Construction rules

6.3.1 Concrete

P(1) The concrete used in construction shall be such that its specified properties will be maintained over the life of the structure.

(2) For the construction rules related to concrete and concrete technology, the relevant Sections in ENV 206 apply.

6.3.2 Formwork and falsework 6.3.2.1 Basic requirements

P(1) Formwork and falsework shall be designed and constructed so that they are capable of resisting all actions which may occur during the construction process. They shall remain undisturbed until the concrete has achieved sufficient strength to withstand the stresses to which it will be subjected on stripping or release, with an acceptable margin of safety.

P(2) The formwork and falsework shall be sufficiently stiff to ensure that the tolerances for the structure are satisfied and that its loadbearing capacity is not affected.

P(3) The general lay-out of the formwork shall be such that the correct placing of reinforcement and tendons as well as correct compaction of the concrete is possible.

P(4) The formwork and the falsework shall be designed and erected (in accordance with national standards) by suitably trained persons. Supervision and control shall be such as to ensure that the erection is completed in accordance with the drawings and specifications.

P(5) The formwork shall be capable of being removed from the concrete without causing shock or damage.

(6) Where necessary, the camber built into the formwork should be that required by the designer of the structure and falsework.

(7) Ground support for the falsework should also be constructed by suitably trained personnel in accordance with the drawings and specifications. Deformations and displacements imposed by prestressing should be taken into account in the design of the falsework.

(8) Joints between the panels of the formwork should be adequately tight.

(9) The internal surface of the formwork must be clean. Approved mould-release agents should be applied in continuous and uniform layers on the internal surface and the concrete should then be placed while these agents are still effective. Any possible detrimental influence of these agents on the concrete surface has to be taken into consideration.

(10) Formwork spacers left in the concrete should not impair its durability or appearance

6.3.2.2 Surface finish

P(1) The formwork shall be designed and constructed so that there is no loss of fines, or blemish of the concrete surface.

P(2) Where a particular grade or type of finish is required for practical or aesthetic reasons, the requirements shall be specified directly or by reference to appropriate national or international documents or by sample surfaces.

6.3.2.3 Temporary works inserts

P(1) Temporary works inserts may be necessary to assist in maintaining formwork, or bar reinforcement or ducts or other similar items, in place until the concrete has hardened.

P(2) Such inserts shall not introduce unacceptable loading on the structure, shall not react harmfully with the constituents of the concrete or reinforcement or prestressing steel, and shall not produce unacceptable surface blemishes.

(3) The use of light alloy inserts (aluminium etc) is prohibited.

6.3.2.4 Removal of formwork and falsework

P(1) The time at which formwork and falsework is removed shall be determined by consideration of the following criteria:

a) The stresses that will be induced in the concrete when the formwork/falsework has been removed;

b) The concrete strength at the time of removal;

c) The ambient climatic conditions and the measures available to protect the concrete once the formwork is removed;

d) The presence of re-entrant angle formwork, which should be removed as soon as possible, while complying with other removal criteria.

(2) General information on curing and on striking formwork is given in 10.6, 10.7 and 10.8 of ENV 206.

(3) The time between casting and removal of the formwork depends mainly on the strength development of the concrete (see ENV 206, Table 13) and on the function of the formwork. In the absence of more accurate data, the following minimum periods are recommended:

| _2 | days for non-load bearing parts of formwork (e.g. vertical formwork of beams; formwork for columns and walls); | _5 | days for the formwork of slabs cast in situ;

| 10 | days for direct load-bearing formwork, e.g. soffits of beams or slabs. Where sliding or climbing formwork is used, shorter periods than recommended above may be permitted. 6.3.3 Reinforcing steel

6.3.3.1 Basic requirements

P(1) Reinforcing steel shall comply with the requirements of 3.2 of this Code, with relevant Euronorms or, where these do not exist, with CEN, ISO, or national standards, or shall be approved by the National Building Regulations Control Authority.

(2) Only steel specified in the design documents may be used as reinforcement.

6.3.3.2 Transport, storage and fabrication of the reinforcement

P(1) Steel reinforcing bars, welded mesh reinforcement and prefabricated reinforcement cages shall be transported, stored, bent and placed in position so that they do not suffer any damage.

P(2) The surface condition of the reinforcement shall be examined prior to use, to ensure that it is free from deleterious substances which may adversely affect the steel or concrete or the bond between them.

P(3) Reinforcing steel shall be cut and bent in accordance with appropriate international or national standards.

(4) The following should be avoided:

— Rupture of welds in prefabricated reinforcement cages and in welded fabrics;

— Surface deposits damaging bond properties;

— Lack of identification of reinforcement;

— Reduction of the section through corrosion, beyond certain permissible limiting values.

6.3.3.3 Welding

P(1) Welding must only be carried out on reinforcing steel that is suitable for welding.

P(2) Welded connections must be made and checked by persons suitably trained in welding of reinforcement.

P(3) Welding shall be performed in accordance with international or national standards.

P(4) Where a risk of fatigue exists, the welding of reinforcement must conform to special requirements as given in relevant standards.

