post tensioning system

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k) Protection to reinforcement in case of concrete exposed to harmful surroundings may also be given by providing a dense impermeable concrete with approved protective coatings, as specified by the Engineer.

l) The correct cover shall be maintained by cement mortar cover blocks. Reinforcement for footings, beams and slabs on sub-grade shall be supported on precast concrete blocks as approved by engineer. The use of pebbles or stones shall not be permitted.

Inspection Erected and secured reinforcement shall be inspected, jointly measured and recorded and approved by Engineer prior to placement of concrete.

1.4 POST TENSIONING SYSTEM Design, material, supply and execution of post tensioning works to all floors including

decoiling the strands, cutting to the required lengths, supplying and laying of HT strands, sheathing (GI corrugated ducts 80mmx20mm, 0.30mm thick jointing with couplers and inserting the strands, profiling, fixing live end anchorages including the supply of stressing anchorages suitable for 5-5 and 5-4 Tendons, grout vents, making dead end anchorages including flowering the strands, fixing Tendon support bars, supervising the fixing of anti brusting reinforcement, stressing the cables, end trimming grouting the cables with cement and admixtures with required plant and machineries, tools and tackles, consumables etc. including cost and conveyance of all materials, labour charges, approved drawing and technical specification as directed by the Engineer-in-Charge.

General The Post Tensioning bonded Beam slab system shall consist of High Tensile strands of

12.70 mm (0.5dia) /15.20 mm dia ( 0.6 dia) and contained in a flat slab GI duct of 80 mm x 20 mm. Each strand in anchored by means of wedge and individually stressed by means of a mono strand Jack. The prestressing force is transferred to the concrete by a flat anchorage.

Prestressing systems The pre-stressing system is incorporating strands with 12.70 mm dia strand /15.20 mm dia

strand. Materials

Strands 0.5 0.6 Nominal Diameter 12.7mm 15.2mm

Nominal Area 98.7mm 139mm2

Nominal weight 0.775 kg/m 1.101 kg/m

Tensile strength 1860 N/mm2 1860 N/mm2

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Modulus of elasticity 195 N/mm2 195 N/mm2

Min breaking load of strand 184kN 184kN Strand quality in accordance with IS 14268 IS 14268

Sheathings The sheathings for bonded tendons shall be spirally wound galvanized iron tubing made

from galvanized iron strips of 0.3 mm thickness. The sheathings shall be mortar tight to prevent entrance of cement grout during concreting

and shall be corrugated for better bonding. The sheathings shall be sufficiently strong to retain shapes and to resist damages during

construction. The round sheathings with various outer diameters from 68mm to 135 mm have been

widely used in Multiplane anchorage systems. Ducts The sheathing consists of corrugated spiral ducts made from galvanized iron strips of 0.3

mm thick. Anchorages The type of anchorages commonly used is Flat Anchorage (FA), Multiplane Anchorages

(MA), Bond Head (Dead End) Anchorages. The purpose of the anchorages are when the strands are stressed, the tendon force would be transferred to the concrete. Bursting reinforcement is provided behind the anchorage to distribute the stressing force.

Design data for friction / elongation calculation Friction coefficient u : 0.2 } or as per the consultants Recommendation

Wobble factor k : 0.0017/m } design parameters

Draw in of wedge : 6mm (approximately)

Stressing anchorage : Type FA, MA

Loss in jack : Varies from 0 to 2.0% for various type of

jacks Handling and storage of materials The pre-stressing strands shall be free of grease and corrosion enhancing proper ties. No flame cutting of strands is allowed

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Care should be taken during handling of construction work in order to avoid mechanical

damage to the strands. Strands should be raised above ground level to prevent ingress of soil. Suitable ropes or slings shall be used for loading and unloading in order to avoid

mechanical damage to the strand coil. The component must be handled and stored such that any contamination, mechanical

damage or corrosion can be avoided. General Working Procedures Post Tensioning tendons shall be installed in accordance with the Approved Drawings

issued for Construction. For Post Tensioning slabs construction Install bottom slab reinforcement when the slab formwork is ready. Provide sufficient cover to the bottom slab reinforcement Method Statement of Post-Tensioning System Install top slab reinforcement for Post Tensioning beams construction Install bottom and side reinforcements and links. No capping links shall be installed at

this stage Install tendons in accordance with the shop drawings. Install top reinforcements and capping links of the beams Guidelines for Tendons Installation Tendon alignment and height shall take precedence over reinforcement whenever there

is a clashing point. All dimensions measured shall be based on the formwork level. Therefore an accurate

formwork level is necessary. The tolerances of formwork shall be + 5mm or in accordance to the specifications. The Multiplane Anchor is fixed to the end formwork by support bars to avoid any

displacement during concreting. The Multiplane Anchor must be orientated perpendicularly to the cable axis and with the

grout connection at the top of the duct. Tolerances for vertical tendon profiles are +10mm for all high and low points.

