mould in the direction of tension. Some times if the

wires are not properly buttoned the wires may come shoot out of the mould with great force.

4.9 Spinning the mould:

After tensioning the wires all bolts are checked to its tightness. The mould at the bigger end is

connected to a motor for spinning the mould at required speed. Both the ends are covered with

covering plates and tightened with bolts.

Spinning is done as per the following speed and time.

TIME MOTOR SPEED RPM MOULD SPEED RPM

2 Minutes 550 72

3 Minutes 750 108

4 Minutes 950 136

9 Minutes 1100 156

The above speeds and time is arrived by trials.

4.10 Curing with steam:

After spinning cover plates at the bigger end is removed and the cubes already casted in moulds

are placed in the casted mould. Another cover plate which is having a hole for passing of the steam

is fixed. Steam is produced through a boiler. Steam of temperature 100 degree centigrade is passed

through already casted pole after 8 hours from mixing of concrete. Steam curing is done for 10

hours. The pole after demoulding is lifted and placed in curing water tanks for 14 days.

4.11 Demolding:

After cooling of the steam cover plates are removed. The cubes placed in mould are removed and

compressive strength found out. Tension is realsed by cutting the HT wires. The top half of the

mould is removed using truss and crane. I-Bolts are tightened to already existing through holes in

the casted pole. The casted pole is lifted by using the truss connected crane by fixing hooks to the

I-Bolt

4.12The Dimensions of the finished pole:

Bigger End Outer diameter: 392.5 mm Inner diameter: 292.5 mm

Smaller End: Outer diameter: 227.7 mm Inner diameter: 127.7mm

Thickness of the pole wall: 100 mm.

Length of the pole: 11000 mm.

4.13 Testing of Pole: Test bench is established in the factory on ground with rigid support at the

bigger end 1.5meter from the bigger end. Intermediate rollers are provided at 4 meter from as

required by BESCOM. Load is applied as pull from a dynamometer at the smaller end and load at

first crack is noted. This load should not be less than 500Kg. Test is also carried out to destruction

of pole and the load at destruction is noted.

5. TIME STUDY :I was asked by the company to monitor the manufacture time of the pole and

to make work study report. A sample work study format is enclosed. Work study was done and

after 20 days of monitoring and making changes in work allotment to employees time for casting

pole was reduced by 70 minutes.

7.CONCLUSION:

1.The pre stressed have a longer life compared to wooden or steel pole without maintenance cost for corrosion protection.

2.Because of its circular tapering section it has more stability and has ability to resist shear force and bending moment.

3.Since manufacturing process involve spinning process which is one of the best method of casting freshly cast concrete,has the centrifugal forces applied to concrete,secure a dense,excellent quality concrete at relatively less manufacturing cost.

4.Because it is pre fabricated the production of pole is consistant.

5.The pre stressed hallow or tubular pole have proved to be more economical,easily transported and erected due to light weight.

8. TIME STUDY FOR POLE CASTING.

Sl.No Description Time in minutes

1 Inserts Releasing 20

2 H.T Wire cutting 30

3 Bolts and nuts removing 30

4 Demoulding 20

5 Pole releasing 15

6 Pole shifting 15

7 Cleaning of mould 40

8 Cage fixing & end plates 15

9 Inserts fixing for first half 15

10 Mixing first load of concrete 15

11 Pouring of 1st load 15

12 Mixing and pouring of 2nd load 15

13 Mixing and pouring of 3rd load 15

14 Mould assembling 30

15 Pre tension 30

16 Spinning 20

TOTAL 245