PRACTICE CODE for Execution of Concrete, Reinforced Concrete and Prestressed Concrete Works

(Part II- Prestressed Concrete)

INDICATIVE NE 012-99

CONTENTS

Chapter 1. General Provisions

Field of application

General requirements for execution of concrete works

Chapter 2. Formworks, models, formwork supports

Chapter 3. Prestressed reinforcements

General provisions

Manipulation, haulage and storage

Preparation for production of prestressed reinforcements.

Manufacturing and positioning of prestressed/ pre-elongated reinforcements

Manufacturing of the post-elongated reinforcements

Execution of canals for post-elongated reinforcements

Mounting the post-elongated reinforcements

Chapter 4. Locks/ Locking systems, blockage systems

Chapter 5. Performance requirements and criteria concerning concrete for prestressed concrete elements/ structures

Chapter 6. Execution of joints for elements or constructions built from arch bricks an precast panels, assembled through precompression

Chapter 7. PRETENSIONED REINFORCEMENTS

Pre-elongated reinforcements

Post-elongated reinforcements

Chapter 8. EXECUTION OF PROTECTION SYSTEMS AGAINST CORROSION AND ADHERENCE OF POST-STRESSED REINFORCEMENTS

General Provisions

Injection/ Jetting

Injection/ Jetting under low temperature conditions
Protection of exterior pretensioned reinforcements

Chapter 9. QUALITY CONTROL AND ACCEPTANCE OF PRESTRESSED CONCRETE WORKS

Chapter 10. MEASURES CONCERNING WORK SAFETY TECHNIQUE AND FIRE PROTECTION

APPENDIXES

1. Reference documentation

2. Specific notions for precompressed concrete

3. Details and technical requirements to be indicated in the execution design or in the technical specifications

4. Main characteristics of INCERC procedures of precompression with post-elongated reinforcement

5. Systems produced by INCERC for execution and mounting of reinforcements and for protection by jetting.

6. Construction of canals with bundles, as per appendix 4

7. Execution and acceptance of metallic locks of types ring-cone and mandrel

8. Individual blockage with sleeve and wedge grips/ dies for braids (manson si bacuri pentru toron) 7ф4 mm for pre-elongated reinforcements

9. Pretensioning systems for pre-elongated reinforcements, manufactured by INCERC

10. Pretensioning systems for post-elongated reinforcements, manufactured by INCERC

11. Determination of friction coefficients (k, μ), the elasticity module (E) and elongations (Δl)

12. Methods of drawing up the pretensioning sheet/ indications/design for post-elongated reinforcements

13.Determination of the characteristics of the jetting mixture/ jetcrete.

14. Methods of drawing up the jetting/ injecting sheet/ instructions

PRACTICE CODE FOR EXECUTION OF CONCRETE, REINFORCED CONCRETE AND PRESTRESSED CONCRETE WORKS

Part B: Prestressed concrete

1. GENERAL PROVISIONS

Field of application

Provisions of part B of Practice Code for execution of concrete, reinforced concrete and prestressed concrete works refers to execution and acceptance of constructions and construction elements made of concrete, prestressed with pretensioned steel reinforcements, using INCERC procedures.

Practice code provisions shall be adapted and completed via specific regulations (or, if such regulations are not available, based on technical specifications or task books drawn up by the designers) in the following cases:

- Constructions with pretensioned reinforcements, whose adherence with the concrete is not ensured for their entire length

- Constructions subjected to pressure exerted by liquids or gases

- Constructions subjected to systematic action of temperatures outside of the interval 35+50C.

- Constructions in the neighbourhood of RADIOACTIVE sources, for example nuclear power plants

- Constructive located in aggressive natural and industrial environments whose adequate protection systems have not yet been established through regulations

-Constructions with outstanding resistance structures or with special exploitation requirements, for which special regulations are drawn up.

- Constructions executed after designs executed abroad, which are based either on international and European standards or on national norms

Observance of the provisions hereunder is mandatory for investors, designers and commissioners of prestressed concrete constructions or elements that employ INCERC procedures.

1.4. Execution and acceptance of prestressed concrete constructions and construction elements which are manufactured with other materials, or prestressing procedures, shall observe the provisions of the practice code hereunder, the provisions contained in the technical agreements enforcing the use of such materials, as well as provisions contained in the technical specifications of manufacturers/ creators of these materials and procedures

The technical agreements for procedures and materials (produced) for precompression, are drawn up in compliance with the Regulations concerning the technical agreement for new construction products, procedures and equipment (Govt. Decision No 766/1997), and in compliance with the following Guides:

- Guide concerning agreement methods for reinforcements for precompression used in civil, industrial and special constructions GAT 253 (MLPAT)

- Guide concerning agreement methodology for locking and blocking systems (anchorage) for precompression, used in civil, industrial and special constructions- GAT 254 (MLPAT).

Reference documents

Reference documents are presented in appendix a.

Terms, notation

Specific terminology is defined in appendix 2.

General requirements for execution of prestressed concrete works

Prestressed concrete works shall be executed based on a design, drawn up by a specialized design unit and audited by specialized and certified design auditors.

INCERC precompression products, pretensioning equipment and systems are indicated in appendixes 4, 5, 6, 7, 8, 9, 10 and 13.

The products indicated in the INCERC precompression procedures shall be certified for quality compliance via a third party, in compliance with provisions of the Regulations concerning quality compliance certification for construction products (Govt. Decision no 766/1997).

Precompression works shall be performed by companies able to ensure the required level of quality for prestressed concrete constructions, through a certified quality system, with certified supervisors of works.

Prestressing works (pretensioning, jetting) shall only be performed by teams that comprise at least one member in possession of a valid specialized professional certification, issued by INCERC.

The constructor is also obliged to make sure that the design contains at least the data indicated in appendix 3.

Investors are obliged to verify that works are correctly executed, through specialized supervisors or specialized consulting companies.

The owners of prestressed concrete constructions have the following obligations:

- to timely perform all maintenance and repair works

- to ensure monitoring of construction behaviour over time and if necessary to request extended inspection concerning durability status, technical examination, consolidation designs, from research institutes or specialized, certified specialists.

- to perform consolidation or repair works necessary, based on designs drawn up and verified in compliance with legal regulations.

Verified from research institutes or specialized certified specialists

2. FORMWORKS, FRAMES, SUPPORTS FOR FORMWORKS

Formworks, frames together with their supports, used in prestressed concrete works, shall only be executed based on construction drawings drawn up by design units in compliance with provisions of STAS 7721-90 as well as those in Part A of the practice code hereunder- Concrete and Reinforced Concrete.

In the case of formworks for prestressed concrete structural elements, deviations shall be indicated in the design or they shall be established by the constructor, based on the precision class indicated in the design. Usually, in the case of wooden forms, the precision class shall not be higher hat CP 7; generally the resulted elements shall be placed in the immediately inferior class.

Apart from requirements in Part A of the practice code hereunder, the forms, frames and supports must also meet the following conditions, specific for prestressed concrete works:

- to enable mounting and dismantling of prestressed reinforcement deflection systems;

- to enable safe anchorage in compliance with the design, of the pieces embedded in end areas (distribution plates, joining funnels, covers/ casings), and to enable the temporary assembly pieces, which cross the concrete layer, to be eliminated/extracted/ taken out easily.

- to enable appropriate compaction in the anchorage areas of the pretensioned reinforcements.

- to enable elastic shortening at precompression and working of the net weight.

- to ensure the appropriate traffic and working locations/ positions for the personnel performing concrete casting and compaction; traffic over pretensioned reinforcement shall be avoided.

- formwork supports shall enable access and arrangement of the work platforms so that concrete pretensioning and jetting can be performed, provided they cannot be performed from already finished parts of the construction.

In the case of formworks for prestressed elements or constructions used for waterproofing or sealing against gases, formwork connection pieces shall not be introduced into the concrete layer. If this is not possible other appropriate solutions must be avoided, which have been properly verified through tests, concerning the possibility of waterproofing of the areas crossed by the respective connection pieces.

Chemical waterproofing materials shall only be used upon technical approval.

Working platforms of the gliding forms/ formworks shall allow storage and mounting of cases for bundles/ bundles, as well as to ensure control of their continuity.

3. PRETENSIONED REINFORCEMENTS

General provisions

Steel products to be used as pretensioned reinforcements shall observe requirements and performance criteria in technical specifications TS 009-1996 (position 6, appendix 1).

The designer can indicate in the technical specifications that additional verifications be performed, apart from TS 009-1996, specifying the technical regulations based on which the respective verifications shall be performed.

Replacement of a steel type adopted in the design with another steel type is only allowed based on design or expert approval, even if the replacement steel type exhibits superior features.

Imported pretensioned reinforcements shall be used based on technical agreement, in compliance with the Guide concerning approval methods for precompression reinforcements used in civil, industrial and special constructions- GAT 253 (MLPAT).

In the absence of data concerning transmission length (l) and anchorage length (l), these length values shall be determined by an authorized laboratory, in compliance with Romanian norms and, in special cases, taking into account the national norms in the country the steel has been imported from.

Steel products equipped with permanent anti-corrosion protection layers, applied in the factory, shall comply with provisions in the technical specifications of the designs, both concerning steel and protection layer features, as well as concerning acceptance requirements for the constructors. If these steels are used without additional protection, before issuance of technical agreements, reports shall be analysed, concerning tests of effectiveness of protection layers against corrosion various areas of the construction, but especially in the anchorage area, on the entire duration of the construction.

Apart from compliance with technical specification TS 009-1996, steel products for pretensioned reinforcements to be subjected to mechanical processing needed for the anchoring system (cupping/ drawing, threading/ screw-cutting/ thread-cutting/tapping etc) shall comply with specific requirements for these processing methods, to be established by the initiator of the procedure.

Manipulation, transport and storage

The following provisions shall be observed during transport and storage of steel products to be used as pretensioned reinforcements:

a) Haulage shall be performed in closed wagons or in trucks equipped with tarpaulins/ tarpaulin tops; these vehicles shall be first cleaned of any waste that may cause steel corrosion or contamination phenomena- especially oil products (Vaseline, various oils)

b) Storage shall be organized on lots and diameters, in closed and appropriately ventilated spaces, on supports that prevent contact with the floor or with corrosive materials. Placement methods shall enable access to each batch for periodical control.

c) In the case of non-aggressive storage spaces or spaces with very low aggressiveness, with humidity values below 60%, no additional protection measures are required.

d) In case the storage facility is placed in environments with low or average/ moderate aggressiveness, with humidity values below 60%, the maximum storage duration is indicated in the table below.

* definition as per instructions C170-87

The indicated intervals can only be exceeded is long-term temporary protection layers/ protections are used, established by a specialized institute; the same rule is applied to steels with permanent protections.

e) In the case of bundles and drums equipped with special protection packages, applied in the factory, special attention must be given to maintain integrity of the protection package during haulage, manipulation and storage; if the protection package has been deteriorated, then provisions for unprotected reinforcements shall be observed. The effectiveness of the package for the respective storage conditions shall be verified periodically on test batches.

f) The necessary measures shall be taken during haulage, manipulation and storage of steels, in order to prevent the following:

- scratching, hitting of bending

- contamination with soil, fat materials, dust etc

- contact with the incandescent material generated by activities of welding, cutting or flame-heating with the acetylene welding equipment.

- covering the steels with materials that may maintain humidity, for a long time.
g) Manipulation and haulage of reinforcements by pulling/ dragging on the ground is forbidden.

h) The bars shall be delivered in a rectilinear shape; they shall be manipulated, hauled and stored so that their shape is preserved. Possible works at the ends of the bars shall be protected by sleeves against corrosion or mechanical degradations.

Preparations for manufacturing pretensioned reinforcements

The following operations are included in the preparation works:

a) Verification of existence of the quality certificate for the steel lot the reinforcement will be executed from; if there are any doubts regarding observance of haulage and storage conditions- signalled by the occurrence of rust, contamination, deformation etc- quality verification tests shall be performed, in compliance with provisions of the product standards, by the production unit or by an authorized laboratory, in order to confirm that reinforcement physical and mechanical features were not negatively influenced. In all cases of uncertainty over the corrosion status and it consequences, approval from a specialized institute must be requested.

b) The surface of the steel shall be cleaned of impurities, of the non-adherent superficial rust layer and it shall be degreased (if necessary), in order to ensure proper anchorage into the blocking systems, into the concrete or into the injection mortar.

c) The reinforcements that are to be simultaneously tensioned must originate from the same lot, if possible.

d) Reinforcement sections subjected to local bending, which remain deformed, shall no longer be used; straightening operations are forbidden.

Pretensioned reinforcement sections (tendons, braids) that have been affected by the electrical arc of the welding equipment shall be removed.

Bars of superior steel subjected to slight deformation (<5 cm/m) during haulage or storage shall be straightened mechanically at the temperature of the environment, but at least +10C.

e) Re-reeling of the tendons and braids, for various technological purposes, at diameters smaller than the initial delivery diameters.

In the case when the control of the pretensioning effort/ strain is also performed by elongation of the reinforcement, the value of the reinforcement elasticity module must be known. in the case when the control of the pretensioned effort

For individually pretensioned reinforcements, the elasticity module shall be determined by a specialized laboratory, in compliance with provisions of STAS 6605-78.