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Tolerances for horizontal profiles are +150mm (to avoid small M&E openings or other

obstructions). Specialist designer shall be consulted for tolerances bigger than +150mm. Handle ducts with care to avoid damage. Support bars and bar-chairs are placed at intervals of each 1m (approx) and secured

with binding wire to avoid any movement during concreting. Duct joints are sealed with tape. Care should be taken during concreting to avoid grout hoses from being embedded in

concrete or removed completely. Avoid stepping on ducts placed. Care should be taken to avoid damaging ducts with tie bars of the formwork. Tendon support and bar chairs are placed at 1m interval and secured with binding

wire to avoid movement during concreting. Check visually on the ducts straightness and do necessary adjustment before concreting Grout hoses must be protected from being embedded or removed during concreting Any defect found in the bulb of strands such as breakage of ply should be replaced with

new bulb. Compressive strength required for commencing stressing operation shall be 75% of the

concrete grade used or minimum of 26N/mm2 Preparation for stressing Removal of formwork and polyfoam / plastic block out from the anchorage

blackout. Placing of wedge plate and wedges. It is important that this operation be carried out

after concreting so that the anchorage is not fouled by grout or dirt. Ensure that the protruding strand length is sufficient for stressing. The theoretical elongation calculations must be approved by the consultant before

stressing For Multistrand Jacks (Multiplane Anchor) At the beginning of stressing the strands are locked in the jack pulling head. The pressure of the manometer and the measured elongation are recorded in the

stressing report. When the jack has reached the end of its stroke or the desired force has been obtained,

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the pressure in the jack is released and the strands become locked uniformly by the wedges in the wedge plate.

The jack piston returns. Stressing is continued in as many stages as are necessary to obtain the required force. For Monostrand Jack (Flat Anchor) Initial stressing of 25% of the total designed force can commence anytime after the

concrete has minimum cube strength of 8N/mm2. The purpose of initial stressing is to take the slack of the strands in the tendon.

A spray mark is made on the strands. Proceed with the full 100% stressing of the total designed force after the concrete has

attained its minimum strength as per the specifications. Measure the difference in length from the spray mark to the wedge plate. This will

reflect the elongation per strand from 25% to 100%. (Assume this to be X mm in length.)

Add the wedge draw in which is approximately 6mm to the elongation. By extrapolation the full measurement can be calculated and compared against

theoretical elongation. Therefore the full elongation for one-end stressing will be = (X + 6mm) x 100 ------- % = (X + 6mm) x 1.3333 75 Similarly for tendons with two ends stressing, the tendons may be stressed from one

end followed by another. Sum of elongations from both ends is then compared with total theoretical extension.

Assuming the far end elongation is Y. The total elongation will be: {(X + 6mm) + (Y + 6mm)} x 100 ------ % 75 Sample of Stressing Reports are as shown in Appendix A.4 After approval by consultants / main contractor the protruding strands are to be cut off to

a minimum of 10mm from the wedge plate. All stressing results shall be tabulated on a stressing record and submitted for approval

by the engineer. The pressure gauge and jack nos shall also be indicated.

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If the average stressing result of the whole pour is within +8% it shall be deemed as satisfactory.

In accordance to the Federation Institute of Prestressing (FIP) code, the average shall be

within +8%.If any individual tendon of a pour falls outside this, then the average extension over the whole respective pour should be checked and this falls within the tolerance of +8%, then the stressing operation is considered satisfactory.