P(5) The production and checking of the welded connections shall comply with the relevant requirements in international or national standards. (6) Welding methods permitted include:

— electric flash welding;

— electric resistance welding;

— electric arc welding (with coated electrodes or under a protective gas envelope);

— high pressure gas welding.

6.3.3.4 Joints

P(1) The length and position of lapped joints shall be in accordance with the design and the drawings. If the bar lengths delivered to the site do not conform with the drawings, then modifications shall only be introduced with the approval of the designer or of the supervisory authority.

P(2) In general, reinforcing bars shall not be welded at or near bends in a bar.

(3) Joints made with mechanical connecting devices should be carried out in accordance with

Clause 5.2.3.5 of this Code and with the specified Standards or Approval documents.

6.3.3.5 Fabrication, assembly and placing of the reinforcement

P(1) The assembly of the reinforcement shall be robust enough to ensure that the bars do not shift from their prescribed position during transportation, placing and concreting. The specified cover to the reinforcement shall be maintained by the use of approved chairs and spacers.

P(2) The tolerances required for the fixing of reinforcement shall be as given in 6.2. Alternatively, they shall be stated in the contract documents.

P(3) Bending should be carried out by mechanical methods, at constant speed without jerking, with the aid of mandrels so that the bent part has a constant curvature. If the ambient temperature is lower than a specified value, additional precautions may be needed.

P(4) The reinforcement shall be secured against any displacement and the position of the reinforcement shall be checked before concreting.

P(5) In areas of congested reinforcement, sufficient spacing of the bars shall be provided to allow proper compaction of the concrete.

6.3.4 Prestressing steel

6.3.4.1 Basic requirements

P(1) Prestressing steel shall comply with the requirements of 3.3 of this Code, the relevant Euronorms, or where these do not exist, with CEN, ISO or national standards, or shall be approved by the National Building Regulations Control Authority.

P(2) The prestressing devices (anchorages, couplers, sheaths and ducts) shall comply with the requirements of 3.4 of this Code, the relevant Euronorms, or where these do not exist, with CEN, ISO or national standards, or shall be approved by the National Building Regulations Control Authority.

(3) The tendons, (wire, bars, cables), anchorage devices, couplers and sheaths used shall be those in the project design documents. They shall be capable of being identified as such.

6.3.4.2 Transport and storage of the tendons

P(1) Tendons, sheaths, anchorage devices and couplers shall be protected from harmful influences during transport and storage and also when placed in the structure, until after concreting has taken place.

(2) During transport and storage of the tendons, the following should be avoided:

— any type of chemical, electro-chemical or biological attack liable to cause corrosion;

— any damage to the tendons;

— any contamination liable to affect the durability or bond properties of the tendons;

— any deformation of the tendons, not provided for in the design;

— any unprotected storage, exposure to main or contact with the ground;

— the use of water transport without suitable packaging;

— welding in the vicinity of prestressing tendons without the provision of special protection (from splashes).

(3) For the sheaths, the following should be taken into consideration:

— local damage and corrosion inside should be avoided;

— water-tightness should be ensured;

— it should be resistant to mechanical and chemical attack.

6.3.4.3 Fabrication of tendons

P(1) The devices used in jointing the tendons, for their anchorage and coupling shall be as specified in standards or Approval Documents. The prestressing members shall be assembled and placed in position in accordance with the standards or Approval documents. The sheaths and their connections shall be as specified in the project design documents.

(2) Particular consideration should be given to

— maintaining the identification marks on all materials;

— the appropriate methods for cutting;

— the straight entry into the anchorage and couplers as required by the manufacturer;

— transportation; when lifting by crane, any local crushing or bending of the tendons should be avoided.

6.3.4.4 Placing of the tendons

P(1) Placing of the tendons shall be carried out in compliance with the criteria relating to:

— the concrete cover and the spacing of the tendons;

— the permissible tolerances in respect of the position of the tendons, couplers and anchorages;

— the ease with which the concrete can be cast.

P(2) The tolerances required for the placing of the prestressing tendons shall be those given in 6.2. Alternatively they shall be stated in the contract documents.

(3) The sheaths should be fixed carefully according to the designer's specification of dimensions, spacers and supports.

(4) After placing the sheaths in position, vents should be provided at both ends and at their high points, as well as at all points where air or water may accumulate; in the case of sheaths of considerable length, vents are also needed at intermediate positions.

(5) The sheaths should be protected from penetration of extraneous materials until the completion of grouting.

6.3.4.5 Tensioning of the tendons

P(1) Prestressing shall be in accordance with a pre-arranged stressing programme.

P(2) Written instructions shall be provided at the site or in the factories or plants on the prestressing procedure to be followed.

P(3) Workmen and staff engaged in stressing shall be skilled and have had special training.

P(4) During prestressing, suitable safety measures should be taken and be recorded by an engineer.

6.3.4.5.1 Pre-tensioning

(1) In the case of pre-tensioning the instructions for prestressing shall specify:

— the prestressing tendons and the prestressing devices;

— any special sequence in which the prestressing tendons are to be tensioned;

— the jack pressure or the forces at the jacks which must not be exceeded;

— the final pressure which must be attained after stressing has been completed or the corresponding forces at the jack;

— the maximum permissible extension of the tendons and slip in the anchorages;

— the manner and sequence in which the tendons are to be released;

— the required concrete strength at the time of release, which should be checked;

— operational suitability of re-useable anchorage components.

