EP0078564A2 - Prestressing strand for concrete structures and concrete structures containing such strand - Google Patents
Prestressing strand for concrete structures and concrete structures containing such strand Download PDFInfo
- Publication number
- EP0078564A2 EP0078564A2 EP82201303A EP82201303A EP0078564A2 EP 0078564 A2 EP0078564 A2 EP 0078564A2 EP 82201303 A EP82201303 A EP 82201303A EP 82201303 A EP82201303 A EP 82201303A EP 0078564 A2 EP0078564 A2 EP 0078564A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- treatment
- outer wires
- core wire
- wire
- strand
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Images
Classifications
-
- D—TEXTILES; PAPER
- D07—ROPES; CABLES OTHER THAN ELECTRIC
- D07B—ROPES OR CABLES IN GENERAL
- D07B1/00—Constructional features of ropes or cables
- D07B1/06—Ropes or cables built-up from metal wires, e.g. of section wires around a hemp core
- D07B1/0693—Ropes or cables built-up from metal wires, e.g. of section wires around a hemp core having a strand configuration
-
- D—TEXTILES; PAPER
- D07—ROPES; CABLES OTHER THAN ELECTRIC
- D07B—ROPES OR CABLES IN GENERAL
- D07B5/00—Making ropes or cables from special materials or of particular form
- D07B5/005—Making ropes or cables from special materials or of particular form characterised by their outer shape or surface properties
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
- E04C5/08—Members specially adapted to be used in prestressed constructions
-
- D—TEXTILES; PAPER
- D07—ROPES; CABLES OTHER THAN ELECTRIC
- D07B—ROPES OR CABLES IN GENERAL
- D07B2201/00—Ropes or cables
- D07B2201/20—Rope or cable components
- D07B2201/2047—Cores
- D07B2201/2052—Cores characterised by their structure
- D07B2201/2059—Cores characterised by their structure comprising wires
-
- D—TEXTILES; PAPER
- D07—ROPES; CABLES OTHER THAN ELECTRIC
- D07B—ROPES OR CABLES IN GENERAL
- D07B2201/00—Ropes or cables
- D07B2201/20—Rope or cable components
- D07B2201/2047—Cores
- D07B2201/2052—Cores characterised by their structure
- D07B2201/2065—Cores characterised by their structure comprising a coating
-
- D—TEXTILES; PAPER
- D07—ROPES; CABLES OTHER THAN ELECTRIC
- D07B—ROPES OR CABLES IN GENERAL
- D07B2401/00—Aspects related to the problem to be solved or advantage
- D07B2401/20—Aspects related to the problem to be solved or advantage related to ropes or cables
- D07B2401/205—Avoiding relative movement of components
-
- D—TEXTILES; PAPER
- D07—ROPES; CABLES OTHER THAN ELECTRIC
- D07B—ROPES OR CABLES IN GENERAL
- D07B2501/00—Application field
- D07B2501/20—Application field related to ropes or cables
- D07B2501/2015—Construction industries
- D07B2501/2023—Concrete enforcements
Definitions
- the invention relates to prestressing strand for use in a concrete structure, comprising at least one central core wire and a plurality of outer wires extending helically along the core wire to envelop it.
- Such strands are often used as the tensioned reinforcing elements in prestressed concrete structures, in which they may for example be inserted in curved conduits in the concrete structure.
- the conduits are formed for example by tubes of steel or another material, which are pre-cast into the concrete structure.
- the invention also relates to a process of manufacturing such strand and to a concrete structure containing such strand.
- a commonly used type of prestressing strand comprises six equally thick outer wires and one single core wire the diameter of which is between 2 and 5 percent greater than that of the outer wires. This larger size of the. core wire is of importance in obtaining a strand which has good coherence and in which the outer wires fit tightly against the core wire.
- this type of strand form is the most popular one used for prestressing, the invention is 4 not restricted to this specific strand construction, but also relates to other strand constructions of the general type indicated in the first paragraph above.