In the case of post-elongated bundles/ bundles indicated/ specified in appendix 4, a global elasticity module shall be considered, equal to 1.92 x 10 N/mm2, with variation limits 2%. Or other types of bundles/ bundles, this elasticity module shall be indicated by the designer of the respective bundle/ bundle type, or it shall be determined by authorized testing laboratories. For important constructions, or in case conditions allow it (bundles with rectilinear routes or with constant curves), it is recommended that the actual value of the elasticity module be determined on the construction site, once tension loss caused by friction on the route have been determined.

The re-reeling and discharge devices appropriate for each reinforcement type shall be checked in order to make sure that the length and inclination of cutting sections (more exigent, for example, in the case of reinforcements with bulbs at their extremities) are correct

Production and positioning of pre-elongated reinforcements

The methods of production and positioning of pre-elongated reinforcements as well as of the other reinforcements and embedded pieces (as the case may be), shall normally constitutes the object of the technological design of the prestressed concrete element.

Reinforcements shall be cut in length so that there are no deformations on the section that might prevent introduction of the reinforcement into the distancing screens, in the inventory blocking systems of the pretensioning installations, or other technological operations. During discharge, the brains where one of the component tendons has been entangled should be eliminated- provided such areas can be identified.

Special attention must be granted in order to avoid contamination of the reinforcements by contact with greased areas of the frame walls or the walls of the casting platforms.

Position deviation of the pretensioned reinforcements into the section of the element shall not exceed 3 mm from the design reference position, if not otherwise specified. No negative tolerances are allowed in reference to the thickness of the concrete cover layer of pre-elongated reinforcements.

In order to place and to preserve the position of pre-elongated reinforcements as indicated in the design, distancing metallic screens shall be used. In stand technology, some of these screens are fixed and others are movable. The diameter of screen holes shall exceed the diameter of the pre-elongated reinforcements by 1-2 mm in the case of tendons and by 2-3 mm in the case of braids.

Blocking systems at the extremities of the stand, respectively extremities of the metallic frames, shall be placed in order to ensure that the maximum deviation of the reinforcement from the last distancing screen does not exceed an 1/10 slope.

In order to enable positioning of non-pretensioned reinforcements, pretensioning is allowed in two stages. The pretensioning force in the first stage shall be established depending on the adopted execution technology, but is shall not exceed 40% of the prescribed control force. Non-pretensioned reinforcements shall be mounted, positioned and bound with soft black tendon, and after these operations are completed, definitive/ permanent pretensioning can be performed in order to obtain the control force.

Positioning systems whose metallic pieces reach the surface of the concrete are forbidden, both in the case of pretensioned and that of non-pretensioned reinforcements.

In the case of pre-elongated reinforcements produced under the shape of bars, bound by screwed sleeves, the bar sections shall be marked and mounted in a previously verified order; screwing lengths shall be verified before pretensioning.

If reinforcement binding/ joining systems are used, then these systems shall be placed so that they allow free reinforcement elongation and they do not entrain the frames during pretensioning. The respective systems shall have a resistance capacity at least equal to 92% of the bound reinforcement breaking force/breaking resistance.

Manufacturing post-elongated reinforcements

During tendon, braid or bar cutting, in order to manufacture the post-elongated reinforcement, various tools and systems shall be used, which do not deform their extremities, preventing deterioration of the casings when the reinforcement is introduced into canals, as well as in order to enable correct execution of subsequent operations (production of the bulbs, mounting various advance devices/ systems etc). All necessary precautions must be taken precautions must be taken precautions must be taken be taken so that the steel is not contaminated with soil, grease/ fat, and so that it is not bent or scratched during cutting and execution of the reinforcements.

In the case of bundles whose tendons are blocked into the anchorage systems before pretensioning, removal of the temporary protection layer is not necessary.

In the case of other bundle types, the temporary cover/ protection layer shall only be kept/ preserved if essentially necessary because of the corrosive environment, or if the tendons can be degreased in the joining area into the presses or in the permanent anchorage systems.

The minimum measures to be taken during manufacturing/ execution and positioning, in order to avoid degradation pf the permanent reinforcement protection layers, shall be indicated by the reinforcement manufacturer or by the designer via the technical specifications; the constructor shall adapt/ adjust the reinforcements and shall complete them depending on the used working technologies.

The bundles as well as individual braids are executed in permanent central workshops of units specialized in prestressed concrete works, in temporary onsite workshops, or by directly pushing the reinforcements into canals, progressively unwound from/ out of the bundle; that the reinforcements are successively cut (if the applied procedure allows this operation).

Workshop equipment will depend on the average production capacity, as well as on the type of bundles to be executed. Appendix 5 indicates the features of equipment that may be used in the workshops of bundle production, with the characteristics presented in appendix 4, or with similar features.

The bundles and the individual braids executed in central workshops shall be accompanied at delivery by a quality compliance certificate, which shall contain the number of the quality certificate for tendons that make up the bundle/ bundle, respectively the braid.

The cutting length of the tendons that make up the bundles indicated in appendix 4 shall be determined by adding the minimal length values indicated in items 25, 26 of the table in appendix, to the length of the bundle between the anchorage support surfaces. If the cutting is to be performed with the welder/ welding device, then at least 30 mm must be added (temperature-influenced area).

Parallel tendon bundles (appendix 4), anchored in a circular section (ring-cone anchorage systems) shall be executed without ordering elements (spring or stamped rosettes)

The tendons shall be assembled into bundles using soft tendon bundles with a 1.5 mm diameter, at the extremities, and at distances of approximately 200 mm. It is recommended that the tendons are ordered at the extremities of the bundles, by successive and continuous binding with tendon approximately 1 mm in diameter. Intermediary tendon bindings can be eliminated or reduced in number, through helical twisting of the bundle, with a 250 mm pitch. All tendon bindings shall have the extremities bent towards the interior of the bundle, in order to enable introduction into cases. Intermediary tendon bindings can be eliminated.

For bundles different to those indicated in appendix 4, the data concerning execution of post-elongated reinforcements (requirements, performance criteria) must be included in the design (technical specifications) based on technical agreement data.

In case bundles made of different SBP lots, the bundles must be appropriately marked/ labelled and the bundles must be stored according to type.

For transport and haulage, the bundles that are not introduced into cases can be rolled with manual or mechanical systems (appendix 5). Rolling diameter should be at least 2,100 mm in the case of bundles made of tendon 5 mm in diameter, and at least 2,300 mm in the case of bundles made of tendon 7 mm in diameter.

Bundles introduced into polyethylene pipes can also be rolled; in this case the rolling diameter shall be determined by the rigidity of the pipe and by the number of tendons within the bundle; the diameter shall be established by performing several tests.

Rolling diameter of bundles in special plate cases shall be indicated by the manufacturer of by the unit that elaborated the prestressing procedure, using the respective bundles.

Execution of the canals for post-elongated reinforcements

The canals where post-elongated reinforcements are introduced shall be executed in compliance with design provisions, by embedding flexible steel plate cases, plastic cases of steel cases with thin walls. . For the procedures indicated in appendix 4, the canals (which can be coated of not coated) shall be executed in compliance with data in appendixes 4 and 6.

Canals and cases necessary in the precompression procedures used un the country must meet the following main requirements:

- ensuring that the appropriate curvature radius is obtained, in compliance with design provisions.

- the transversal rigidity of the cases shall comply with requirements from the execution stages; the thickness of the plate shall be minimum 0.2 mm for small-diameter cases, and it will increase to 0.6 mm for cases with a large diameter.

- the ratio between the diameter of the canal and the diameter of the bundle must allow introduction of the pretensioned reinforcement and injection of the cement suspension under optimal conditions; the interior diameter of the case must be at least 10 mm longer that the bundle diameter, while the interior section area of the case shall be at least twice as large as that of the reinforcement.

- proper binding must be obtained with the funnels at the extremities

- appropriate waterproofing of the reinforcements

- appropriate marking/ labelling, packaging, manipulation, haulage and storage

Use of plastic cases is only allowed for elements that are not calculated under strain conditions, and only if temperature during exploitation does not exceed +40C. No thermal concrete for concrete hardening shall be used for these cases. If the plastic cases have transversal undulations in the interior and in the exterior, then the restriction concerning elements calculated under strain condition can be discarded.

The canal/ case indicated in the design shall only be changed upon designer approval.

Cases with increased transversal rigidity shall be used in case execution conditions/ circumstances impede on placing the respective cases, introducing the bundles, casting and compacting the concrete etc. cases with increased

More rigid cases and as few joining points as possible shall be used when the thickness of the concrete cover layer or when other conditions do not allow subsequent intervention for unblocking the case area obstructed after/ during concreting.

The joints (T-joints) for injection and ventilation, places in compliance with provisions in chapter 8, shall connect the cases coating the canal so that they do not reduce its interior diameter. A possible solution is using a sleeve or a semi-sleeve, equipped with a piper for injection/ ventilation, to be applied over the case; the sleeve shall be pierced before injection with an appropriate tool introduced into the pipe. In the case of elements made of several sections, the connections can be placed into the joints between the sections.

All joinings between the cases must not allow relative displacement during the various technological operations (introduction of the bundles, concreting). For this purpose, exterior sleeves similar to cases can be used, as well as sleeves place/ fixed with adhesive band or other safe systems.

Socket coupling (mother-father sockets) of the plastic cases shall be performed in the same direction on the entire length of the canal in order to enable introduction of the bundles (from the father-socket side).

In the absence of design data, the deviations of case position in reference to the design route shall be confined within the following limits:

a) On the direction of the height of the element (h):

- for height up to 200 mm *) 0.02 h

- for height values 200-1000 mm 5 mm

- for height values > 1000 mm 10 mm

b) On the direction of the width of the element:

- width up to 200 mm 5 mm

- width between 200-1000 mm 10 mm

- width > 1000 mm 20 mm

*) In the case of the cases placed at the edges of the element sections, these deviations shall be considered on the respective direction, without the counterpart negative values.

In the case of several bundles, individual deviation limits can be exceeded (except for those at the extremity of the section) if the resultant force of the canal weight/ gravitational centres complies with the respective limits.

In the case of canals made of prefabricated blocks to be assembled, deviations at the extremities of a joint shall not exceed 3 mm for the root of the same canal. If the difference between the bundle diameter and the canal diameter is bigger than 15 mm, or in the case of joints wider than 100 mm, the deviations shall not exceed 5 mm.

In the case of canals made of prefabricated blocks to be assembled, deviations at the extremities of a joint shall not exceed 3 mm for the root of the same canal. If the difference between the bundle diameter and the canal diameter is bigger than 15 mm, or in the case joints are wider than 1000

The positioning systems of the cases shall be manufactured and placed in compliance with provisions of the design or with the details drawn up by the manufacturer and approved by the designer.

The devices/ systems can be independent or combined with elements comprising the non-pretensioned reinforcement, on condition that their assembly errors do not negatively impact on placement precision of the cases.

The distances between the support points shall range between 500 and 1,500 mm, depending on the longitudinal case rigidity. In the case or extracted cases, the distance may be increased to 2,000 mm. Larger distances may also be used, upon prior testing.

Positioning systems must be placed in sections where the curve direction of the alignment changes..

The horizontal elements that support the cases shall be manufactured from OB37 bars, steel flat strips, profiles, selected depending on transversal case rigidity. Usually, OB 37 bars with a diameter of 10-14 mm are used. For cases made of plate sheets with seams/ rabbets/ half-grooves or made of polyethylene, without any bundles/ bundles during concreting, the support surface of the case on the distancing device/ system shall be larger, in order to avoid transversal deformation.

Positioning systems must also prevent ascendant displacement/ movement of the case-bundle ensemble/ unit, because of its floating tendency during concreting and vibration/ ramming/ hammering.

Case positioning systems whose metallic pieces reach/ touch the concrete surface are forbidden.

In extremity areas, the axis of the canals (coated or uncoated) shall be perpendicular on the anchorage support surface, on the length indicated in the project/ design or in the specifications of the prestressing processes. For the processes indicated in appendix 4, this length value is 400 mm.

Mounting the post-elongated reinforcements

In the case of canals coated with plate sheet cases, as indicated in table 6.1 and 6.2 of appendix 6, or with plastic cases, it is recommended that the bundles be mounted before concreting, thus increasing transversal and longitudinal case rigidity.

The above-mentioned recommendation shall be correlated with provisions concerning temporary protection of the bundles (chapter 8).

Moreover, during cold seasons with high humidity, other procedures shall be adopted (if necessary) for increasing case rigidity (steel bars or pipes, smaller diameter plastic pipes etc); after that the bundles shall be introduced.

The bundles shall be introduced by pushing or by pulling.

The advance extremity of the bundle shall be equipped with a conic piece, anchored to the tendons of the respective bundle.

In the case of braids/ braiding, the bundle is mounted by successively unwinding the component elements directly from the bundle, and the extremity of the bundle shall be protected with a conic piece. This procedure requires that the braid/ braiding may be unwound from the interior of the bundle.

In the case of heavy bundles, with a vertical direction of with a high inclination,

brake drum systems are recommended for use (appendix 5), so that the bundle may be taken out again if necessary.

Before the formwork is closed, the state and position of the cases must be verified; this process shall constitute a stationing point, for which a hidden works report shall be issued, concerning the following:

a) the constructed route, which should comply with the limit deviations in reference to the design provisions.

b) Parasite deformations (winding) in a horizontal or vertical plane, between the support points; these deformations may cause additional friction that was not envisaged during the design process.

c) Deteriorations (cracks, holes, tearing) of the case that have not been repaired

d) Imperfectly sealed case joints.

e) Mounting of the joints for injection and ventilation

In the timeframe between mounting of the reinforcement into the canals and the start of the pretensioning and injection operations, the apparent extremities of the bundle must be protected (with bitumen-coated cardboard, plastic cases, etc), and the section o the bundle at the exit of the canal shall be sealed/ waterproofed, in order to avoid corrosion and penetration of the water into the canals.