Stripping of formwork can be carried out after full stressing of beam / slab is completed. Grouting Grouting shall not commence unless the consultant has approved the stressing result Preparation of Grouting Cut the Protruding strands (stressing length) to a minimum of 10mm from the wedge

plate. The anchorage blackouts shall be filled with the approved cementations material. Proposed grout mix Cement in standard 50kg package (Ordinary Portland cement)

Water = 0.45 x 50kg = 22.5 kg = 22.5 liters Admixture = 0.4% weight of cement (50 kg) = 200gm (Conplast Fosrac)

Mixing sequence = water - additive cement

Min mixing time = 3-4 min Tests for grouting Measurement for compressive strength of grout cubes During trial mix period, compressive strength test shall be carried out. 6 samples per grouting session are required. After 18 to 24 hours, remove cubes from mould and store in water storage tank. Compressive strength shall be measured for 7 & 28 days. According to specification ,compressive strength of cube shall be:

7 days : minimum of 17 N/mm2 28 days : minimum of 30 N/mm

(BIDDER)


Grouting of tendons After the trial mix is done and a suitable mix is determined, than the grouting is ready to

proceed. Prior to grouting, all anchorage block outs are to be patched up by cement / mortar or

equivalent approved mortar based material. After this is completed and the mix is ready, start injecting grout from the inlet hose of

the tendon. When grout outflow appears at the intermediate vents, close vents in direction of grout

flow. Grout must flow out from outlet until visible residual water and entrapped air has been

removed. Lock the outlet hose. Continue pumping until the desired pressure of 3-5 bars is achieved. Close the inlet hose

and proceed to the next tendon. Precautions to be taken during grouting. Pressure should be duly controlled so as not to cause segregation of grout. Excessive mixing (especially at high temperatures) can stiffen the grout already in the

mixing drum. In case of interruption (more than 45 minutes) the grout shall be flushed out of the

tendon using water and compressed air. Scope of work: The scope of work shall include: i) Submission of detailed design and corresponding calculations vetted by IIT(Indian

Institute of Technology) for the Beam slab by post tensioning system in accordance with the design parameters specified by the Consultant, the codal requirements of BIS (Bureau of Indian Standards) latest versions and National Building Code to the Engineer in Charge/Consultant.

ii) Prepare detailed shop drawings for the post tensioning work to be carried out by

showing clearly all the dimensions, spacing and all other required constructions details and obtaining approvals of same from Consultants well in advance to have sufficient time for procurement and delivery of material and equipment and to carryout the work in accordance with the requirement of overall construction schedule.

iii) To assist and guide the civil contractor for any works directly or indirectly related to or

consequential to the post tensioning of the Beam slabs. iv) Prepare and submit three sets of As Built drawings for each post tensioned slab showing

clearly the profile and location of each tendon

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Prime Responsibilities of Post-Tensioning Contractor The Post Tensioning contractor shall ensure the following during each stage of work and

shall remain entirely responsible for the same. 1) Design calculations (vetted by IIT ((Indian Institute of Technology)) shall be

submitted and got approved by Consultants/ Engineer-in-charge prior to commencement of work at site

2) That the tendons are not disturbed while concreting. In case they are disturbed their

position shall be reinstated immediately contractor shall post their supervisors and workers for this purpose at site to remain in full attendance during concreting operation. Contractor alone shall remain fully responsible for placing the tendons and ducts in accurate profile and maintain the same during and after concreting of slabs

3) Contractor shall independently ascertain that concrete has achieved necessary strength

before tendons are stressed and anchorages are jacked against the slabs. Specifications All the work shall be of the highest possible workmanship and best available material as

approved by Engineer in charge. The materials used for the work shall be strictly in accordance with the specification as above.

Quality Assurance Procedure of PT Structure Materials Concrete Concrete mix and design strength required for prestressed concrete work shall be as

provided in the drawings and in the specifications, Concrete work shall conform to the Concrete work specification.

Trial batch shall be made and tested at 1, 3 and 28 days to prove the specified design

mix before construction commences. The contractor shall assess the age at which the concrete mix will reach the required transfer strength for stressing operation.

Prestressing Steel Steel strands used in post-tensioning tendons shall conform to BS 5896:1980/Class II

14268-1995 for Uncoated Seven-Wire stress-Relieved strand for prestressed Concrete or ASTM A416. Unless otherwise stated the ultimate tensile strength shall be 1860 N/mm2. Oil tempered strands shall not be used.

High strength alloying steel bars shall be cold stretched Proof stressed during

manufacture, to the minimum yield strength. After stretching, all bars shall be subjected to a stress-relieving heat treatment to produce the required physical properties.

