Classifications

• • 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
  • E04C5/12—Anchoring devices
• • 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
  • E04C5/12—Anchoring devices
  • E04C5/122—Anchoring devices the tensile members are anchored by wedge-action
• • E—FIXED CONSTRUCTIONS
  • E04—BUILDING
  • E04G—SCAFFOLDING; FORMS; SHUTTERING; BUILDING IMPLEMENTS OR AIDS, OR THEIR USE; HANDLING BUILDING MATERIALS ON THE SITE; REPAIRING, BREAKING-UP OR OTHER WORK ON EXISTING BUILDINGS
  • E04G21/00—Preparing, conveying, or working-up building materials or building elements in situ; Other devices or measures for constructional work
  • E04G21/12—Mounting of reinforcing inserts; Prestressing

Definitions

• Anchorage assembly for a structure concrete structure with such an assembly, and manufacturing method of such a concrete structure
• the present invention concerns an anchorage assembly for a concrete structure, a concrete structure with such an assembly, and a manufacturing method of such a concrete structure.
• the tendons are made of individual steel elements that are placed in the structure at a first stage and stressed to a certain force at a later stage.
• bonded systems In bonded systems, one or more strands are inserted into a metal or plastic channel that is embedded in the concrete. The strand(s) is(are) stressed with a mono or multi-strand jack and anchored in a common anchorage device. The channel is then filled with a cementitious grout that provides corrosion protection to the strand(s) and bonds the tendon to the concrete surrounding the channel. Bonded systems are more commonly used in bridges for the roadway, the piles, the foundation and in building. In buildings, they are typically used in heavily loaded beams such as transfer girders and landscaped plaza decks. [0004] An unbonded tendon is one in which the prestressing steel is not actually bonded to the concrete that surrounds it except at the anchorages.
• the two most common unbonded systems are first monostrand tendons and secondly bare strands surrounded by grease.
• the monostrands are used in slabs and beams for buildings, parking structures and-on-ground, in bridge for external post-tensioning and in several type of a suspended structure with cable stay.
• a monostrand consists of several steel wires that are coated with a corrosion-inhibiting soft product and encased in an extruded plastic protective sheathing made of plastic material. Then the tendon can be made of one monostrand (for slab) up to several
• monostrands external post-tensioning ,cable stays
• the monostrand(s) is (are) directly embedded in the concrete; in another case they may be installed in a channel.
• the second type of unbonded tendon consists in one to several bare strands that are installed in a channel made of steel or plastic, the channel being embedded in a concrete structure or following a specific layout within a structure.
• the void is filled with a corrosion-inhibiting soft product allowing the strand to move with respect to the channel and to the structure.
• the bare strands consist of several steel wires assembled
• the anchorage consists of an iron casting and a conical, two-piece or three- piece wedge which grips individually from 1 to 6 or 7 strands.
• an anchor block with two-piece or three-piece wedges, which grips as many strands as necessary.
• Such anchor block bears on a cast iron piece or steel manufactured part that is embedded in a structure.
• the channel is generally made of plastic or steel tubes when located outside a structure between several deviation point, and the channel is generally made of corrugated ducts in steel or plastic when embedded in a structure.
• EP0566463 presents such an unbonded system with monostrands, in a modified embodiment where the strands of the tendon are embedded directly in the concrete block forming the concrete structure or in a channel filled with a hardening filler such as cement grout before the strands are stressed.
• the advantage of such unbonded system is that the steel wires inside the monostrand are protected from any corrosion by the soft filler contained in the plastic sheath. Also the sheath allows to carry out the installation of the strands much in advance during the construction period, reducing therefore the total time of construction with a high level of protection.
• the present invention also aims to provide an alternative solution to the known solution which facilitates inspection and re-stressing of the tendons.
• an anchorage assembly for a structure comprising a tendon made of strands, the anchorage assembly defining at least two parts:
• said second part is placed within a structure, with the strands having said end portion passed through on one hand an opening formed in a bearing plate disposed within the structure in an adjacent position to the first tubular member outlet, with said first tubular member outlet and said opening connected to each other, and on the other hand said individual perforations of said anchor head which is placed outside of the front face of the structure,
• the anchor head has an outside diameter smaller than the diameter of said opening of the bearing plate.
• the anchorage assembly further comprises a removable locking system interposed between said anchor head and said bearing plate, the presence of the locking system preventing thereby the anchor head to enter said opening and said second tubular member outlet.
• the second part can be placed within a formwork intended to receive the concrete forming the concrete structure.
• the de- tensioning of the tendon can be implemented while the anchor head has entered within the first tubular member, after removal of the locking system.