4. ANCHORAGE, BLOCKAGE/ LOCKING SYSTEMS

The anchorage and blockage/ locking systems for prestressing are usually considered a component part of the prestressing procedure, together with the prestressed reinforcement used.

The anchorage systems for post-elongated reinforcements and blockage/ locking systems for pre-elongated reinforcements shall have a resistance capacity at least equal to the characteristic breaking force of the pretensioned reinforcement, without significant deformations of the component pieces.

The bundles indicated in appendix 4 are anchored with the anchorage systems indicated in appendix 7.

Other anchorage and blocking systems are used base don technical agreement.

Anchorages with loops and mandrels (appendix 7- fig. 7.6.) shall not be used as elements subjected to the wear and tear phenomenon.

Anchorages with loops and mandrels should be introduced into special recipients, filled with concrete or mortar for protection, over which cast-in-place concrete shall be applied- properly anchored by the extremity of the bundle and appropriately reinforced.

Pre-elongated reinforcements shall be anchored with homologated or technically agreed blocking systems, appropriate for the various reinforcement types. Appendix 8 offers an informative example of locking system for pre-elongated braids 7φ4 mm (TBP12).

In case individual braids are used as post-elongated reinforcements then corrosion-resistant anchorages (blocking systems) must be used.

Several technologies specific for various elements (tubes, pillars, cross-beam etc) require special anchorage procedures, to be approved/ homologated separately or together with the respective technological installation.

Anchorages for bundles made of SBP φ 7 mm, based on execution of bulbs at the extremities of the tendons, shall meet the following acceptance conditions as far as the bulbs are concerned:

- diameter  10.6 0.3 mm

- height  7 0.3 mm

- eccentricity max 0.3 mm

- sum of the openings of the fissures max 1.5 mm

- at least two fissures inclined at more than 30 degrees in reference to the axis

- no fissure must be inclined at more than 60 degrees in reference to the axis

Bundles are accepted if no more than 5% of the number of bulbs fails to comply with the above-mentioned requirements.

The bundle anchorage systems can also be used without homologation, by embedding one of the bundle extremities into the concrete, based on tests performed by a specialized institute or by a laboratory certified for testing in this particular field, and based on approval from the expert (specialist in the respective field).

In the case of elaboration of the technical agreement for pre-elongated reinforcements, safety of the anchorage, under the effect of vibration, for concrete compaction.

The component parts of the anchorages and blockages shall be manipulated and kept under appropriate conditions, in order to avoid deterioration or corrosion.

Based on periodical verifications, blockages which no longer comply with requirements concerning safety of pre-elongated reinforcement anchorage and which exceed the limit displacement limits during blocking, shall be eliminated.

5. REQUIREMENTS AND PERFORMANCE CRITERIA CONCERNING CONCRETE FOR ELEMENTS/STRUCTURES MADE OF PRESTRESSED CONCRETE

The concrete used for production of prestressed concrete elements and structures must meet the following specific requirements:

ensuring the minimum class:

o       C20/25 in the case of elements with pretensioned reinforcements made of mars with R≤590 N/mm2 and R≥890 N/mm2

o       C25/30 in the case of elements with drawn pretensioned reinforcements (tendons, braids, stranded tendon)

ensuring contraction and slow flow characteristics as reduced as possible, so that tension loss in the pretensioned reinforcements is kept to a minimum.

Ensuring a chloride content below 0.2% (in reference to the cement mass), because of the corrosive action of the chloride on the pretensioned reinforcement; additive solutions containing a larger chloride quantity that drinking water should also be avoided.

Enduring appropriate and constant compaction within the entire element (structure)

Concrete treatment and placement shall take into account the following specific provisions:

a) In the case pervibrators are used for concrete compaction, the following measures shall be taken in order to avoid contact of the pervibrator with the pretensioned reinforcements or with the cases used in construction of the canals:

the pervibrator introduction points shall be clearly and visibly marked;

special construction devices shall be placed in the points where the pervibrator is being introduced (such as metallic cases, bars, clamps/ cross-ties), in order to prevent contact of the pervibrator with the cases for post-elongated reinforcements

b) great attention shall be granted to concrete compaction in anchorage areas of the pretensioned reinforcements, in order to obtain the best possible filling, without deteriorating or displacing the reinforcements and the pieces embedded into the concrete; use of interior and exterior vibration/ hammering/ ramming are also recommended in these areas, for the same purpose.

c) In the case of pre-elongated reinforcements, executed with the stand/ stend technology, concreting shall be performed continuously, so that no more than 45 minutes pass between the casting of the first element and the end of compaction of the last element in the stand, at working temperatures below 30C, in order to preserve adherence of the reinforcements into the previously cast elements. At working temperatures above 30C, appropriate measures shall be adopted from the design and from technological files.

d) During removal the fresh concrete of pieces necessary for formation of various holes, or during thermal treatment, occurrence of cracks along the reinforcements shall be avoided as they will impact on adherence and on anti-corrosive protection.

e) After concreting is finished, the reinforcement bundles introduced into the cases should be moved in order to reduce the blockage effect resulted from possible deformation of the cases or from penetration of cement milk, but in such a way as not to cause displacement of dislocation of the cases. The joints located in minimum level points shall also be opened (where necessary) and water and impurities shall be eliminated through air blowing.

f) During concreting and hardening treatment, the protection measures for the reinforcements with permanent protections shall be established based on manufacturer recommendations.

g) During concreting, the cases without bundles shall be verified, by moving a cone piece into the case: the cone piece diameter shall equal that of the device to be installed in the advance extremity of the bundles, when the respective bundles are being mounted.

In case of constructions manufactured through gliding, this verification shall be performed immediately after the element is taken out of the gliding formwork, in order to ensure timely intervention, from the inferior formwork platform.

h) The prestressed concrete elements or constructions shall be de-centred only after they have been prestressed (partially or totally, in compliance with design provisions).

i) No hardening acceleration treatments shall be applied to elements comprising canals coated with plastic materials.

j) In the case of elements with pre-elongated reinforcements, the temperature shall not exceed 60C, and the cooling period shall allow decrease of element temperature to 20C before the prestressing force/ effort is transferred.

k) The reinforcement shall be protected against contact with steam or with wet materials used for concrete treatment.

The following provisions shall also be taken into account during elaboration of the schedule of concreting works- provisions referring to the time limits between the moment the reinforcement is hauled from the storage facility to the working point, and until execution of its final protection of the reinforcement:
a) In non-aggressive areas or in areas with very weak aggressiveness, the reinforcement shall be placed, pretensioned and protected in maximum 60 days, on condition that no more that 15 days pass between pretensioning and manufacturing of the protection layer. In the case of pre-elongated reinforcements, the pretensioning interval during concreting should not exceed 48 hours.

b) In areas with a weak aggressiveness as well as areas located 500-5000 m away from the shore of the Black Sea, reinforcements not protected via a temporary protection solution hall be placed, pretensioned and protected in maximum 15 days, on condition that the final protection layer be produced in maximum 5 days after pretensioning. The reinforcement whose temporary protection layer (oil emulsion) can be maintained until production of the final protection layer; the interval can be increased to 45 days, on condition that the final protection is made in maximum 7 days after pretensioning.

Environment aggressiveness shall be considered as indicated in normative C 170-87. 

In extraordinary cases, when, through the design solution, the intervals specified at item 5.3 cannot be observed (for example in the case of bundles introduced into canals before concreting and tensioning in various execution stages of the works), appropriate measures shall be taken in the design in order to use pretensioned reinforcements with permanent protection.

6. EXECUTION OF JOINTS FOR ELEMENT OR CONSTRUCTIONS MADE OF ARCHBRICKS OR PRECAST PANELS, ASSEMBLED VIA PRESTRESSING

The joints between precast elements (arch-bricks or panels) can be filled as follows:
a) Concrete casting in wide spaces (100-200 mm)

b) caulking or mortar injection into the joints 15-30 thick for elements up to 1.50 high, and 35-55 mm thick for elements higher than 1.50 m)

c) Gluing with epoxydic resins, in which case the thickness of the joints shall not exceed 1 mm; the resins shall be used based on technical agreement and of manufacturer provisions;

d) Other special methods, based on technical agreement

Filling methods can be combined for the same joint, for example: injection or casting with vibration (in the area containing canals) and caulking in the other areas.

Manipulation, haulage and storage of precast element shall be performed in strict observance of design provisions concerning position of the joining points, position of the support/ retaining points, as well as manufacturing methods for the lifting device.

Precast, prestressed elements or that of elements to be assembled through prestressing shall be stored on especially designed platforms (concrete, flat ground), so that settlement and contact with soil or other materials are avoided.

The arch-bricks or panels to be assembled by prestressing must meet the following requirements:

a) Each piece must be accepted and must comply with design provisions;

b) The relative position of the canals (coincidence, continuity) must be ensured

c) The sides of the joint must be correctly executed and their surfaces must not have cracks, fissures or scratches.

The joint execution process must comply with the following requirements:

a) Providing the connection between the material in the joint (concrete, mortar) with the concrete of the arch-bricks; this connection is ensured by indentation of the surfaces, reinforcement barbs, as well as by reinforcing the points with nets (netting the joints).

b) To ensure the waterproofing conditions (the shape of the joint must enable application of the material or that of the filling kit)

c) The sizes of the joint must enable joining of non-pretensioned reinforcements to the concrete under appropriate conditions.

d) The resistance of the concrete in the joint shall be in the immediately superior class compared to resistance of the concrete in the elements; maximum aggregate size shall not exceed 3 mm for joints up to 25 mm thick, and 7 mm for joints thicker than 25 mm; quality control of material in the joints shall be performed at the date when prestressing is initiated, and 28 days after casting of the joints, using the following:

prisms 40x40x160 mm or cubes (l=70.7 mm), for mortar

cubes with the l= 100 mm or 141 mm

e) the length of the welding seam or the reinforcement loop in the joint must observe the tolerance limits stipulated in the design.

The continuity and waterproofing of the canals into the joint can be obtained through the following alternative solutions:

recoverable sleeves made of rubber or other materials

irrecoverable sleeves made of plate sheet, polyethylene or PVC

Before the elements are assembled, the arch-bricks or precast panels shall be placed on support structures (stocks, platforms, non-settling foundations), which enable shortening of the element (displacement of the element) during prestressing and easy decentering of the intermediary support structures; special attention must be granted to the extremities of the support structures, which must take over the net weight pressure of the entire element without causing important irregularities.

Before assembly, the arch-bricks or the precast panels shall be thoroughly examined again, in order to make sure that their quality complies with design requirements. It is also necessary to verify that the real element length is consistent with the length indicated in the design.

Before placement of the arch-bricks or the panels into the assembly position:

- dust, dirt and any superficial layer of cement milk on the sides of arch-bricks or panels facing the joints, by tendon brushing and washing

- the state of the canals shall be verified (obstruction, cleaning)

- Safety during rolling shall be analysed both for the panels and for the entire element, and the appropriate support measures shall be taken to prevent shortening of the element during the prestressing process. Paddle work conveyor

After the arch-bricks or panels are placed in their assembly position, and before the joints are filled, measures shall be taken to avoid contamination of the interior sides of the joints and canals/

Before filling the joints with cement-based mixtures, the respective sides of the arch-bricks or panels shall be wetted; appropriate measures shall be taken to remove water from the base of the joints.

The composition and consistence of the joint filling material shall be established through preliminary tests.

Use of the additives is based on technical agreement; onsite preliminary tests are nevertheless mandatory; simultaneous use of two additive types must be approved by a certified laboratory.

Mortar compaction into the joint is generally performed by ramming it with a strip or with a metal rod. In order to obtain better compaction, each of the panel sides may contain a semicircular alveolus, which allows introduction of a pervibrator into the joint, when the joint thick. If the interior compaction method is used for mortar and concrete, then the compaction means/ equipment must not deteriorate or displace the sleeves needed to fit the canals into the joints.

After casting, protection measures for the joints must be taken, against rapid hardening (in case of excessively high temperature conditions), as well as against freezing (in low temperature conditions). 

REINFORCEMENT PRETENISONING

Pre-elongated reinforcements

Reinforcement pretensioning shall only be performed with homologated installations/ equipment, by teams certified in the field, as indicated in item 1.10.

The features of the equipment for individual reinforcements, elaborated by INCERC and homologated in Romania, are indicated in Appendix 9.

The equipment shall be used in compliance with manufacturer indications and with technological execution rules or the prestressed concrete element.

Special equipment, homologated by the suppliers, shall be used for prestressing cylindrical recipients by wrapping then with tensioned tendon. This prestressing procedure with the abovementioned equipment requires technical agreement.

Imported installations shall be subjected to technical agreement, as per Govt. Decision No 1046/1996, and they shall be guaranteed by the supplier and tested to their maximum capacity by the user.

Reinforcement pretensioning shall be usually performed at temperatures above 5C. In the case of pre-elongated reinforcements, the temperature can be reduced to 0C.

During periods with cold weather conditions, the pretensioning stage shall be correlated with meeting the necessary temperature requirements for the following operations, especially in the protection via injection.

In the case of elements executed on the stand, the environmental temperature difference between concreting and tensioning shall not exceed 15C.