- Figs. 1 and 2 of the accompanying drawings show a prestressing strand having a single core wire b and six outer wires a in longitudinal view and in cross section respectively.
- Fig. 1 also indicates the pitch of the helices in which each of the outer wires lies. For the whole strand, this pitch S is referred to herein by the expression "helical pitch length”.
- Fig. 2 indicates the greatest cross sectional dimension which is herein called the maximum diameter of the strand. It is usual to express the helical pitch length as a multiple of the strand diameter. For prestressing strands, this length S generally lies between 12 and 18 times the diameter, although a value of S in this range is not essential for the present invention.
- the present invention arises because, for prestressing strand, investigations do not appear to have resulted in the most suitable practical strand construction for use in prestressing.
- the modulus of deformation in cases of substantial variation is as a rule smaller than the modulus of elasticity. This is the more serious, because in the application of a calculated elongation to the prestressing strand, an uncertainty exists whether along the whole length, the designed tension exists in the strand, and whether the concrete structure arrives at the desired condition of prestress.
- the tension condition and the deformation condition of a prestressing strand in a curved configuration, in which the strand is subjected to transverse forces and frictional forces, is highly complex, and is dependent on a great number of factors which are related to the properties of the material and the production methods for the strand.
- the object of the present invention is therefore to make it possible to control and minimize variations in tension in prestressing strand in curved conduits.
- the inventors have realised that a considerably better consistency between the modulus of deformation and the modulus of elasticity can be obtained when the core wire can be more adequately tensioned over its whole length and can cooperate better as a load bearing element. Also the prestressing strand must sufficiently remain integral in order that slip between the core wire and the outer wires is prevented, since this slip has the result that locally the core wire is no longer fully under load.
- the outer wires may also have a modified surface resulting in a reduced tendency to such movement.
- the core wire, and optionally also the outer wires have been subjected to a treatment to modify the wire surface so that the resistance to relative longitudinal movement of the core wire and the outer wire is greater than it would be if the treatment had not been performed.
- One treatment method for the core, and optionally the outer wires is to form mechanically indentations in the wire surface.
- Another treatment method is to modify the surface condition of the wire so as to increase the coefficient of friction between the core wire and the outer wires.
- This frictional properties instead of accepting undesired variations in the frictional properties inside the strand, use is made of these frictional properties, by increasing this friction in order to reduce or even prevent any movement in longitudinal direction between the core wire and the outer wires.
- the surface condition of the wire can be adequately modified by subjecting it to a chemical etching treatment.
- Chemical etching treatments of steel products are generally known, which means that no further explanation needs to be given how such etching is to be performed in order to achieve a slight roughening of the surface, without unduly affecting the physical properties of the material.
- the object of the present invention may be obtained, without modifying the wire itself, if a resin coating in which an abrasive powder, e.g. a grinding powder such as carborundum, is admixed is applied to the wire.
- an abrasive powder e.g. a grinding powder such as carborundum
- the particles of the grinding powder prevent or at least reduce movement between the various wires.
- wire treatment consists in depositing a friction-increasing substance upon the wire by an electrochemical or an electrostatic process.
- electrochemical or an electrostatic process there are many options available to the expert for achieving suitable deposition.
- the invention also relates to the process of manufacture of the prestressing strand and to a concrete structure containing one or more tensioned strands according to the invention, as described above.
- the manufacturing steps start from wire of surface condition hitherto conventional in this field, e.g. as supplied by wire manufacturers.
- Figs. 3 and 4 show a concrete plate 1 with a thickness of 22 cm. Through this plate 1 there extends a conduit 3 which over an angle of 5.07 radians is curved with a radius of curvature R of 100 cm. The length L 2 of the curved conduit part is consequently 507 cm. Across each end of the conduit 3 there is located a support beam 2 with at the left hand side a wedge anchoring 5 for a prestressing strand and at the right hand side a similar wedge anchoring 5 behind a hydraulic press 4 (schematically shown).
- the tensioned strand then consists of a straight section of length L 1 of 175 cm, a curved section of length L 2 of 507 cm and another straight section of length L 3 of 210 cm.