• Fig. 1 shows a schematic longitudinal view of an embodiment of the anchorage assembly in a first step, the upper part being a section and the lower part being outside view, when the strands have been installed in the channel and in the different tubular parts without any anchorage accessories,
• Fig.2 shows the same view of the anchorage assembly of Fig.1 , in a further step including injection of a filler compound in the third part,
• Fig. 3 illustrates the same anchorage assembly after mounting of the locking device, with a schematic representation of jack that is applying a force to the tendon,
• Fig.4 illustrates the same anchorage assembly as it would remain during the normal life of the structure with a cap protecting the protruding area of the tendon and a filler protecting the bare strands in the first tubular part and rigid filler in the second tubular part around the
• FIG. 5 schematically shows a first type of surveillance operation of the tendon
• Fig.6 schematically shows another second type of surveillance operation of the tendon.
• Fig.1 In Fig.1 is shown a situation where the tendon 10 is mounted through an anchorage assembly 20 placed partially within a structure 42, and comprising in a linear arrangement a channel 43, a second tubular member 22, a first tubular member 24 and a bearing plate 26.
• the second tubular member 22 is placed within the structure 42 at a distance from the front face 40 of the structure, in a direction orthogonal to the front face 40.
• the inner diameter of the second tubular member 22 allows the introduction of the tendon 10.
• the inner diameter of the second tubular member 22 is D1.
• the first tubular member 24 extends the second tubular member 22 in a coaxial manner to the first tubular member 22, in the direction of the orthogonal to the front face 40.
• Such a first tubular member 24 is usually formed by a trumpet shape elongated member, named as a
• the inlet of the first tubular member 24 is connected in a water-sealed manner to the outlet of the second tubular member 22.
• the inner diameter of the first tubular member 24 also allows the introduction of the tendon 10.
• the inner diameter of the first tubular member 24 is larger than the inner diameter of the second tubular member 22.
• at least the inner diameter D2 of the first tubular member 24 at the inlet side is larger than the inner diameter of the second tubular member 22 D1 at the outlet side, namely D2 > D1.
• the bearing plate 26 is placed at the front face 40 of the structure 42, with a large opening 27 adjacent to the outlet of the first tubular member 24 (see Fig.1), having an inner diameter D4 close to D3.
• an injection pipe 23 is mounted so as to have fluid communication between the inner space of the second tubular member 22 and the outside of the formwork forming the front face 40 of the structure 42.
• a temporary sealing block 28 having an outer diameter close to D2 but slightly less, is threaded from outside the anchorage assembly 20, into the bearing plate 26 and the first tubular member 24 up to the inlet of the first tubular member 22 onto an abutment plate 41 with an opening.
• Such a temporary sealing block 28 forms a thick plate having as much holes as strands 12 and is first placed with the tendon passing through, each strand 12 in a corresponding hole of said temporary sealing block 28, before engagement of the temporary sealing block 28 through the opening 27 of the bearing plate 26.
• the sealing block 28 is made of a sealing pad locked between a pressing pad and a pressing plate.
• WO201 1 1 16828 presents a possible embodiment for such a sealing block 28.
• the tendon 10 is composed of one or a plurality of sheathed and greased strands 12 with sheath 14 within the structure 42 up to the outlet face defined by the abutment plate 41.
• the strand(s) is (are) individually wrapped in a outer (Plastic) sheath 14 with interposition of corrosion preventive compound such as grease or wax, which means the metallic strand can slide with respect to the sheath forming the envelope 14 of each strand 12, the corrosion preventive compound forming also a lubricant.
• corrosion preventive compound such as grease or wax
• the preferred thickness of the sheaths 14 is between 1 and 2 mm, a value over 1.5 mm is recommended when the tendon length is over 100 m long of the installation condition are difficult with the tendon deviation having high deviation ( over 100 °).
• the invention is not limited to such preferred type of strands 12 and can apply also to other types of strands, such as bare metallic strands (not illustrated) : in such a case, the second tubular member 22 is not to be filed in with cement matrix but with a non-hardening corrosion preventive compound such as wax or grease.
• the second tubular member 22 is filled with a hardening filler by injection of a hardening matrix through the injection pipe 23 into the second tubular member 22 so as to fill in all the interstices between the outer sheath 14 and the second tubular member 22, and between all pairs of adjacent sheathed strands 12.
• a hardening matrix By the setting or hardening of the cement matrix 23a, each strand 12 is locked in a direction perpendicular to the front face of the anchorage 40 by its sheath 14 to the second tubular member 22.
• the temporary sealing block 28 is un-tight and removed.
• an anchor head 30 and a removable locking system 32 are provided.
• the anchor head 30 is formed by a thick metallic block having as much holes as strands 12. According to an important feature, the anchor head 30 has an outside diameter D5 smaller than said opening (diameter D4) of the bearing plate 26 (see Fig. 3). Also, the outer end of the second tubular member 22 has a diameter D1 smaller than the outer diameter D5 of the anchor head 30. Also, the anchor head 30 has an outside diameter D5 smaller than said inner diameter D3 and D2 of the first tubular member 24 at the outlet side.