For installations where the pretensioning force is determined based on pressure, the following requirements must be observed:

a) The gauges shall be hauled, manipulated and stored with outstanding care/ attention, in order to avoid shocks.

b) Apart from the working gauges, at least once a week a series of spare gauges shall be used. Special attention must be granted to correlation of the values for gauges graded in bars and those graded in atmospheres.

c) Besides the working and the spare gauges, a reference gauge shall be used for periodical verification of the working gauges.

d) The working gauges shall be verified at least once a week, and immediately after a gauge has been subjected to shock (e.g. the reinforcement drops down from the press, or the gauge is hit/ damaged); verification shall be performed by parallel assembly of the working and the reference gauge. The reference gauge grading shall be verified at least one a year, as well as in case of accidents occurring during transport or during use of the reference gauge.

e) It is recommended that the gauges used have the following characteristics:

working gauge class should not exceed 1.6, and in the case of reference gauges, maximum 1

the diameter of the display should not exceed 100 mm, and the minimum division should be 10-bar (10 atmospheres), in order to allow a reading of the pressure as accurate as possible.

The maximum allowed pressure of the gage should be at least 30% higher than the working pressure

The gauge should be of an anti-shock type, containing glycerine or other mechanical or hydraulic protection system.

For installations where the reinforcements are pretensioned in a group/ together, special measures shall be taken in order to preserve uniformity of the stress within the reinforcements (for example compensation cylinders of INCERC type, poly-cylindrical presses, previous stretching of each reinforcement, with a stress of at least 0.1 the value of the control/ reference stress, etc)

The reinforcements shall be blocked with special blockage systems for according to the used pretensioning installation, and in compliance with provisions of chapter 4.

Apart from verifications during acceptance, the pretensioning installations shall also be verified at least quarterly, establishing the correspondence between the installation measuring system and the generated force. Verification shall also be performed after any replacement of any installation component as well as anytime anomalies are discovered (different elongation values than calculated, deep scratches on the surface of the piston/flask, heavy pressure during backlash movement of the piston etc).

The precision class of the verification equipments systems should be equal to or below 1.

The equipment shall be verified at the start of each work shift.

The pretensioning program/ schedule, which is included into the technological file, shall comprise the following data:

Identification (element type, schedule elaboration date)

Technology used (bearing framework, stand)

Type and characteristics of the pretensioning equipment

Pretensioned reinforcement type

Pretensioning force established in the design

Tension loss, determined in compliance with indications at item 7.8

The pretensioning force to be obtained, taking into account the measured tension losses.

Control values at various time intervals (either after pretensioning, or before execution of the transfer), mutually agreed by designer and constructor, needed for the verifications indicated in 7.12, as well as the possible variation limits, taking into account the effect of stress decrease into the pretensioned reinforcement; the allowed deviations in the case of the pretensioning strain/stress obtained via hydraulic presses, are 3% for the average of strains in all reinforcements, and 5% for one separate reinforcement.

Design provisions and technological factory regulations shall be taken into account during verification of tension losses, necessary in order to draw up the pretensioning schedule.

Determination of respective losses (until the transfer stage), should be assisted by a specialized institute or laboratory with the appropriate equipment.

Technological conditions must comply with current production conditions.

At least 3 measurements shall be made on the same technological line, during difference technological execution cycles; the average value shall be taken as a reference in the calculation.

If the obtained pretensioning force, taking into account the losses determined as indicated in the previous paragraph, does not differ from the design value by more than 3%, then no corrections are necessary.

If there are bigger differences, then the appropriate measures shall be decided together with the designer and the expert.

Before pretensioning the reinforcements the following shall be verified:

- the appropriate blockage systems must be installed

- the diameter and the position of the reinforcements into the locking systems and into the positioning screens/ frames comply with the design.

- the safety devices of the pretensioning installation/ equipment (e.g. pressure limitation valve) are adjusted to the prescribed value.

- the various components of the pretensioning installation, especially the joints of the hydraulic installations/ equipment shall be operational and shall comply with the operation schedule.

- the support piece of the press is appropriate for the blockage type used.

- in the case of single-tendon pretensioning installations, the reach of the blocking/ locking piston must enable appropriate pressing of the wedges of the blocking system, after the proper control force has been reached inside the reinforcement

- all work safety measures must be observed

- all proper conditions must be ensured for technological operations to be performed as required by the provisions of the technology to be used in the pretensioning program and in due time; the reinforcements must not be kept long in a tensioned and non-concreted state;

Pretensioning of the reinforcement shall be performed in compliance with the established schedule; the components of the pretensioning installation must be assembled similarly as during the tests performed in compliance with item 7.6, without introducing any additional sources of tension loss (faucets, pipes with narrow sections etc).

Pretensioning of the reinforcement shall be performed in compliance with the established schedule; the component of the pretensioning installation must be assembled

The strain in the pretensioned reinforcement shall be achieved, maintained within the required limits and controlled by engineering personnel qualified in the field, based on an observation and measurement program, which, apart from tests on the installation and on the gauges (indicated in 7.4 and 7.6), shall at least comprise the following operations:

a) Measurement of reinforcement displacement/ gliding for each blockage, at least once every two weeks. The recorded values should normally be within the limits prescribed in the design of the element. The respective values may be exceeded (by maximum 50%) only in the case of reinforcements longer than 18 m.

It must be established whether the displacement/ gliding values are caused by inappropriate operation of the pretensioning installation- e.g. lack of, or insufficient, pressing of the wedging during the blockage/ locking procedure.

b) Verification of the strain in the pretensioned reinforcement shall be performed periodically, via survey, for at least 10% of the number of pretensioned reinforcements.

Measurements should be performed at a constant interval of time, for all reinforcements. The respective interval shall comply with provisions of the pretensioned program/ schedule and with the measurements performed as indicated in 7.8.

In case the measured values are not within the variation limits allowed by the pretensioning program, the causes shall be analysed and deficiencies shall be eliminated; if necessary, the pretensioning program will be updated. The elements in whose case the pretensioning force is in doubt shall be subjected to examination; after that, a decision shall be made on how the elements are going to be used.

In the case of individually pretensioned reinforcements, these verifications can be performed by recording the breaking force of the blockage, with the help of the press, placed on an appropriate support.

During verifications, electro-resistant or hydraulic force captors should be used, with precision class 1, placed between the press and the bearing supports. Tests can also be performed along the reinforcements with the Vogt device or with a similar tested and approved grading device. In the case of reinforcements pretensioned with another system, such as continuous wrapping, verification shall be performed in various points along the reinforcement with measuring devices equipped with a vibrant shank (coada vibranta) of with prescribed/ imposed deformations (for example the Vogt device).

During verification, electro-resistant or hydraulic force captors should be used

Apart from verification indicated in item 7.11, other measures may also be adopted, especially in the case of special technological processes (intense vibration, centrifugal action etc), which may influence reinforcement blockage conditions/ requirements. In these cases, possible gliding/ displacement of the reinforcements during the various technological stages shall be periodically checked, though reference points drawn on the reinforcements, in order to eliminate faults/ deficiencies.

The data obtained after tests indicated at items 7.4, 7.6, 7.11 and 7.12, as well as those referring to the pretensioning of the reinforcements (for each element or group of elements) shall be obligatorily entered into a register, which is kept by the pretensioning team and which shall then be preserved for 50 years; the element manufacturing file/ sheet shall only contain data indicated in 7.14.

Execution units can also adopt other methods of recording and keeping pretensioning data, in compliance with their own quality assurance system.

Records concerning pretensioning, which shall be entered into the elements pretensioning file, must comprise data concerning the tensioning force, according to reinforcement types, and observations representing possible differences from the pretensioning program schedule.

The transfer operation performed only after verifying, through tests pieces kept under the same conditions as the element as indicated by STAS 1275-88, whether concrete resistance complies with design provisions. The transfer operation performed only after verifying 

The transfer operation should be performed slowly. In case the transfer cannot be performed slowly, but only by cutting the reinforcements (with silicon carbide disks, with special scissors or with a welding device), then the reinforcements must be cut in the order indicated by the design; the operation is performed alternatively from both extremities of the form or of the stand.

Post-elongated reinforcements

Reinforcements shall be pretensioned in compliance with requirements in items 7.1-7.3; the pretensioned installations produced by INCERC and approved in Romania are presented in appendixes 9 and 10. The working methods are detailed in the technical specifications of the respective installation.

Apart from tests performed during acceptance the pretensioning installation shall be verified as follows:

a) When brought onsite, the installation shall be tested at a pressure 5% higher than the maximum indicated working pressure. The test can be performed together with measurement.

b) At the beginning of each work shift the main components of the installation shall be verified (joints, pumps etc), also controlling whether the components are in a proper state and whether they are properly installed/ assembled.

c) When the installation is brought to the site, and after each change of the piston packing and every time the installation is interrupted for a month, the interior friction of each pieces must be measured, under conditions as close to the working conditions as possible (the liquid used, temperature, pressure).

Friction can be measured either with the appropriate force captors, with precision class I in both cases, before performing the measurements, the piston shall be moved 3 times on its entire range; the pressure variation interval is recorded and the average of the 3 measurements is calculated. This operation shall employ a low pressure gauge (approx. 20 bar).

a) In case force captors/ gauges are used, the pressing order is the following: the press to be verified, the ring of the blockage system, the force captor, the anchorage system used for locking the bundle/ bundle used in calibration

The value f of the friction inside the press is determined with the equation:

A= the surface of the transversal section of the press piston

p= the pressure at the gauge of the pump activating the press

F= the force measured with the force captor

The friction may be measured for forces up to 70% of the maximum force, and the results shall be extrapolated.

b) In case two presses are used, they shall be coupled head to head, through the bundle/ bundle to be tensioned; the rings of the anchorage systems shall be placed between the presses. In the case of 1200 and 2500 KN installation, blocking and unblocking valves shall also be assembled. Each press shall be attached to pump equipped with a gauge; only one of the pumps is activated (the active pump), while the piston shall be removed, and the pressure chamber closed, from the other press; the friction values f shall be determined with the equation:

the pressure indicated by the active pump gauge

the pressure indicated by the passive pump gauge.

Gauge readings shall be made only while the pressure is very slowly rising, or even when the pump stops, because when the pressure drops the friction acquires negative values.

Gauge readings shall be made only while the pressure is very slowly rising, or even when the pump stops, because when the pressure drops the friction acquires negative values.

The value f obtained in this case represents the average of friction values in the two presses; in order to increase precision, at least two measurements are necessary, with different stop points/ stages, so that, each press-pump installation must in turn be active.

Based on the data obtained, a graph shall be drawn up, which shows the real force of the press for the various values indicated by the gauge. It is recommended that friction losses be determined with precision class I gauges. Hand-operated pumps can also be used instead of electrical ones.

The following preliminary operations shall be performed for the element to be prestressed:

a) Verification shall be performed to make sure that all measures have been taken during execution, in order to allow deformation, during prestressing, in compliance with the static scheme adopted through design (e.g. a movable support for one the extremities of the beams, hinges for particular pillars in the case of frame constructions etc); moreover stability must be ensured for independent elements.

b) The anchorage systems must be accepted and must comply with verification requirements.

c) The steels the bundles/bundles are manufactured from must be checked for the quality compliance certificates.

d) The concrete shall be examined, particularly in the support area of the anchorage systems, so that no segregation, fissures or other defects or degradations occur. The position and diameter of the hole in the distribution plate shall also be checked for compliance with the type of anchorage used.

e) Controls must be performed to make sure that degradations impacting on the elements resistance capacity have been remedied; the duration necessary for the repair material to harden is also monitored.

f) The extremity of the bundle canal and the distribution plate must be perpendicular one on the other. In case perpendicularity is not obtained in all directions (with a maximum 3 deviation), then wedge-shaped metallic plates shall be used under the whole/ entire anchorage, in order to correct the respective deviations.

g) The appropriate test pieces shall be verified; they shall be kept under the same conditions as the concrete element, in order to determine concrete compression resistance. In the case of constructions with precast arch-bricks or panels assembled via prestressing procedures, quality compliance certificates issued by the manufacturer must be available onsite, in order to guarantee the required concrete quality. If there are doubts over concrete quality or in case of deteriorations of the elements during the prestressing procedures, non-destructive tests shall be performed in order to determine the effective concrete resistance.

In the case of elements assembled from arch-bricks, tests shall be performed on the test pieces, extracted from the filling material of the join; these test pieces shall be kept at the assembly place. The transfer resistance of the material in the joint shall comply with design provisions.

h) Formworks, scaffolds, and centrings shall be verified to ensure they can bear displacements during the prestressing procedure, as indicated in chapter 2.

i) Records concerning pretensioning, which shall be entered into the pretensioning file of the element, shall comprise data concerning the tensioning force, according to reinforcement types, findings and observations representing possible differences from the pretensioning program schedule.

The following preliminary operations shall be executed for the pretensioning reinforcement:

a) The state of the reinforcement and preservation/ protection methods for the reinforcements shall be verified.

The bundles that have a rust layer on the tendon surfaces can be kept inside the canals provided the rust layer is easily eliminated by cleaning the tendon with non-abrasive materials. In all other cases the approval of a specialized institute (laboratory) is required.

b) The section of the reinforcement shall be checked for compliance with design provisions.

c) Real friction losses shall be determined for a series of bundles with geometrical features as different as possible (length, angle deviation); these bundles are pretensioned as both extremities, so that it can be compared with the values envisaged during design, and so that the control value for the pretensioned reinforcement elongation is established. The determination method for real friction losses is indicated in item 7.22.