- Tests were carried out using the most common prestressing strand of thickness D of 0.5 inches, and having a core wire and six outer wires.
- the strand was brought under nominal tension, in order to stretch it sufficiently, whereupon the tension force was increased up to a value near the usual full load value used in tensioning technology. During the increase of the tension force, the elongation and the tension force in the strand were measured continuously.
- the strand was considered to be divided into elements, and for each element the stress and strain conditions were calculated with the application of a frictional force between the channel wall and the prestressing strand.
- frictional coefficients between the strand and the channel wall at various tension forces in the strand were determined. Per element, these friction coefficients were introduced into the calculation so that it was possible to determine by calculation, what tension forces should be present in the strand, on the basis of the total measured extension of the strand between the anchors 5. This value was compared with the actual tension forces obtained, from which a value could be obtained for the modulus of deformation in each test performed.
Landscapes
- Engineering & Computer Science (AREA)
- Architecture (AREA)
- Civil Engineering (AREA)
- Structural Engineering (AREA)
- Ropes Or Cables (AREA)
- Reinforcement Elements For Buildings (AREA)
- Reinforced Plastic Materials (AREA)
- Investigation Of Foundation Soil And Reinforcement Of Foundation Soil By Compacting Or Drainage (AREA)
- Paper (AREA)
- Rod-Shaped Construction Members (AREA)
- Curing Cements, Concrete, And Artificial Stone (AREA)
Abstract
Description
- The invention relates to prestressing strand for use in a concrete structure, comprising at least one central core wire and a plurality of outer wires extending helically along the core wire to envelop it. Such strands are often used as the tensioned reinforcing elements in prestressed concrete structures, in which they may for example be inserted in curved conduits in the concrete structure. The conduits are formed for example by tubes of steel or another material, which are pre-cast into the concrete structure. The invention also relates to a process of manufacturing such strand and to a concrete structure containing such strand.
- A commonly used type of prestressing strand comprises six equally thick outer wires and one single core wire the diameter of which is between 2 and 5 percent greater than that of the outer wires. This larger size of the. core wire is of importance in obtaining a strand which has good coherence and in which the outer wires fit tightly against the core wire. Although this type of strand form is the most popular one used for prestressing, the invention is 4 not restricted to this specific strand construction, but also relates to other strand constructions of the general type indicated in the first paragraph above.
- Referring now to Figs. 1 and 2 of the accompanying drawings, these show a prestressing strand having a single core wire b and six outer wires a in longitudinal view and in cross section respectively. Fig. 1 also indicates the pitch of the helices in which each of the outer wires lies. For the whole strand, this pitch S is referred to herein by the expression "helical pitch length". Fig. 2 indicates the greatest cross sectional dimension which is herein called the maximum diameter of the strand. It is usual to express the helical pitch length as a multiple of the strand diameter. For prestressing strands, this length S generally lies between 12 and 18 times the diameter, although a value of S in this range is not essential for the present invention.
- The present invention arises because, for prestressing strand, investigations do not appear to have resulted in the most suitable practical strand construction for use in prestressing.
- In the tensioning of a prestressing strand, usually the elongation properties of the strand under tensioning in an unhindered straight condition are employed. In this it has been found that the ratio between the mean stress over the cross section of the strand and its strain deviates little from the elasticity modulus E (Young's modulus) of the wire material. Small deviations can arise, in dependence on the production method of the strand and its construction.
- In the use of prestressing strands in curved conduits through concrete structures, in different cases different tension forces appear at the strand ends after tensioning. By means of calculations it is possible to find a relationship between the total elongation of the strand in the curved channel and these tension forces at the ends, from which it is then possible to learn about the behaviour of the tension forces in the strand along its length, by applying a predetermined elongation to the strand.