• the removable locking system 32 comprises at least one split shim; in Fig.1 two superposed split shims are used, having both an outer diameter larger than the diameter D4 of the opening of the bearing plate 26.
• the removable locking system 32 allows for the reversible locking of the anchor head 30 outside the first tubular member 24 (for tensioning or re-tensioning the tendon 10) and, by unlocking, letting the anchor head 30 circulating in the first tubular member 24 (for de- tensioning the tendon 10) without removing the conical wedges 34.
• strands 12 are sheathed along their running part up to and within said second tubular member 22, said sheath 14 being thereby able to be embedded within said filler compound (notably locked within cement matrix 23a) in said second tubular member 22, and the sheaths 14 of the said strands 12 are removed in their intermediate and end portions
• unsheathing operation is generally carried out just before the third step of stressing described below so that the strands are protected from the corrosion until they are unsheathed and finally stressed.
• a cap 36 is mounted in a water-tight manner onto the bearing plate 26, for accommodating said removable locking element 32, said anchor head 30 and said end portion of the tendon 10 (the extremity of the strands 12 of the end portion being unsheathed). Said cap 36 is able to receive a removable protective product, namely a non-hardening corrosion preventive compound 38, such as wax or grease.
• the anchorage assembly 20 of the preferred embodiment of the present invention defines, as shown on Fig.4, a first part C, a second part B and a third part A.
• the strands 12 are locked by their sheath 14 with respect to the second tubular member 22, by means of the cement matrix 23a, with the possibility for the individual metallic strands to slide with respect to the corresponding sheath 14.
• the intermediate unsheathed portion 12a of the strands 12 is protected against corrosion by the corrosion preventive compound 38 contained in the second tubular element 24 .
• the third part A and the second part B are located within the structure 42.
• the end portion of the unsheathed strands 12a is placed in the removable locking system 32, the anchor head 30 and in the cap 36.
• the third part A of the anchorage assembly is omitted, namely the second tubular member 22 and the channel 43 are not present in the anchorage assembly 20.
• said sealing block 28 and said abutment plate 41 are placed during concreting and said strands 12 are able to be directly embedded in the structure concrete 42 by their sheath 14 while allowing the metallic part of the strand to move longitudinally in the structure.
• the strands remain locked laterally by the concrete matrix.
• Said strands could be monostrands.
• the strands 12 are in the normal service situation, namely after stressing and filling of the second tubular element 24 and of the cap 36 with grease or any other non-hardening corrosion preventive compound 38 which is in contact with the bare segment 12a of the strands 12.
• this corrosion preventive compound 38 is also present in the opening 27 of the bearing plate 26 around the tendon 10, namely between all pairs of adjacent bare strands 12a, between the periphery of the opening 27 and the periphery of the tendon 10, in the opening of the removable locking system 32 and in the perforations of the anchor head 30 so as to wrap all the unsheathed portions 12a of the strands 12.
• said first part C further comprises immobilisation pieces placed individually around a length of said unsheathed strands 12a at least partially disposed within the outlet of said perforations of the anchor head 30.
• said immobilisation pieces are split wedges 34.
• tendon 10 and the compound 23a can therefore be implanted as from the situation shown in fig.2 at any time, namely several weeks, months or years later: with its strands 12 and their sheath 14 the tendon 10 is protected against corrosion all along its length before removing the sheaths 14 and further stressing.
• the present invention concerns a method of lifting-off of the tendon 10 equipped with the previously described anchorage assembly 20, in a structure 42, and also a method for the surveillance of the tendon in such a structure 42.
• the structure 42 can be a structure made of concrete or steel or with both materials.
• such a method of lifting-off a tendon 10 in a structure 42 comprises a lift-off step of at least one tendon 10 with the following sub-steps:
• the outer radial face of the anchor head is threaded so as to cooperate with a complementary thread of the tension measuring device.
• the cap 36 cover the outer part of the block or anchor head 30 ( as shown in Fig. 4) then it is beforehand removed to give an access to the anchor head 30.
• a method of surveillance of a tendon 10 in a structure comprising a strand sampling step with the following sub-steps:
• said strand sampling step comprises further the following sub-steps (not shown):

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• Architecture (AREA)
• Civil Engineering (AREA)
• Structural Engineering (AREA)
• Mechanical Engineering (AREA)
• Reinforcement Elements For Buildings (AREA)

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• 2016
  • 2016-06-30 WO PCT/IB2016/053935 patent/WO2017002069A1/en not_active Ceased
  • 2016-06-30 KR KR1020177036551A patent/KR20180026394A/ko not_active Withdrawn
  • 2016-06-30 EP EP16738224.1A patent/EP3317471B1/de active Active

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