The designer shall process onsite the suggestions of the prestressing engineer, concerning the following:

a) The value of the control force, taking into account the real friction losses

b) The control elongation value of the reinforcement pretensioned for the unit control effort, taking into account the elasticity module of the reinforcement established as indicated in 3.8, and also considering friction losses, determined onsite. Elongation shall be calculated for the entire bundle length, including the sections up the anchorages de prindere in prese.

c) The special prestressing program, if the design indicates that prestressing must be performed in stages, taking into account the real conditions the respective operations are performed in.

In case of elements executed after typical designs the data indicated in paragraphs a, b and c shall be established together with the designer of the works.

The designer and the prestressing engineer shall establish the type and number of identical bundles that require measurement of friction losses.

More numerous measurements shall be performed in the case of important constructions, or constructions with special exploitation conditions (located in environments of average or high aggressiveness, subjected to action of liquids, gases, radiations etc. In case measurements are not performed on all bundle types, then rectilinear and curved routes shall be chosen/ selected in order to separate the linear friction coefficient K from coefficient .

In the absence of linear bundles, the friction coefficients can be separated as indicated in appendix 11.

In the case of bundles with ring-cone anchorage systems, the cone shall not be placed between the tendons during the friction measurement operation. The other additional pieces (locking and unblocking faucets) shall be mounted in the same manner as in the case of measurement of friction in the presses.

Friction losses shall be determined by use of two presses, one at each extremity of the bundle; pretensioning is performed with a single press (the active press), while the other press has its piston taken out and its pressure chamber sealed.

Based on pressure readings (p1 and p2) at the gauges of the two installations, the forces at the extremities of the bundles are determined, with the following equations:

- the force at the pulling extremity:

F1= A*p1 (1-f1)

- the force at the opposing extremity:

F2= A*p2 (1+f2)

A = the surface of the transversal press piston section

f1 and f2= interior friction coefficients of the presses, correlated to pressures p1 and p2.

In case friction inside the presses was determined by coupling of two presses, then f1=f2.

Tension loss (ΔF) cause by friction shall be:

ΔF = F1- F2

In case friction losses are determined using force captors, then the length of the bundles the measurements are performed on must be increased, in order to allow placement of the respective captors; the bundles shall be manufactured from the same batch as the current ones.

Friction losses may be measured by extrapolating the values obtained at a tensioning level equal to 85% of the control effort/ strain indicated in the design.

In case of very long route, when the elongation exceeds the depth of a press even at only 85% of the control strain/ stress, the measurements can be performed by successive gradual operation of the two presses.

In the case of braids from the same bundle, individually and successively pretensioned, friction shall be measured based on instructions from the elaborator of the procedure. All the braids belonging to the same bundle shall be verified, taking into account the variable transversal pressure of previously pretensioned braids, which leads to various degrees of losses into the braids.

The pretensioning program is finalized based on measurement results as per item 7.22. The program shall be updated in case of subsequent differences compared to the initially established losses. The program shall be updated if subsequent differences from the initially established losses are discovered

If for some bundles the friction losses obtained by direct measurement, or based on direct measurement, are higher than friction loss values indicated in the design by more than 3%, and the design control effort/ strain/ stress cannot be further increased (the strain is equal to 0.8 P), one of the following solutions shall be adopted:

- The control strain shall be increased for the other types of bundles in the element; the control effort for these types of bundles is, by design, smaller than 0.8 P (for example rectilinear bundles with small angular deviations)

- the number of tendons in the bundle shall be increased, if the element contains bundles with a smaller number of tendons than the maximum number allowed by the locking system

- Friction alleviation measures shall be taken, such as spreading a film of PE 1A emulsifier oil on the tendons.

If friction losses are lower and if they are certain to be maintained at the same level for all the other elements, then the possibility of reducing the control force shall be taken into consideration.

The measurement data, in compliance with items 7.18 and 7.22, as well as the pretensioning schedule/ program shall be appended to the file (diary?) of the works.

In the case of elements with post-elongated reinforcement, the press needed to stretch the reinforcement must lean against the element being prestressed, in order to achieve the elastic shortening of the concrete during the transfer.

Before installation of the press, the reinforcements that make up the bundle shall be arranged on the area stretching out of the concrete, so that they can be properly assembled in the inventory locking system, after introduction of the press. The piston of the press shall be operated in idle running in order to verify if friction inside the press are modified compared to the value determined as per items 7.18 paragraph 2.

The reinforcement shall be pretensioned until reaching the control value, in 4 or 5 stages. All data during each stage shall be collected, in order to accurately determine elongation and the pretensioning force. Appendix 12 details a model of how to draw up and complete/ fill in the pretensioning file, with the following recommendations:

a. The pressure of the pretensioning stages must correspond to divisions of the gauge display.

b. The first two stages must be equal one with the other, and must account for 1/6 of the final unit strain/ stress.

c. The diagram stress-elongation shall be represented on graph paper, in order to verify linearity of the elongation and the necessary extrapolation, as indicated in item 7.30.

The gauge indicators shall be read only when the pressure I very slowly increasing, or at the moment the pump is disengaged/ stopped, because during discharge the respective values/ figures are influenced by direction changes of interior press friction.

In the case of ring-cone anchorage systems, the pressing force exerted on the cone at the end of the pretensioning process shall range between 15% and 20% of the bundles breaking force (for 1250-2500 KN pretensioning installations), or between 18-22% (for 300 KN and 600 KN installations).

In special cases when the control force of the bundles cannot be achieved in one pretensioning stage, it is recommended that the first pretensioning stage represent 40-60% of the control force. Intermediary pressing of the cone should be performed with 70% of the final pressing force.

Al the data in the pretensioning files should be filled in directly during performance of the works. In case work conditions prevent this, the pretensioning data can be entered into a workbook, and the files shall be drawn up based on these workbooks.

The recorded data/ readings shall be processed before the anchorage systems are permanently blocked, in order to draw the conclusions over the prescribed elongation, in compliance with item 7.33.

The pretensioning files represent the sole valid act establishing the quality of pretensioning operations. The files are completed and signed by the engineer responsible for prestressing, and they shall be appended to the construction book.

In case of structures with a large number of bundles with similar features, individual files may be replaced with a common file for a group of bundles; the data are compiled into the appropriate table form.

The elongation of the pretensioned reinforcement is measured after the finalization of the first pretensioning stage, which is considered as the conventional zero stage and the value corresponding to the elongation corresponding to the interval between zero pressure and the pressure of the stage chosen as conventional zero is obtained via extrapolation.

Elongation of the reinforcement during pretensioning shall be measured with an 1 mm margin, as follows:

a. Measurement of the displacement of (bench)marks on the reinforcements, compared to the element extremity surface (the case of installations where the reinforcements are accessible, for example 300 and 600 KN installations).

b. Measurement of the displacement of the piston (in case of the INCERC 120 installation for bundles 24φ7 mm and INCERC 250 or bundles 48φ7 mm)

In case b, in order to establish the effective elongation, the obtained values must be corrected by decreasing the displacement of the reinforcements caused by the progressive wedging in the inventory anchorage system of the press.

Usually, the ensemble formed by the tendons and the cone of the inventory anchorage are simultaneously displaced, so that the displacement of the cone represents the correction value.

In order to timely discover occurrence of an exaggerated discrepancy of the stress/ strain in the reinforcements comprising the bundles, all the reinforcements shall after wedging into the inventory anchorage system of the press (near the anchorage pieces); these marking shall be monitored during the tensioning process.

If significant irregular gliding occurrences are discovered, (>5 mm), the bundles shall be taken out of the press by strapping (declavetare) of the inventory anchorage system, the bundle tendons shall be rearranged and the tensioning operation shall be restarted.

During the pretensioning procedure for each bundle, the effective elongation value corresponding to the unit control stress/ strain shall be compared with the elongation indicated in the pretensioning schedule. When pretensioning is performed at both extremities, the comparison is made for the entire elongation, which represents the sum of all elongations at each of the extremities; variations may occur between the values registered at each extremity, depending on the time if takes for the proper force value to be reached, on the bundle asymmetry etc. When pretensioning is performed

If the differences between the effective values and the control values are:

a) 5%- then the pretensioning operation is considered satisfactory

b) 5-10%- temporary increase of the unitary control stress/ strain is allowed, by up to 5% compared to the values indicated in the design, so that the measured elongation complies with the limits indicated in paragraph a.

c) +5+10%- additional gauge verification shall be performed; if gauges are found to be properly calibrated, then pretensioning shall be considered compliant/ satisfactory; before the gauges are disassembled for verification/ testing, it is recommended that the pressure be reduced by minimum 20%, in order to avoid excessive pressure within the installation.

d) Higher than 10%- the works pretensioning works shall be stopped and the designer shall be notified.

After pretensioning a certain number of identical bundles and after establishing the variation domain of the elongations, the causes for significant breeches of the respective domain must be identified/ determined.

Gliding/ Sliding of the tendons into the anchorage system during blocking, shall be determined when the pretensioning pressure is decreasing, after pressing of the cone by measurement of the displacement of markings drawn on the tendons of the bundle, in reference to a fixed point on the on the concrete piece or from the body of the press. In the case of installations whose reinforcements are not accessible (INCERC 120 and INCERC 250), reversion of piston shall be measured.

In order to establish the real gliding of the tendons into the anchorage system, the elongation of the tendons shall be deducted on the distance between the anchorage and the section where the marking was drawn, corresponding to the unitary control strain/ stress, from the length of the displacement measured as per the previous paragraph.

Gliding of the tendons from the fixed locking system, in the case of pretensioning from a single extremity, shall be determined by measuring the movement/ displacement of markings drawn on the tendons, in reference to the front side of the locking system.

If during transfer the tendons in anchorages with cones or wedges are displaced beyond the maximum value specified in the design or in the anchorage instructions of use by more than 50%, then the pretensioning works shall be interrupted and the anchorages shall be re-verified.

After the pretensioned reinforcement is fixed into the anchorages and after the press is removed, in the case of ring-type anchorages, a sign/ marking shall be drawn on the reinforcement approximately 100 mm away from the front of the anchorage, which shall be verified until the next day, in order to discover possible gliding/ deviations.

If there are such gliding deviations, then the pretensioning procedure shall be interrupted and the anchorages shall be verified again (geometry, roughness).

The edges of the tendons shall be cut at the moment when jetting preparations start. All operations shall be performed with great care, avoiding shocks and bending of the reinforcements, which might cause the reinforcements to slip out of the anchorages. The tendons shall be cut with rotating disks or with oxy-acetylene flame, at a minimum distance of 50 mm away from the anchorage. Any necessary bending of the tendons shall be performed with special keys; in this case the cutting length shall be increased. The extremities of the tendons need not be cut if concreting of the extremities allows embedding on the full length of the tendons.

8. PROTECTION AGAINST CORROSION AND ADHERENCE OF THE POST-ELONGATED REINFORCEMENT

General rules

The prestressed concrete elements and constructions with post-elongated reinforcement must be designed with a permanent protection system for the prestressed reinforcement.

Depending on the adopted prestressing procedure, the permanent prestressing could be:

a)      Adherence is made of prestressed reinforcement and concrete;

b)      Adherence is not made of prestressed reinforcement and concrete.

Grouting of permanent protection systems by application of materials (bitumen, epoxy resins, etc) other than stipulated under the Appendix 13 and other special grouting technologies (vacuumating) will be made on account of special regulation or type approvals that will also include the checking and acceptance terms.

The consistency of special materials shall not dislodge the respective materials if the pressure water infiltrates into the canals.

Regardless of the type of protection reinforcement on the route, the anchoring place will additionally be protected with mortar, concrete or synthetic materials, which will be designed both with appropriate link to the areas to be protected and high compactness degree.

Special care shall be paid to protection of the extremities of bulb or mandrel loop anchoring systems.

Temporary protections of the reinforcement to be maintained after performance of the permanent cement reinforcement will be stipulated in the technical specification, after the expert institutes (laboratory) makes the tests confirming that neither adherence nor protection against corrosion are affected.

The time periods for performance of the permanent protection will be set based on the item 5.3. During this period of time, reinforcement corrosion shall be prevented, by taking one or more of the measures below:

Prevention from water infiltration into canals;

Discharge of water accidentally infiltrated into the canals through the outlets in the minimum levels of the route as well as blasting of compressed air;

Protection by covering of the bundle outer section;

Exceptionally, when it is considered that the deadline for performance of protection cannot be observed, the designer will be asked for approval on the protection measures to be implemented.

During cold and wet seasons, the bundles shall not be brought into the canals prior to laying of concrete. Under these circumstances, measures will be taken to avoid corrosion of the steel sheaths.

The temperatures proper to perform the prestressed reinforcement protection will be within +5⁰C and +30⁰C.

In case these temperatures do not range within the mentioned limits, special measures to be endorsed by the designer shall be observed for the reinforcement protection.

The anti-corrosive protection systems of the prestressed concrete surface will be adopted and implemented according to the technical instructions C170-87 and to the part A of these practice guidelines.

Grouting

The composition of grouting mixture (cement paste) must be established based on preliminary tests undertaken by a certified laboratory in order to determine the parameters of the respective mixture. These parameters will be determined in accordance with the terms of the Appendix 13. The following rules shall be followed:

The tests will be made on two different cement samples, minimum, taken out from the supplied cement batch;

The same conditions shall strictly be reproduced (mixing, temperature, etc) for all mixtures;

The fluidity of grouting mixture shall be within 35-25 seconds. The limit of 35 seconds can be exceeded if it is sure that no obstruction occur (canals of reduced length, large diameters);

The minimum resistance to compression of the grouting mixture will be minimum 20 N/ mm² at 7 days.