(2) The necessity for a temporary protection of the tendons after tensioning and before casting should be checked. Where necessary, the protective material should not affect bond and should have no detrimental effect on the steel or the concrete.

6.3.4.5.2 Post-tensioning (1) The following shall be a) Specified by the designer:

— the prestressing process to be employed;

— the type and grade of the prestressing steel;

— the number of bars or wires in the individual tendons;

— the required concrete strength prior to tensioning;

— the order in which successive tendons should be tensioned, specifying the location where the tension is to be applied;

— where appropriate, the time of the removal of the falsework during tensioning;

— the force required to be developed at the jack;

— the design elongation required;

— the number, type and location of couplers.

b) recorded by the supervising engineer during the tensioning process:

— the type of prestressing devices used which should be calibrated;

— the elongation measured on site;

— the measured pressure in the jacks;

— the observed value of slip;

— the deviation of the measured values from the design values.

— the actual concrete strength;

— the actual order in which successive tendons are tensioned;

— where appropriate, the time at which the formwork has been removed. 6.3.4.6 Grouting and other protective measures

6.3.4.6.1 General

P(1) Tendons placed in sheaths or ducts in the concrete, couplers and anchorage devices shall be protected against corrosion.

P(2) Should the delay between stressing and grouting exceed the time permitted, then protection of the tendons shall continue until grouting takes place.

P(3) Where temporary protection is provided, the material used shall have an approval document and shall not have a deleterious effect on the prestressing steel or on the cement grout.

P(4) Written instructions shall be provided for the site or the works for the preparation and execution of the grouting.

P(5) If frost is liable to occur, measures shall be taken to prevent freezing of water in sheaths which are not yet grouted. After a period of frost, the sheaths should be free from ice before grouting is started.

(6) Corrosion protection of the tendons is ensured by filling all voids with a suitable grouting material (usually cement mortar); as a rule, the anchorage should be enveloped in concrete or mortar.

The above objective is met by:

— using approved grout materials (must remain alkaline, no harmful components) and by covering the tendons completely:

— filling the ducts completely (including voids between tendons) with a grout which after hardening fulfils the structural requirements (strength, bond, modulus of elasticity, shrinkage).

6.3.4.6.2 Cement grout

P(1) The cement grout used shall have adequate properties e.g.

— high fluidity and cohesion when plastic;

— low shrinkage deformation when hardening;

— adequate strength and resistance to freezing when hard;

P(2) Appropriate materials (type of cement, admixtures) shall be used and the mixing process (batching, w/c-ratio, procedure, time) shall ensure the required properties.

P(3) Chlorides (as % by mass of cement) from all sources shall not exceed the values given in the national standards.

P(4) For the types of cements used for grouting, see EN... (yet to be drafted)

6.3.4.6.3 Instructions to the site

P(1) Before grouting starts, the following preconditions shall be fulfilled:

— operational equipment (including "stand by" grout pump to avoid interruptions in the event of malfunction);

— permanent supplies of water under pressure and of compressed air;

— materials batched (excess to allow for overflow);

— ducts free of harmful material (e.g. water, ice);

— vents prepared and identified;

— preparation of control tests for grout;

— in case of doubt, grouting trial on representative ducts;

— grout flow not affected.

P(2) The grouting programme shall specify

— the characteristics of the equipment and of the grout;

— order of blowing and washing operations;

— order of grouting operations and fresh grout tests (fluidity, segregation);

— grout volume to be prepared for each stage of injection;

— precautions to keep ducts clear;

— instructions in the event of incidents and harmful climatic conditions;

— where necessary, additional grouting.

6.3.4.6.4 Grouting operations

(1) Before injecting, it should be checked that the grouting programme can be fulfilled.

(2) The injecting process should be carried out at a continuous and steady rate. In some circumstances (large diameter, vertical or inclined ducts) post-injection may be necessary to replace bleed water by grout.

(3) After completion of grouting, loss of grout from the duct should be prevented. To allow expansion of grout during hardening and to displace bleed water, appropriate vents may be opened.

(4) After injecting, if large voids are suspected, the effectiveness of grouting should be checked with appropriate equipment.

6.3.4.6.5 Sealing

P(1) Where necessary, all openings, grouting tubes and vents shall be sealed hermetically to prevent pentration of water and harmful products (e.g. anti-freeze or de-icing agents).

6.3.4.6.6 Other protections

(1) Tendons may be protected by materials based on bitumen, epoxy resins, rubber, etc, provided that there are no detrimental effects on bond, fire resistance, and other essential properties.

Greener Homes for You

Greener Homes for You

Get All The Support And Guidance You Need To Be A Success At Living Green. This Book Is One Of The Most Valuable Resources In The World When It Comes To Great Tips on Buying, Designing and Building an Eco-friendly Home.

Get My Free Ebook


Post a comment