- It has now been found that in such cases, as a consequence of variations in the frictional properties inside the strand, variations in the production methods of the cable and possibly other factors, great deviations can be found between the calculated elongations and elongations actually occurring in the tensioning of prestressing strand. If the quotient of the mean stress over the strand cross section and the measured elongation of the strand per'unit length is referred to by the expression "modulus of deformation", then it is found that, when tensioning strand in curved conduits, this deformation modulus as a rule deviates considerably and unpredictably from the modulus of elasticity E of the wire material. More specifically it is found that the modulus of deformation in cases of substantial variation is as a rule smaller than the modulus of elasticity. This is the more serious, because in the application of a calculated elongation to the prestressing strand, an uncertainty exists whether along the whole length, the designed tension exists in the strand, and whether the concrete structure arrives at the desired condition of prestress.
- The tension condition and the deformation condition of a prestressing strand in a curved configuration, in which the strand is subjected to transverse forces and frictional forces, is highly complex, and is dependent on a great number of factors which are related to the properties of the material and the production methods for the strand.
- A complete understanding of this has not yet been achieved, though by an empirical method the inventors of the present application can indicate systematic variations. The method of testing strands is described.below.
- The object of the present invention is therefore to make it possible to control and minimize variations in tension in prestressing strand in curved conduits.
- The inventors have realised that a considerably better consistency between the modulus of deformation and the modulus of elasticity can be obtained when the core wire can be more adequately tensioned over its whole length and can cooperate better as a load bearing element. Also the prestressing strand must sufficiently remain integral in order that slip between the core wire and the outer wires is prevented, since this slip has the result that locally the core wire is no longer fully under load.
- It has been found that such improved prestressing strands of the above referred to type can be obtained if at least the or each core wire has a modified surface resulting in a reduced tendency to movement (e.g. increased coefficient of friction) of the core and outer wires relative to each other.
- The outer wires may also have a modified surface resulting in a reduced tendency to such movement. Thus the core wire, and optionally also the outer wires, have been subjected to a treatment to modify the wire surface so that the resistance to relative longitudinal movement of the core wire and the outer wire is greater than it would be if the treatment had not been performed. ,
- One treatment method for the core, and optionally the outer wires is to form mechanically indentations in the wire surface.
- Another treatment method is to modify the surface condition of the wire so as to increase the coefficient of friction between the core wire and the outer wires. Thus, instead of accepting undesired variations in the frictional properties inside the strand, use is made of these frictional properties, by increasing this friction in order to reduce or even prevent any movement in longitudinal direction between the core wire and the outer wires.
- Various alternative methods are available for modifying the surface condition of the core and outer wires in order to increase the coefficient of friction. One possibility is that the surface of the wire is given a thin oxide layer resulting from heating the wire in an oxidising atmosphere. It will be clear that even a very thin oxide layer can drastically influence the frictional properties of the wires, without affecting the strength and durability of the wire and of the prestressing strand as a whole. Anyone skilled in the art will know how for each type of core wire such a thin oxide layer can be achieved by selection of oxidising atmosphere, process temperature and a period of treatment of the wires, without affecting the relevant physical properties of the wire material, such properties being for example (but not exclusively) the mechanical properties and the durability.
- It has also been found that the surface condition of the wire can be adequately modified by subjecting it to a chemical etching treatment. Chemical etching treatments of steel products are generally known, which means that no further explanation needs to be given how such etching is to be performed in order to achieve a slight roughening of the surface, without unduly affecting the physical properties of the material.
- Also, it has been found that the object of the present invention may be obtained, without modifying the wire itself, if a resin coating in which an abrasive powder, e.g. a grinding powder such as carborundum, is admixed is applied to the wire. In prestressing strand constructed with such a coated wire, the particles of the grinding powder prevent or at least reduce movement between the various wires.
- Yet another possibility for the wire treatment consists in depositing a friction-increasing substance upon the wire by an electrochemical or an electrostatic process. In this field there are many options available to the expert for achieving suitable deposition.
- Although several different alternatives have been discussed for modifying the surface of the wire, combinations of two or more of such surface modification processes can be employed in the present invention.