Prior to grouting commencement, it is recommendation that the plant and all necessary spare devices (mixer, injection pump, hoses, etc) should be provided for a possible intervention to all bundles` access points.

The pumps and joints shall be tight so that air cannot enter the canal and obstruction cannot occur during grouting process.

The type and characteristics of Romanian products are detailed in the Appendix 5.

Procedures providing grouting with compressed air shall not be applied.

Preparation of anchorages for grouting shall follow the designers requirements.

The wire ends standing out of anchorages shall be cut in compliance with the requirements of point 7.36.

Prior to grouting commencement, the anchoring area shall be sealed either with mortar, concrete or epoxy resin or with a metallic cover and sealing set fastened on the metallic cover under the anchorage.

Both alternatives shall allow that connection of hose supplying cement paste shall be safe and tight as well as interruption of pressure circulation.

For this purpose either hose parts or plastic pipes (used for baffling at grouting completion) or valves can be used.

Before grouting, the canal has to be washed and pressure water or compressed air shall pass through oil filter to check its tightness and continuity. Washing will be more intense if the wires have been greased with emulsifying oil. These operations shall be undertaken at least 15 minutes prior to grouting commencement, in case of coated canals and at least 60 minutes in case of uncoated canals.

It is recommended to use compressed air to discharge the water if no drainage outlets have been designed in the lowest points of the canal.

The grouting mixture shall be brought into the horizontal bundles through:

Axis of anchorage for straight or slightly uneven bundles. Both uncoated canales over 30 m length and coated canals over 40 m length will be equipped with control intermediate, intervention joints or joints for continuation of grouting;

Grouting joints placed in the lowest point of the canal, in case of curve route bundles; the distance between bundles will not exceed 20 m;

In reference to right or inclined bundles, the grouting mixture will be inserted through the axis of the anchorage from the bundles lower side.

It is recommended that the bundles longer than 25 m should be designed with control filling or grouting joints if needed (for instance when the pump cannot be get the pressure required for the entire height of the canal).

The right or inclined bundles will be equipped with re-grouting joints placed between 1.5 and 3 m from the upper anchorage.

As for the bundles with one end anchored by embedding it in concrete, the grouting or control joints shall be placed to fill the area up to the contact with the concrete where the bundle is embedded.

In case of block elements, it is recommended to have at least one control joint on the route of each bundle.

When grouting mixture is inserted into the canals, the following rules shall be met:

a)      Grouting will be done with membrane, conveyer or piston pumps;

b)      Access to the canal will be continuous and slow (6-12 m/ minute) all joints along the canal will be unoccupied, at the beginning. Air shall not be inserted at the same time with mixture, while pumping. The joints will be filled while the mixture is getting closer.

c)      Depending on the grouting manner of the first bundles, the mixture fluidity might be reduced.

d)      After the mixture fluidity coming out through the first outlet is much similar to the initial one, this outlet will also be filled, and the pressure will be 3 bars higher than the mixture grouting pressure; this over-pressure will be kept constant for approximately 2 minutes, in case of coated canals and for approximately 3 minutes in case of uncoated canals.

In case of expansive additives, the over-pressure can be reduced to 2 bars for 1 minute. Under these circumstances, either porous plugs will be used to allow the discharge of water resulted from grouting or the joints will be filled later.

e)      The interconnected canals will be grouted simultaneously or in sequence without interruption; one must be sure that all canals have been filled completely.

In case of grouting mixture preparation, it is recommended to use delay additives to inject the mixture easily, switching from one canal to another.

f)       After approximately 45 minutes from grouting, re-ground is mandatory, following the same requirements as in case of grouting; the re-grouted quantity of mixture will be maximum 10% from the grouted quantity (before the pump connection, the access will be scoured with an appropriate metallic rod).

Re-grouting may be given up if some proper additives are used.

g)      Special joints (see point 8.12) will be used for re-grouting of vertical or inclined bundles. Re-grouting should be used even in case of some expansive additives.

Re-grouting will be performed after 45 minutes from the completion of grounding. It is recommended that the first grouted canals shall be applied two or three re-grouting, at different time periods, to establish the optimum re-grouting time period; after that the effect of grouted mixture sedimentation becomes negligible. Under exceptional circumstances, when re-grouted could not be done through the special joints (see point 8.12), the respective operation will be done through the axis of the upper cone, allowing the discharge of water from the upper side.

The quantity of mixture brought while re-grouting will not significantly exceed the quantity needed to fill the void due to sedimentation.

h)      At approximately 24 hours after completion of grouting, all remained voids of the outlets on grouting vacuuming or control joints will be filled with cement mortar up to the concrete surface or to the end of the pipe. Special care shall be paid to grouting of bundles with high dips at the ends and vertical bundles.

The metallic pipes of access joints will be removed or protected so that the concrete shall not be damaged by corrosion.

The following tests shall be carried out to control the grouting mixture quality, as per the Appendix 13:

Determination of fluidity of each mixture batch;

Determination of sedimentation and resistance to compression once for all bundles grouted during a shift, in the same conditions;

The results will be recorded in the grouting sheet prepared in accordance with the Appendix 14.

Grouting during cold weather

If during grouting and hardening of mixture, the air temperature is be below +5⁰C, the elements shall be protected from the outdoor environment, by means of some auxiliary constructions or utilities heated with warm air, warm water or steam pipes, infrared rays, electrical resistance, etc at minimum +5⁰C.

Grouting will be processed after minimum 48 hours since heating started.

Heating shall continue at least for 48 hours after finalisation of grouting, depending on outdoor temperature.

During heating, the temperature shall be measured every 6 hours; the respective values will be recorded in the remarks column of the grouting sheet.

In all cases, when grouting is done in very cold weather, it is recommended to use frost resistant mixtures, checked by laboratory tests, which confirm that there will be no increase in volume after they are kept 36 hours at +2⁰C -+5⁰C nor fast decrease at -20⁰C.

A pore load of 6-10% usually enables a frost resistant mixture.

It is recommended to take increased measures for the bundles to be grouted during cold weather to prevent water from entering the canals, involving all operations from laying of bundles to grouting. These bundles should be designed with outlets in the lower parts placed downwards or sideways so that the water can freely discharge.

If the water still infiltrates into the canals despite all measures compressed air must be used to discharge immediately the water. In all cases of compressed air usage, it has to be passed through the oil filter.

Before grouting, the canal continuity is checked to detect the possible blockings formed after occurrence of ice plugs; compressed air must be used for this purpose, because water is used instead, it is very difficult to discharge it from the clogged canals. It is forbidden to use steam for this operation.

If any ice plug is found, heated compressed air will be blasted into the obstructed canal and into the near (unobstructed) canals, until the canals continuity is provided (ice is completely melt). The air must leave freely through the opposite extremity. It is prohibited to blast electric current to heat the prestressed reinforcement.

On the grouting day, the canal walls shall be washed and heated, and any ice remainders shall be melt. The canals shall be filled with water heated at 30-40⁰C and will be kept in for approximately 15 minutes. This operation shall be repeated at least twice.

Warm water shall be brought into canals, which will certainly be grouted on that day.

If, exceptionally, some washed canals cannot be grouted on the same day, the respective water must be disposed entirely, using heated compressed air.

The stipulations of the Appendix 13 amended with the additional provisions below shall be respected at preparation and grouting of mixture:

Temperature of mixing water will be within +30⁰C and +40⁰C;

Temperature of mixture shall be minimum +20⁰C when it is brought into the canal;

Air entrainment additives that grow the additive pores load will be used to improve the frost behaviour.

The tests and documents under the point 8.17 have to be provided to control the quality of the grouting works done on cold weather.

Protection of outdoor prestressed reinforcement

The prestressed concrete elements or constructions, which prestressed reinforcement will be designed outer the section, shall be concrete adherent and the project must detail at least the way of concrete or mortar protection laying, the concrete or mortar brand, layer thickness, the waterproof level.

Concrete or protection mortar shall be continuous and compacted, as much as possible, (for instance for the waterproof level of concrete shall be at least P₈¹⁰); it is advised that the value of resistance and concrete in elements shall be the same, at least C25/20, respectively M300.

Thickness of mortar or concrete cover layer will be measured depending on the environments aggressiveness, in compliance with the requirements of the technical instructions C170-87 and part A of this practice guidelines.

Approval of expert institute or laboratory will be asked for with respect to the cases not included in this guidebook.

In reference to the elements which side opposite to the prestressed reinforcement is in contact with liquids or aggressive materials, measures will be taken beginning with the preceding pre-tensioning stages that the protection of reinforcement shall be proceeded after restoration of the concrete tightness. This operation can be renounced of only based on special regulations.

Injection of concrete provided to protect the outdoor reinforcement of elements or constructions shall follow the instructions of C1130-78 and the rules below:

a.       Only the cements mentioned under the point 1.3 to the Appendix 13 shall be used for preparation of mortar or concrete mixtures applied by injection procedure;

b.      The minimum open distance between the two adjacent wires as well as the thickness of protection layer shall be taken into account when the sort of sand grading and the maximum size of the aggregate grain are defined;

c.       Additives shall be used to prepare the mortar and concrete mixtures to be grouted to the prestressed concrete works;

d.      The surface shall be cleaned properly and blasted if needed; rust shall be removed from the reinforcement; after blasting, air jet will be applied to clean the surface. If the reinforcement has temporarily been protected eg with cement milk or other substances for temporary protection that reduce the adherence will be removed by the most efficient procedure (sand blasting, water jet or compressed air, etc). If the temporary protection is maintained, cleaning shall be done by the best procedures not to damage it.

e.       The grouting mortar applied to protect the reinforcement pressure wound on the recipients shall be injected after the respective recipients have been filled with water and all losses have been eliminated and if possible after the maximum water pressure in the pit have been obtained. The recipient will not be emptied until the grouting design resistance is not obtained. In order to enforce the terms under this paragraph without delay the grouting protection, it is required to provide the proper conditions for water filling prior to winding pre-compression.

The grouting protection of the reinforcement of the manufactured prestressed concrete pipes shall be done in accordance with the provisions of the applied technology.

Protection of cast concrete or mortar reinforcement shall be detailed in the design. It shall be performed only after tests have already been made to establish the construction details according to the specific conditions (distance between reinforcements, compaction ability, adherence to the support layer, etc).

The anti-corrosive protection systems of the grouted or laid layer surfaces shall be adopted and implemented in compliance with the provisions of the technical instructions C170-87 and part A of this practice guidelines.

The approval of expert institute or laboratory shall be asked for the cases that have not been detailed within the mentioned regulations.

Protection of anchorages

The steps below shall be implemented to protect the anchorages:

sufficient coverage with concrete;

high compaction of covering concrete;

previous laying of film;

other protections (casing and grouting, casing and lubrication).

9. QUALITY CONTROL AND COMMISSIONING OF PRESTRESSED CONCRETE WORKS

Implementation of prestressed works shall follow the requirements under the paragraph 1.7-1.11.

The quality of prestressed concrete works shall be ensured by:

Provision of a quality system by the respective manufacturer, according to the terms of SR EN ISO 9001-95 Quality systems. Pattern on insurance of production, mounting and service quality or at least,

Drawing and enforcement of a quality plan for the respective works, according to the requirements of the Regulation on constructions management and quality assurance.

The Constructor shall verify whether the design contains data required for checking of works quality.

Standing points shall be set, for which minutes on hidden works will be drawn out in respect to:

Construction of canals/ sheath and their status before grouting and inserting of sheath;

Construction of bundles, anchorages and their status;

Verification of control and friction force;

Laying of protections.

Moreover, the Constructor shall prepare question forms on control of works quality and he shall make sure this information is complete.

The Constructor and the Designer shall have direct and definite relations in order to implement corrective measures in case of discrepancies.

The Constructor shall provide the proper preliminary and construction conditions for pre-stressing operation.

Activities and numeric data under points 3.8a, 3.14, 3.20 and 3.24 shall be checked to control and certify the quality during manufacturing and installation of pre-elongated reinforcement, and data under points 3.37, 3.38 and 3.42 shall also be verified in case of post-elongated reinforcement.

Control and certification of quality on pre-stressing operation shall be done in accordance with the requirements of point 7.4, 7.6, 7.7, 7.8, 7.11 and 7.14 for pre-elongated reinforcement and points 7.4, 7.17, 7.21, 7.22, 7.23, 7.24, 7.29, 7.33 and 7.37 for the post-elongated reinforcement.

In case of special pre-compressing procedures (e.g winding), control and certification of quality shall be done in compliance with the regulations related to these procedures.

Control and certification of quality on post- elongated by cement mixture grouting operation shall be done in accordance with the requirements of point 8.7 and 8.20.

In case of grouting materials (plasticized tar, epoxy resins, basic rubber products) or of some special technologies (e.g vacuuming), control and certification shall follow the requirements of point 8.1.

Quality of outside prestressed concrete or cement reinforcement protection shall be controlled and verified in accordance with the requirements under part A of this practice guidelines and instructions C130-78.

Control and certification of quality on prestressed concrete elements and structures by loading tests shall be done in accordance with the technical specifications and related regulations (STAS 6657/1-89).