Bonded Prestressing Systems

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Anchorages Anchorages for bonded tendons shall develop of the minimum specified ultimate

strength of the prestressing steel, tested in an unbounded state without exceeding the anticipated set, the anchorage being so arranged that the prestressing force of the tendon may be verified prior to the removal of the stressing equipment, if so desired. All Post-Tensioning anchorages shall have gone through stringent testing in the laboratory.

Sheathing Sheathing material for bonded tendons shall be spirally wound-galvanised steel tubing

unless otherwise specified and shall be strong enough to retain shape and to resist unrepairable damage during construction, Round ducts or oval ducts/flat shall be used for beams unless otherwise approved by the Engineer.

Such sheathing material shall prevent the entrance of cement paste from the concrete

and sheathing shall be corrugated for better bonding. Grout The grout for bonded post-tensioned concrete members shall be a neat cement grout

made with ordinary Portland cement, water and admixture approved by the Engineer in charge.

The grout shall have a minimum, compressive strength measured on 100mm cubes as

17N/mm2 at 7 days and 30 N/mm2 at 28 days. Two sets of three cubes shall be taken on each day of grouting, one set shall be tested at

7 days and one set shall be tested at 28 days. The grout shall be sufficiently fluid and of a uniformly colloidal consistency to enable

the cable ducts to be grouted using maximum pressure of 0.5N/mm 2. Pressure should not be lower than 0.2 N/mm 2 . The grout shall have a maximum cement ratio of 0.45, except where otherwise agreed in writing by the Engineer in charge.

Other additives, which reduce shrinkage and/or increase workability, may be used

subject to the written approval of Engineer in charge. All ducts shall be clean and free of deleterious materials that would impair the bonding

of the grout or interfere with grouting procedures. Each duct shall be thoroughly flushed and blown out with water and compressed air prior to grouting.

General Standards and Codes of Practice Unless otherwise stated, Indian codes and standards are used herein to lay down the

minimum standards required for prestressed concrete work, in particular, the specifications, standards, tests and recommended methods prescribed by IS code of practice shall determine the quality of material and the method of work. In cases where

(BIDDER)


above standard are not available, FIP (Federation Institute of Prestresssing) guidelines shall be used as reference.

System of Prestressing The system of prestressing used, shall be the Post-Tensioning systems as approved by

the Engineer. The system shall be used strictly in accordance with the written recommendations of the manufacturer.

The effective prestressing force has been calculated using the parameters shown on the

drawings and based on the Post-Tensioning systems, The Bursting and spilling reinforcement has been designed and detailed considering the

dimensions of the Post-Tensioning systems. Storage of Prestressing Components Prestressing components shall be stored in clean conditions, and shall be cleaned and

free from pitting and loose rust at the time of fixing in position and subsequent concreting.

Materials Tests Required Submittals for Prestressing Steel The contractor shall submit to the Engineer in charge, Mills certificated from the

manufacturer of prestressing steel showing that prestressing steel meet IS Specifications and are suitable for the purpose intended.

Laboratory Tests. A 1.0m long of strand shall be tested by testing Authority and test certificate shall be

submitted to the Engineer in charge. The Contractor shall ensure that all prestressing steel shipped to the site are assigned

individual lot numbers and tagged for identification. Prestressing Operation General Prestressing shall be carried out by approved method and equipment related to generally

accepted system of prestressing. Variations of such generally accepted methods and equipment shall be permitted provided the Engineer is satisfied that equal results can be obtained.

Prestressed concrete work shall be carried out under the immediate control and close

supervision of a person experienced in this type or work. Prestressing Strands

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The length of tendons shall be determined accurately to facilitate installation without changing of forms. Where the lengths of tendons cannot be determined from the Drawings, site measurements shall be taken.

Sheaths All sheaths shall be maintained in correct positions during the placing of the concrete.

The sheaths shall be rigidly supported at points no more than 1.50 m apart. Where sheaths are used, the number of joints shall be kept to a practicable minimum.

Each joint shall be adequate sealed against the ingress of any material and shall be mortar tight.

Sheaths shall be kept free on any matter detrimental to the bond between the sheath and

grout and, except for material sealing a sheath joint, between the sheath and the concrete.