- The invention also relates to the process of manufacture of the prestressing strand and to a concrete structure containing one or more tensioned strands according to the invention, as described above. In such a manufacturing process, it is assumed that the manufacturing steps start from wire of surface condition hitherto conventional in this field, e.g. as supplied by wire manufacturers.
- Embodiments of the invention will be described below by way of non limitative example with reference to the accompanying drawings, in which:
- Figs. 1 and 2 show a prestressing strand and have been described above;
- Fig. 3 shows a test apparatus for prestressing strand in plan view;
- Fig. 4 is a front view of the apparatus of Fig. 3;
- Figs. 3 and 4 show a concrete plate 1 with a thickness of 22 cm. Through this plate 1 there extends a
conduit 3 which over an angle of 5.07 radians is curved with a radius of curvature R of 100 cm. The length L2 of the curved conduit part is consequently 507 cm. Against each end of theconduit 3 there is located asupport beam 2 with at the left hand side a wedge anchoring 5 for a prestressing strand and at the right hand side a similar wedge anchoring 5 behind a hydraulic press 4 (schematically shown). - After a strand is inserted through the
conduit 3, the strand is secured by the wedge anchors 5, whereupon it is tensioned by the hydraulic -press 4. The tensioned strand then consists of a straight section of length L1 of 175 cm, a curved section of length L2 of 507 cm and another straight section of length L 3 of 210 cm. - Tests were carried out using the most common prestressing strand of thickness D of 0.5 inches, and having a core wire and six outer wires. First the strand was brought under nominal tension, in order to stretch it sufficiently, whereupon the tension force was increased up to a value near the usual full load value used in tensioning technology. During the increase of the tension force, the elongation and the tension force in the strand were measured continuously.
- Using the "element method", the strand was considered to be divided into elements, and for each element the stress and strain conditions were calculated with the application of a frictional force between the channel wall and the prestressing strand. By means of separate tests with small angles of wrap, frictional coefficients between the strand and the channel wall at various tension forces in the strand were determined. Per element, these friction coefficients were introduced into the calculation so that it was possible to determine by calculation, what tension forces should be present in the strand, on the basis of the total measured extension of the strand between the anchors 5. This value was compared with the actual tension forces obtained, from which a value could be obtained for the modulus of deformation in each test performed.
- This test was repeated with strands having a modified core wire according to the invention, but otherwise of the same dimensions. In each case, in a corresponding manner, a value for the modulus of deformation was determined.
- The values thus found by measurement and calculation for the modulus of deformation showed that in all cases with the use of modified core wires (and optionally modified outer wires) according to the invention a substantial increase of the modulus of deformation was found, while also the difference between the modulus of deformation and the modulus of elasticity became unimportant.
Claims (12)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT82201303T ATE28913T1 (en) | 1981-11-02 | 1982-10-20 | PRE-STRESSING CABLE FOR CONCRETE STRUCTURES AND CONCRETE STRUCTURES WITH SUCH CABLE. |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CH6966/81 | 1981-11-02 | ||
CH696681 | 1981-11-02 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0078564A2 true EP0078564A2 (en) | 1983-05-11 |
EP0078564A3 EP0078564A3 (en) | 1984-05-23 |
EP0078564B1 EP0078564B1 (en) | 1987-08-12 |
Family