10. MEASURES ON LABOUR SAFETY AND FIRE PROTECTION

Implementation of prestressed concrete works shall observe the norms of labour protection on construction-mounting activities mentioned in Regulation on protection and hygiene of labour in constructions issued by Order of MLPAT no 9/1993 and the following specific requirements:

At the beginning of the pre-stressing works, the work agreement shall be prepared (acc. to NDPMCM);

During pretensioning process and transfer of prestressing force, measures will be taken so that workers shall neither enter nor stand behind the presses or along the technological lines; warning panels shall be installed.

In reference to the pre-elongated reinforcement elements, the ends of support or movable mould will be equipped with metallic guard (jointed to the support abutments or to the ends of mould) that raise in front of anchorages providing the needed protection);

In reference to the post-elongated reinforcement elements, special preventive measures shall be implemented during pretensioning operation so that the possible design of anchoring wedge, press, wires or bundles due to wires or bundle breaking, anchorage yielding, breaking of the tensioning installation, faulty handling, etc could not incur work accidents.

During pretensioning process, metallic sheath shall be mounted concentrically from the anchorage ring;

The personnel working at prestressed concrete works will be instructed to use properly the respective installations and on the following general issues:

Causes that might incur breaking of wires, sudden slippage from anchorages, violent reinforcement release from the press caused by material faults (concrete, wires, anchorages, pre-stressing installations) and faulty operation (non- calibration of anchorages on the canals gap, lack of timing in growing of pressure while tensioning on both ends of bundle, sudden decrease of pressure, hitting of anchorages after blocking, etc);

Possible directions of anchorages and pretensioned reinforcement, in case of yielding;

Danger of accidents entailed by the jet of fluid in the pressing and grouting installation when the working pressure is high, in case of joints yielding or installations damage;

Arrangement of working place so that the pretensioning team could work in the side position as against the reinforcement under tensioning process;

Fastening of presses not to fall in case of sudden release;

A frame shall be installed on the working support or boat floor to prevent falling of tools, anchorages, spare parts, etc stored on the respective platform;

The protection equipment proper of this type of works shall be worn (hamlet during the pre-stressing operations, protection glasses during grouting operations);

Release of press from the cranes hook during pre-stressing;

Working points and material storehouses shall have fire brigades supplied with sand boxes, shovels, slitters and portable chemical foam extinguishers.

In order to avoid electrocution accidents, the electric accidents shall be earthed. The electric resistance of the earthing installations shall be measured twice a year.

APPENDIX 1

REFERENCE DOCUMENTATIONS

APPENDIX 2

NOTIONS CHARACTERIZING PRESTRESSED CONCRETE

APPENDIX 3

DETAILS AND TECHNICAL REQUIREMENTS TO BE INCLUDED INTO THE CONSTRUCTION DESIGN AND TECHNICAL SPECIFICATIONS

Quality of steel used to manufacture prestressed and non-prestressed reinforcement and type of temporary protection laid in the manufacture, if needed, including the anchoring requirements.

Anchoring radii/ radiuses in the deviation points of the prestressed reinforcement, marking of tangent and change in curvature points.

Manner of ducts construction (coated or uncoated), tightness at jointing of sheaths and passing of canals through the joints between blocks or panels.

Points where the grouting and air release outlets are placed as well as their construction details.

Special measures shall be taken for the pre-elongated reinforcement in case the distances between reinforcements are less than the sizes in the pre-stressing technical procedure (reinforcement deviation, overlapping of anchorages, etc).

Location and their construction details of the devices that maintain the prestressed reinforcement in the correct position during concrete casting and vibration as well as maximum permitted tolerances from the project values.

Sequence for mounting of different elements of the reinforcement.

Concrete class, control transfer resistance and eventually applicable to other stages (removal of frames, handling, delivery, etc), the brand of grouted concrete, class of protection concrete.

Other parameters required to define the quality of concrete: tightness, frost-thaw resistance, wear resistance, possible special requirements regarding the cement types to be used or maximum sizes of aggregates, etc.

Requirements regarding the laying of concrete (sections where laying of concrete shall start from, laying direction, maximum thickness of layers, manner of compaction, possible laying joints), treatment of laid concrete after pouring.

The elements consisting of blocks or panels: shape and size of joints, manner of treatment of the contact surface in the joints, manner of propping of blocks and filling of joints, brand of mortar in joints as well as its minimum allowed resistance in the pre-compression time, details needed for construction, propping, monitoring.

In reference to the composite elements, treatment of the contact surfaces of the precast elements, propping way during manufacturing, etc.

Constructive measures that shall be taken so that the respective element could have the appropriate weight, at finalization of prestressing operations, to be functional.

Requirements on pretensioning of reinforcement:

Constructive measures to betaken to provide the design static plan for the pre-stressing phase;

Sequence of reinforcement pretensioning;

Size of control unit strain and elongation limits for each prestressed reinforcement;

Mention of bundles to be prestressed simultaneously;

In case of pre-stressing by phases, the concrete minimum strength, number of elongated reinforcement and control unit strain corresponding to each phase;

Size of technological stress losses considered at design; the pre-elongated reinforcement elements should show the technological loss of both construction alternatives, on movable and fix mould;

At pre-compression of the first constructive elements, the effective force-elongation diagram for the bundle, real stress losses because of frictions on alignment, the local strains and slips into anchoring are bound to by checked by direct measurements.

The Constructor, in agreement with the Designer, is bond to inform and set the measures to be taken during pre-stressing of post-elongated reinforcement, if the required elongations do not comply with the limits in the pre-stressing programme defined after checking and determinations were made on site.

The maximum time period between pre-stressing and performance of reinforcement protection and the condition that during construction and laying of the protection course of outdoor prestressed reinforcement, the element shall have a certain load, if needed.

Propping, lifting, handling during storage, hauling and mounting of pre-fabricated and pre-cast elements.

In case of elements placed in aggressive environment, special requirements that shall be provided during construction, protection of the elements surface in contact with the aggressive environment, mandatory requirements for its continuous maintenance in operation;

If some tests are planed, the loading diagrams and control values shall be defined in accordance with the concrete strength at the trials time, the reinforcement strain and stress losses in the prestressed reinforcement occurred until loading time;

Determined construction phases, mentioning the laying points.

Permissible limit requirements at construction regarding sizes of elements, position of reinforcement, size of joints, concrete covering (considering the possible surface treatments).

Checking appropriate conditions of quality and commissioning of the pre-cast elements.

Summery of calculations.

The technological and installation designers as well as for the constructions designer are bond to avoid drilling, blocks blasting or dowel fastening into the pre-compressed concrete elements.

Special measures on protection of labour.

REMARK:

The date under points 1-26 are not restrictive, the Designer must mention any additional data required to have proper construction, safety and regular operation.

APPENDIX 4

MAIN FEATURES OF INCERC PRE-STRESSING PROCEDURES WITH POST-TENSIONED REINFORCEMENT

REMARKS:

a) Within the limit of the maximum number of wires provided for the bundles it is possible to use only even numbers for the bundles of columns 4, 5, 6 and a multiple of 3 for column 7.

b) Diameter of canal shall be connected to the diameter of the whole in the distribution plate, with a gradient of approximately 2⁰. Such connection may be done using plate trumpets or pieces of an adequate shape, removable.

c) The values in brackets refer to plates and walls with widths up to 100 mm, inclusive.

d) These values can be reduced up to 10 mm in the case of precast elements.

e) The large size is perpendicular on the axle of the road.

f) It is recommended to adopt the first values allowing using of a wider range of tensioning installations.

g) The distances are variable in case the hole in the distribution plate is oriented in such a way as to allow location the bolt and the extension of its axle does not intersect the near cone-ring.

h) The values between the brackets refer to distribution plates common for all anchorages.

In the case of metallic bolt anchorages, the values are applicable for the case when the bolt is set parallel to the closest edge of the section. In the case the bolt is located perpendicular on the closest edge, the minimum distance prescribed shall be measured starting from the axle of the plate under the bolt, which is placed near the edge of the section.

When placing the anchorages on the lower part of the section it is necessary to take into account the type of support for the element and the sizes of the plant.

In special cases, when cross reinforcement of end areas and when the concrete compaction are made under more difficult conditions, the distances shall be increased (example: anchoring nervures from the prestressed concrete tanks).

i) These values are just a rough guide and shall be determined according to the type of plant used on the construction site.

APPENDIX 5

DEVICES MADE BY INCERC

For:

reinforcement and manufacturing and assemblage

grouting protection

APPENDIX 6

EXECUTION OF BUNDLES CANALS AS PER APPENDIX 4

Existing materials and plants existing in the country allow the execution of canals in the following versions:

1. Coated canals

1.1. Cover without crease executed by helical rolling, made cold rolled band: A-fm-MT-0.3x60 or 0.3x60-MT-b, as per STAS 9150-80 80/A2k-03, as per STAS 9485-80

Table 6.1

*) depending on the equipment of the manufacturing machine, it is possible to execute also other intermediary types.

1.2. Cover with helical crease made of cold rolled band 0.6x137-MT-b, as per STAS 9150-80 or A2K-03, as per STAS 9485 80.

Table 6.2

*) Types introduce din the production for the SPIRO machine (used for the works of CNE Cernavoda).

1.3. PVC pipe cover as per STAS 6675/2-92

The connection of pipes can be ensured using PVC sleeves or coupling. In both cases, soldering shall be made using PCD 13 adhesive.

Recommended pipes depending on the type of bundle are indicated in table 6.3.

Covers whose walls have width higher than the one indicate din the table:

Table 6.3

.4. Pipe made of polyethylene cover as per STAS 10617/2-84.

Recommended pipes depending on the type of bundle are specified in table 6.4.

Connection is made by end-to-end welding. After welding, it is necessary to check with a calibrated piece whether the material spew, formed on the inside of the pipe prevents the insertion of bundle.

The polyethylene may be rolled which allows you to avoid connections.

For easier technological conditions or based on experimental verifications, it is possible to use pipes whose walls are less wide, and preferably without any connections on the run.

It is not allowed to use pipes with widths higher than the one specified in the table.

Table 6.4

1.5 Cover made up of metallic pipes with thin walls.

The inside diameter of pipes must observe the minimum values indicated in appendix 3.

Site quality control and certification of various types of covers shall be made examining the delivery documents, sizes, integrity of transversal section and of the crease.

2. Uncoated canals

2.1. It is recommended that uncoated canals executed by extracting the pipes/covers should only be applicable in the case of precast elements; it is not recommended to apply this procedure in the case of cast-insitu constructions.

2.2. In order to execute covers by extraction, it is possible to use pipes (made of PVC type 4-STAS 6675/2-92, polyethylene pipes type 4-STAS 10617/2-84, or metallic pipes) or covers without crease, by unwinding these when the concrete has hardened. The length of canals that can be executed following this procedure is the following:

a) with PVC pipes or polyethylene:

-maximum length of 9 mm, for rectilinear or angular deviation -up to 5⁰, inclusively, routes;

-maximum length of 7 m, for curved routes with angular ranging from 5⁰ to 20⁰.

b) with metallic pipes;

- maximum length of 6 m, only for rectilinear routes or with very small deviations.

c) With covers without crests:

- maximum length 1218 m (provided the band is not spliced on the length of the cover).

2.3. For higher canal lengths, pipes may be extracted from both ends of the canal, and splicing parts should be provided to remain embedded in concrete.

2.4. PVC pipes are not recommended to be used when the environment temperature at extraction is below +5⁰C, as they turn fragile below such temperature.

2.5. In order to catch the pipes for extraction, these shall be provided with an extraction end manufactured as per fig. 6, mounted by pipe heating.

2.6. Prior to being introduced in forming, pipes shall be checked for cracking, indentation etc.

2.7. It is recommended that pipes should mounted in the design position after having mounted the whole regular reinforcement, as well as of one of the side walls of the forming.

2.8. In order to ensure the design layout, pipes shall be set in position using a concrete steel grills located with no more than 1.50 m spacing between each other and attached by welding points to the regular reinforcement of the member. Pipes shall not be attached by wires to these grills or to reinforcement that is not pre-tensioned.

2.9. as they are introduced in the forming, pipes shall be greased with vaseline, oil etc.

2.10. Pipes must exceed in length the forming end by minimum 45 cm, in the case of layouts with a deflection angle up to 5⁰ inclusively, and by minimum 80 cm, in the case of layouts with a deflection angle higher than 5⁰.

2.11. The optimum extraction time shall be established during the production of the first item, as it depends on a series of variables on a case to case basis (cement used, water-cement ratio, outside temperature, item length etc.).

If the waiting time before extraction is too short, this might cause deformation in the canal, and if it is too long, the force necessary for extraction will increase beyond the normal limits, and may even lead to pipe breaking. In average execution conditions, the optimum time for extraction is 1 ¾ 2 ¼ hours after concrete pouring. In order to avoid that cover gets blocked in concrete, the cover must be displaced either by short pats or by rotations.

2.12. Extraction should be made using manual means (cable hauler). The force should not give unitary efforts to the pipe higher than 10N/mm².

2.13. In case the angle between the extraction cable and the axle of the pipe exceeds 10⁰, the pipe shall be guided, at the areas where it exits the forming, using a roll supported on a framing trestle, at a distance of approximately 80 cm off the framing end.

2.14. After the extraction, pipes shall be cleaned and properly maintained.

2.15. Other methods for canal execution may also be used, as long as they have experimentally checked, such as using hoses maintained under pressure or reinforced on the inside.

Canal continuity may be checked at maximum 12 hours after pipe extraction so as to allow remedy of possible flaws.