The number and position of grout vents for entry and outlet points, shall be adequate

provided. Standard PVC 3/4" diameter hose shall be used to act as grout hose. Jacks for Prestressing All jacks used for prestressing shall be of the type applicable to the system adopted. All jacks and gauges to be used for the project shall be calibrated by an approved testing

authority. The validity of each calibration record is set at 1 Year. Jacking shall be performed from either one end or both ends of post-tensioned

prestressing strands, as stated on the shop drawings. Post-Tensioning Procedure The tendons shall be stressed when the concrete reached a minimum strength as

specified on the Drawings. Unless otherwise permitted by these specifications, concrete shall not be stressed until it

has reached at least the age at which test cubes taken there from attain the specifies transfer strength. The test cubes shall be made and tested but shall be cured in similar conditions to the concrete to which such relate. The Contractor shall cast sufficient cubes to demonstrate that the required strength of the concrete at transfer strength has been reached.

The force in the tendons shall be obtained form readings on a pressure gauge, and the

extension of the tendons measures. The two readings shall conform to the limits set by the engineer but in any case the force in the tendon as computed form the extension measurement shall be within + 8percent of the force (as mean value of all tendons in that particular pour). Please refer to the method of statement Post-Tensioning systems manual for the interpretation of stressing results.

Over length of strands at anchorages shall be cut off and patched with approved mortar

after completion and approval of stressing operation by Engineer in charge.

(BIDDER)


Safety precautions shall be taken to prevent workers from standing behind the jacks,

when strands are being tensioned. The Contractor shall keep full records of all tensioning operations, copies of these

records shall be supplied to the Engineer in charge after each tensioning operation. Full records are to include the following data:-

i. Identification number of gauges and jacks. ii. Identification particulars of tendons. iii. Identification of the structural member where the tendon is used. iv. Initial force(or pressure) whereon tendons are marked for measurement of

elongations. v. Final force (or pressure) and elongations obtained on completion of tensioning. vi. Hydraulic pressures.

vii. Elongation obtained at suitable intervals during tensioning together with

corresponding force(or pressure) if and when required by the Engineer. Grouting of Ducts Ducts shall be grouted as soon as practicable after the tendons have been stressed and

the Engineer in charge permission to commence has been obtained. Grout shall be injected in one continuous operation, and allowed to flow from the vents until the consistency is equivalent to that being injected.

The ducts shall be completely filled with grout. Vents shall be sealed consecutively in the direction of flow. Inspection The Engineer in charge shall be notified before any concrete in slabs or beams is cast, so

that inspection of the tendons and reinforcement can be made. Shop Drawings The Contractor shall submit for the Engineer in charge is approval, before the

commencement of construction, shop drawing showing the location, number of strands in tendons.

Safety

i. Hand Tools must be double insulated. ii. All the electrical items shall be protected with 30MA ELCB.

(BIDDER)


iii. All the cutting machines shall have protection guard for the blade. iv. All the PPE (personal protective equipment) shall be used in the site. v. All the works like stressing, cutting etc shall be carried out from the proper

scaffolding only. vi. Do not stand at the jack and on the direct line of the tendon being stressed. vii. In addition secure the complete area by adequate restriction and with a DANGER

SIGN. Measurements The length of strands shall be measured correct to a cm from Anchorage to Anchorage

including Stress-ing Length + 2% profile length . Stressing length for Flat Anchorage is 500mm and for Multi Anchorage it is 1000mm. The quantity shall be calculated on their weights on the basis of standard tables as per IS 14268 correct to the nearest quintal unless otherwise specified.

Rate The rate shall include the cost of all materials and equipments for the post tensioning work

including the rate of tendons,anchorages,grout etc including T & P, scaffolding and labour involved in all the operations described above including fixing/installation, lead & lift and all taxes like, Sales Tax/VAT, Excise duty, Octroi etc. as applicable.

1.5 MASONRY WORKS

Applicable codes and specifications

The following codes, standards and specifications are made a part of this specification. All standards, tentative specifications, codes of practices referred to herein shall be the latest edition including all applicable official amendments and revisions.

IS:1077 - Common burnt clay building bricks

IS:3102 - Classification of burnt clay bricks

IS:2180 - Burnt clay building bricks, heavy duty

IS:3495 - Method of sampling and testing clay building bricks

IS:2691 - Burnt clay facing bricks

IS:2221 - Code of practice for brick work

IS:2185 - Concrete masonry units Hollow & Solid Concrete Block

IS:5498 - Lime-cement-cinder hollow concrete blocks

IS:3115 - Lime-cement cinder solid blocks

IS:1597 - Code of practice for construction of stone masonry (Part I)

post tensioning system

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