ID=4317835
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP82201303A Expired EP0078564B1 (en) | 1981-11-02 | 1982-10-20 | Prestressing strand for concrete structures and concrete structures containing such strand |
Country Status (6)
Country | Link |
---|---|
EP (1) | EP0078564B1 (en) |
AT (1) | ATE28913T1 (en) |
DE (1) | DE3276952D1 (en) |
ES (2) | ES8500372A1 (en) |
FI (1) | FI72370C (en) |
NO (1) | NO165122C (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0110542A1 (en) * | 1982-10-28 | 1984-06-13 | Florida Wire And Cable Company | Concrete strengthening members, particularly prestressing tendons, having improved corrosion resistance and/or bonding characteristics, and methods relating thereto |
CN103374844A (en) * | 2012-04-12 | 2013-10-30 | 黑泽建设株式会社 | Double rustproof pc strand |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR1284364A (en) * | 1960-03-21 | 1962-02-09 | Tyler Wayne Res Corp | Stranded wire strand and method of treating wire |
GB1078184A (en) * | 1964-05-19 | 1967-08-02 | Halmstads Jaernverks Ab | Improvements relating to the production of a rough corrosionresistant surface on iron re-inforcing material |
GB1135491A (en) * | 1965-01-02 | 1968-12-04 | Intercontinentale Technik Ges | A prestressing element |
GB1194758A (en) * | 1967-10-04 | 1970-06-10 | Westfalische Drahtindustrie | Prestressed-Concrete Wire Strand |
US3755003A (en) * | 1970-07-24 | 1973-08-28 | Diamond Shamrock Corp | Method of preparing and using concrete reinforcing elements |
-
1982
- 1982-10-20 DE DE8282201303T patent/DE3276952D1/en not_active Expired
- 1982-10-20 EP EP82201303A patent/EP0078564B1/en not_active Expired
- 1982-10-20 AT AT82201303T patent/ATE28913T1/en not_active IP Right Cessation
- 1982-10-29 FI FI823701A patent/FI72370C/en not_active IP Right Cessation
- 1982-10-29 ES ES516971A patent/ES8500372A1/en not_active Expired
- 1982-11-01 NO NO823616A patent/NO165122C/en unknown
-
1983
- 1983-04-19 ES ES1983271531U patent/ES271531U/en active Pending
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR1284364A (en) * | 1960-03-21 | 1962-02-09 | Tyler Wayne Res Corp | Stranded wire strand and method of treating wire |
GB1078184A (en) * | 1964-05-19 | 1967-08-02 | Halmstads Jaernverks Ab | Improvements relating to the production of a rough corrosionresistant surface on iron re-inforcing material |
GB1135491A (en) * | 1965-01-02 | 1968-12-04 | Intercontinentale Technik Ges | A prestressing element |
GB1194758A (en) * | 1967-10-04 | 1970-06-10 | Westfalische Drahtindustrie | Prestressed-Concrete Wire Strand |
US3755003A (en) * | 1970-07-24 | 1973-08-28 | Diamond Shamrock Corp | Method of preparing and using concrete reinforcing elements |
Non-Patent Citations (2)
Title |
---|
HÜTTE, Bautechnik vol.1, page 726, * |
Techniques de l'Ingénieur, pages C-360-5 and 6 * |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0110542A1 (en) * | 1982-10-28 | 1984-06-13 | Florida Wire And Cable Company | Concrete strengthening members, particularly prestressing tendons, having improved corrosion resistance and/or bonding characteristics, and methods relating thereto |
CN103374844A (en) * | 2012-04-12 | 2013-10-30 | 黑泽建设株式会社 | Double rustproof pc strand |
EP2650431A3 (en) * | 2012-04-12 | 2014-03-05 | Kurosawa Construction Co., Ltd. | Corrosion resistant steel strand for prestressed concrete |
TWI477674B (en) * | 2012-04-12 | 2015-03-21 | Kurosawa Kensetsu Kk | Double rustproof pc strand |
Also Published As
Publication number | Publication date |
---|---|
NO823616L (en) | 1983-05-03 |
ES271531U (en) | 1983-10-16 |
NO165122C (en) | 1990-12-27 |
EP0078564B1 (en) | 1987-08-12 |
FI823701A0 (en) | 1982-10-29 |
EP0078564A3 (en) | 1984-05-23 |
ATE28913T1 (en) | 1987-08-15 |
ES516971A0 (en) | 1984-10-01 |
FI823701L (en) | 1983-05-03 |
FI72370C (en) | 1987-05-11 |
NO165122B (en) | 1990-09-17 |
FI72370B (en) | 1987-01-30 |
DE3276952D1 (en) | 1987-09-17 |
ES8500372A1 (en) | 1984-10-01 |
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