Fig. 6.1 Extraction end

[picture]

LEGEND: 1- collar;

2- Ring Φ34 x Φ22 x 3;

3-Nut M20

4-Cone

5-Special nut

APPENDIX 7

EXECUTION AND ACCEPTANCE OF RING-CONE AND BOLT METALLIC ANCHORAGES

1. Technical requirements:

1.1. Shape and sizes of anchorage constituent elements, should comply with the provisions under fig. 7.1, 7.2, 7.3, 7.4, 7.5, 7.6.

1.2. The maximum deviation shall be those indicated in the layout drawings, and the unacceptable sizes shall be as per STAS 2300-88.

2. Rules for quality checking

2.1. Checking the quality of anchorages shall be made piece by piece, by quality checkers within the manufacturing company. Upon beneficiarys request, its delegate may attend the checking.

2.2. The quality of material is checked against the quality certificate issued by the manufacturing society and includes tests regarding its behavior in contact with corrosive agents.

2.3. Checking will be completed regarding>

a) Sizes and their compliance with the prescribed tolerances;

b) Profile shape and condition of the exterior surface of cones.

c) Lack of cracks or structural flaws, to which purpose non-destructive control methods shall be used, such as: ultrasounds, radiography, sample request (for rings) with a conic bolt pressed up to 90% of the normal tearing force of the bundle corresponding to the ring.

For cones, it is possible that checking is made visually (using the magnifying glass).

d) Brinell hardness (Hb) for rings, respectively Rockwell (HRC) for cones, checking hardness, shall be made as per STAS 493-91 and STAS 165-83, for each anchor element, separately. Hardness tests shall be made in at least 3 points distributed relatively uniformly on one of the smooth sides of the ring or cone.

The average of values read should be included within the limits prescribed in fig. 7.1 7.5, provided the extreme values should not be lower, respectively higher than 3% than the limits of the rage prescribed.

Hardness checking in every element of the anchorage, shall be completed and warranted by the plants executing the thermal treatment.

3. Delivery

Ring-cone metallic anchorages for any type of bundles shall be delivered in batches, packed in crates and protected against corrosion.

Each batch of anchorages shall be accompanied by a certificate confirming the compliance with all quality technical requirements.

All constituent parts of ring-cone metallic anchorages shall be marked in such a way as to identify the producer and the manufacturing batch.

RING

Ring OLC 45 (STAS 880-88) improved at 235 270 HB

[picture]

CONE

Material: 41 MoCr 11 (STAs 791-88)

Thermal treatment: air hardening and reversion at 57 64 HRC

[picture]

NOTE:

-Profile in detail C may be executed as screw thread or parallel circles;

-Pace p may be 2.25 mm or 2.5 mm;

-Average class as per STAS 2300-88;

-Deviation from rectilinear generator of the profile crest (det. C) max. 0.05 mm

-Ovalization accepted after treatment, 0.1 mm.

Fig. 7.1 Anchorage for bundle 12 Φ 5

RING

Ring OLC 45 (STAS 880-88) improved at 260 300 HB

[picture]

CONE

Material: 41 MoCr 11 (STAS 791-88)

Thermal treatment: air hardening and reversion at 57 64 HRC

[picture]

NOTE:

-Profile in detail C may be executed as screw thread or parallel circles;

-Pace p may be 2.25 mm or 2.5 mm;

-Average class as per STAS 2300-88;

-Deviation from rectilinear generator of the profile crest (det. C) max. 0.05 mm

-Ovalization accepted after treatment, 0.1 mm.

Fig. 7.1 Anchorage for bundle 24 Φ 7

RING

Ring OLC 45 (STAS 880-88) improved at 300 350 HB

[picture]

Fig. 7.4. Anchorage for bundle 48 Φ 7

CONE

Material: 18 MoCrNi 13 (STAS 791-88)

Thermal and chemical treatment (cyanidation), surface hardening 55 64 HRC

[picture]

Fig. 7.5 Anchorage for bundle 48 Φ 7

BOLT ANCHORAGE

Material: OL 60 (STAS 500/2 80)

Legend:

Piulita hexagonala -hexagon nut

Inalta M2 (STAS 4972-89), sudata de dorn, pe contur high M2 (STAS 4972-89), welded on the bolt, on its contour.

Dorn- bolt

Zona nesudata un-welded area

Placi rezemare- supporting plates

Brida de fixare temporara a sirmelor SBP temporary attachment flange of SBP wires

Surub M 12-20 SR ISO 4018: 1994-Screw M12-20, SR ISO 4018: 1994

Fascicul Bundle

NOTE:

- The attachment flange of SBP wires shall be assembled with M 12 20 screws (SRISO 4018/1994) on the bolt, but only as long as the bundle is stretched;

-M 12 screws shall be welded on the bolt on all sides, except the side indicated as un-welded area in the drawing;

- In case the number of wires in bundle is lower than the maximum one, the a quota shall be correlated accordingly.

Fig. 7.6.

[picture

(Fig. 7.6 continued)

APPENDIX 8

INDIVIDUAL BLOCKING WITH COLLAR AND BANKS FOR BRAID 7Φ4 mm

FOR PRE-ELONGATED

SET OF BACS

Material 18 mnCr-10 (STAS 791-88)

Thermal treatment: cyanidation or carbonitriding

[picture]

COLLAR

Material OLC 45 (STAS 880-88) improvement at 40 45 HRC

[picture]

NOTE:

Average class as per STAS 2300-88.

APPENDIX 9

PRE-TENSIONING INSTALLATIONS FOR PRE-ELONGATED REINFORCEMENT, DRAWN UP BY INCERC

APPENDIX 10

PRE-TENSIONING INSTALLATIONS FOR POST-ELONGATED REINFORCEMENT, DRAWN UP BY INCERC

*) Net weight is the weight of constituents simultaneously manipulated during the operations related to pre-stretching; recoil wedges, supporting parts etc. (manipulated separately) are not included in the net weight.

APPENDIX 11

DETERMINATION OF FRICTION COEFFICIENTS (k, ), THE ELASTICITY MODULUS (E) AND THE ELONGATION (Δl)

Case I. The prestressed concrete element also contains rectilinear bundles.

a) The linear friction coefficient (k) whose value is expressed per meter or rectilinear canal, is determined with the following equation:

(1)

ln- e-base logarithm

F1 and F2 forces at the extremities of the rectilinear bundle

L- length of the rectilinear canal

b) Friction coefficient in the curvaceous areas of the bundles is determined with the following equation:

(2) or (3)

(if the design specifies angular deviations)

k/ml- the value of the linear friction coefficient

length of the curved areas

curve radius

φ- angular deviations of the curved areas, measured in Radians

A single average value ( can be determined; the value can also measured for bundles with close angular deviations.

c) The elasticity modulus of the bundles on a rectilinear route

(4)

force in the active extremity of the bundle (in daN)

A- the surface of the bundle section (

L- length of the bundle (m), between the marking drawn at the active extremity, used to measure elongation, and the contact area between the fascicle and the press at the passive extremity.

elongation (cm)

The degree of precision of the measurements can be increased by deduction from of the elongations corresponding to areas outside of the bundle route proper, and replacement of L with the exclusive length of the bundle route. The elongations to be deducted from shall be calculated with an elasticity module E= 1.92 x10 daN/cm

d) The probable elongation of symmetrical bundles at the two extremities is established with the following equations:

- for rectilinear bundles

(5)

- for curved bundles

(6)

As the case may be, can be replaced by

e) In the case of curved, asymmetrical bundles, length X is initially determined by tests, complying with the following equation:

(7)

The probable elongations at the two extremities shall be:

(8)

(9)

Case 2- The element does not contain rectilinear bundles

Pairs of bundles with similar or close curves are selected, and friction measurements shall be performed on them.

From the equations:

(10)

(10)

it follows that:

(11)

(11)

PRETENSIONING FILE No _______ Date ___________

Company  Type of INCERC Press F= 1250 kN

Site  Bundle length betw. markings 27.10 m

Working point Stipulated elongation 173 mm

Element: G1  Maximum penetration or tendons 5 mm

into the anchorage

Concrete precompression Pressure - pretensioning 416 bar

resistance  - blocking 100 bar

Gliding (penetration) of tendons into the anchorage A B

- reference position after pressing of cone mm 123 130

- reference position after transfer mm 113 121

- Differences  10 9

- Shortening of tendons between the marking and the anchorage mm 5 5

- Entry of tendons into the anchorage mm 5 4

DETERMINATION OF JETTING MIXTURE CHARACTERISTICS

1. General conditions

1.1. Preliminary tests concerning determination of the properties of the mixture shall be performed at temperatures between 17 and 23C.

1.2. Mixture properties during jetting works shall be determined within the limits of the environmental temperature specified in items 3.3, 4.2 and 5.2 of appendix hereunder.

1.3. The following cements shall be used to prepare the jetting mixture:

- PI 32.5 and PI 42.5 cements as per SR 388-95 Portland Cement

- HI 32.5 (42.5) or SRI 32.5 (42.5)- as per SR 3011-95 Hydrotechnical cements and sulphate-resistant cements

Cement temperature shall not exceed +40C. Sand 01 mm can be used for canals with a diameter > 150 mm; the quantity must not exceed 30% of total cement weight.

Approved additives are recommended for used, in order to improve characteristics of the jetting mixture such as fluidity and sedimentation. Additives shall be used taking into consideration provisions in item 4.4, part A of the present practice code.

The jetting mixture shall not contain more than 750 mg of chlorides per litre; drinking water must be used for preparation of the mixture.

1.4. Calcium chloride is forbidden, as well as any other substances containing chloride and causing reinforcement corrosion.

2. Preparation of the jetting mixture

2.1. The mixture shall be prepared in a tank with a minimum net/ working capacity of 100 l, capable of mechanical mixing of the mortar with a rotation speed of at least 1,500 rotations per minute.

2.2. Cement shall be dosed in reference to weight.

2.3. In case additives are used, they shall be introduced into the mixer after the entire cement quantity has been introduced, after which mixing shall continue for a further 2-3 minutes, or in compliance with the specifications in the technical agreements of the additives.

2.4. Mixing is performed circa 5 minutes after introduction of all components, after which the operation shall be continued intermittently (10-minute break, 3-minute mixing), for as long as the mixture is kept inside the tank, but no longer than an hour.

2.5. From the mixer, the mixture shall pass through a sieve with 1-2 mm screens, into the tank of the jetting pump. .

2.6. The fluidity of each charge must be measured before it is introduced into the tank of the jetting pump.

2.7. The tank of the jetting pump should be equipped with a manual mixing device, or a mechanical mixing device with a small rotation speed (maximum 100 rotations/min); mixing is performed intermittently until the operation is finished.

3. Fluidity

3.1. Fluidity is determined by measuring flow speed of the jetting through the metallic funnel indicated in figure 13.1.

3.2. The funnel shall be verified with water and will be considered appropriate if the water flow time is 112/10 02/10; in case water flow time is longer or shorter, the inferior orifice shall be adjusted accordingly.

In order to determine water flow time and respectively the flow time of the jetting mixture, the funnel shall be completely filled.

3.3. The measurement temperature shall be the temperature of the working point.

4. Sedimentation

4.1. Sedimentation is determined by measurement of the water quantity that is separated from the jetting mixture from a graded glass cylinder of 500-ml net capacity. (STAS 4095-87 Capacity measurement glass containers. Graded cylinders).

In the case of jetting mixtures with expansive/ dilatation additives, the cylinder shall be filled up to the 400 ml mark and the readings shall be performed at various time intervals so that a dilatation diagram may be drawn out.

4.2. The cylinder is placed in away from vibration or shocks and it shall be filled up to the 500 ml mark, after which it is covered with a lid. The cylinder must be kept at a temperature between +12-+25C. In the case of expansive additives, the temperatures shall be that of the working point.

4.3. After at least 2 hours, but not before the mixture has acquired the appropriate consistence so that is does not flow/ it remains still even at a steep inclination of the cylinder (circa 30), the separated water quantity is measured as accurately as possible with a graded cylinder of 50-100 mm normal capacity.

The quantity of water separated via sedimentation must not exceed 10 ml, for a mixture with fluidity between 3525.

The water resulted from sedimentation must be absorbed in 24 hours.

5. Compression resistance

5.1. The compression resistance to compression is determined after 7 days, as per STAS 1275-88 Concrete tests. Tests on hardened concrete. Determination of mechanical resistances, on cubes with the 7.07 cm or 10 cm edges. When manufacturing the test cubes, the forms must be sealed, in order to prevent leaking of the jetting mixture.

5.2. The cubes used for determination of compression resistance shall be kept at temperatures between +17-+23C.

Figure 13.1. Reference funnel

Execution tolerance: 0.1 mm

The section containing the drainage orifice shall be executed by facing

APPENDIX 14

PREPARATION METHODS OF THE JETTING FORM

1. Jetting forms (appendix 14.1) are filled in during execution of the respective operation, when all measurement specified in appendix 13 must be performed in order to make sure that the jetting mixture has all the appropriate features (fluidity, sedimentation) in compliance with the practice code hereunder.

2. Columns 11 and 12 in the jetting file/form are only completed for a single canal out of the entire series/ group of canals jetted during the same shift and with the same composition of the jetting mixture. The other columns are completed for all the injected canals.

3. The Observation column 16 includes possible incidents occurring during jetting of the canal, such as: clogged canals interruption of jetting because of equipment malfunctions etc.

4. The jetting file/ form shall be filled in the appended file

JETTING FORM No_________________