WO2008118686A1 - Hydraulic post tensioning jack - Google Patents

Hydraulic post tensioning jack Download PDF

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Publication number
WO2008118686A1
WO2008118686A1 PCT/US2008/057337 US2008057337W WO2008118686A1 WO 2008118686 A1 WO2008118686 A1 WO 2008118686A1 US 2008057337 W US2008057337 W US 2008057337W WO 2008118686 A1 WO2008118686 A1 WO 2008118686A1
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WO
WIPO (PCT)
Prior art keywords
plates
post tensioning
jack
hydraulic jack
cylinders
Prior art date
Application number
PCT/US2008/057337
Other languages
French (fr)
Inventor
Frantz Stanford
Original Assignee
Actuant Corporation
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Actuant Corporation filed Critical Actuant Corporation
Publication of WO2008118686A1 publication Critical patent/WO2008118686A1/en

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Classifications

    • 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
    • E04G21/121—Construction of stressing jacks

Definitions

  • This invention relates to hydraulic cylinder operated devices for tensioning reinforcement cables in green concrete, commonly referred to as post tensioning jacks, which are used to make pre-stressed concrete structures.
  • Pre-stressed concrete structures include spans of concrete and also building foundation slabs as are commonly used for residential and commercial building construction in the southern part of the United States.
  • Such pre-stressed concrete is made by running steel cables, known as strands, through a concrete form, pouring the concrete so that it encapsulates the strands, waiting a certain period for the concrete to partially cure, and then applying tension to the strands using a post tensioning jack.
  • One end of the strand extending beyond one end of the slab is secured to the slab, for example, with a plate and wedge or chuck that grips the strand and is anchored in the slab, and the other end of the strand extending beyond the other end of the slab is grasped by a gripper of the tensioning jack. Hydraulic pressure is then applied to the jack to create tension in the strand and a wedge or grommet is then applied to the end of the strand that bears against the plate or anchor at the end of the slab to hold the tension in the strand as the concrete fully cures thereafter.
  • Such systems are described, for example, in U.S. Patent No. 6,224,036 and 7,147,210, which are incorporated herein by reference for their disclosures of post tensioning jacks.
  • the jacks disclosed in these two patents each have two spaced apart hydraulic cylinders with the gripper, which may be a wedge or cone style gripper between the cylinders, that grasps the cable to exert tension thereon.
  • the two cylinders are fixed to one another by body or coupler elements and the gripper is fixed to one of the coupler elements.
  • the two pistons of the cylinders are fixed together at their ends by a yoke that has a nose that seats against a plate or other load bearing element at the end of the slab.
  • the two hydraulic cylinders are formed in a single piece of steel, so as to provide a jack body that is common to both cylinders, and a space is formed between the two cylinders in the jack body, which essentially amounts to a channel, in which the grippers reside and act.
  • the grippers are wedge or cone shaped with teeth on their inner sides that grip the cable, and an angled surface on their outsides that when the tension on the cable pulls the gripper, the grip on the cable increases by the wedging action of the grippers. This wedging action also creates a force against the inside surfaces of the cylinders that tends to wedge the cylinders apart.
  • the jack body has been made of a high strength steel material to resist the forces of the gripper on the cylinders.
  • High strength steel is, however, heavy and difficult to machine.
  • the machining required of the body is significant, as is the weight. Persons operating post tensioning jacks have to lift them manually and carry them from one pull to another, all day long sometimes. Therefore, a need exists for an improved post tensioning jack.
  • the invention provides a post tensioning jack with a jack body that is made of a composite construction.
  • the majority of the jack body is preferably a lower weight material, such as aluminum, that can be relatively easily machined to provide the long bores and other machined surfaces that are required in the jack body.
  • the jack body is formed with slots in which reinforcing plates are secured to stiffen the jack body against the forces imparted on it by the grippers.
  • the reinforcing plates are preferably made of a material of a higher stiffness than the material of the jack body. The plates reduce flexing of the jack body and thereby improve its fatigue life. Thereby, a jack body of reduced weight but sufficient strength and long life can be provided.
  • the plates are steel and may be adhesively bonded in place. Alternatively, the plates could be pinned, bolted or even cast in place.
  • At least some of the plates are U-shaped, having legs that extend into walls of the body on opposite sides of a channel and in which the gripper is received so as to react against the wedging forces exerted by the gripper.
  • Fig. 1 is a perspective view of a post tensioning jack incorporating the invention
  • Fig. 2 is a perspective view of the underside of the jack of Fig. 1
  • Fig 3 is a top plan view of the jack, with the handle broken away
  • Fig. 4 is a cross sectional view from the plane of the line 4-4 of Fig. 3
  • Fig. 5 is a cross sectional view from the plane of the line 5-5 of Fig. 4
  • Fig. 6 is a fragmentary sectional view from the plane of the line 6-6 of Fig. 4
  • Fig. 7 is a cross sectional view from the plane of the line 7-7 of Fig. 4.
  • a post tension jack 10 of the invention has a body 12 with two cylinders 14 and 16 spaced apart with a channel 18 between them.
  • the cylinders 14 and 16 connect to a first bridge 19 and a second bridge 21 that extend between them.
  • Cylinder rods 20 and 22 extend from the ends of the cylinders 14 and 16 and are attached to one another by a nose body 24.
  • the nose body 24 includes a power seater 26 that, as is well known in the art, is actuated at the end of the tensioning operation to seat the wedges that maintain tension in the cable after the jack 10 is removed from the cable.
  • the cylinder rods 20 and 22 extend in generally parallel directions. Referring to Figs. 3 and 7, the jack 10 has a longitudinal axis 27 that is also generally parallel to the direction in which the cylinder rods 20 and 22 extend.
  • Jack 10 also includes a handle 28 and hydraulic ports 30 and 32 that receive hydraulic fluid for extending and retracting the pistons 20 and 22.
  • a gripper 36 that includes two wedges 38 that slide in a wedge shaped cavity of the body 12 with wear plates 39 between the wedges 38 and the walls of the body 12.
  • the wedges 38 have teeth (not shown) on their inside faces so as to grip a cable placed between the wedges 38. When tension is placed on the cable, the cable pulls the wedges 38 toward the nose body 24 which tends to increase the grip of the gripper 36 on the cable but also wedges apart the cylinders 14 and 16.
  • the body 12 has slots 44 in which reinforcing plates 46 or 48 are received.
  • the slots 44 preferably span a space between the cylinders 14 and 16 and are preferably located in the first bridge 19 of the body 12.
  • the slots 44 are also preferably spaced apart from one another generally in the direction of the longitudinal axis 27 of the body 12.
  • the U- shaped plates 46 are received in the 8 slots 44 that are closest to the nose body 24 and the rectangular plates 48 are received in the 2 slots 44 that are the furthest from the nose body 24.
  • the wedge shape of the channel 18 is too wide to permit the legs of plates 46 to extend into the walls of the body 12.
  • Each slot matches the shape of the plate received in the slot, so there are eight U-shaped slots and two rectangular slots.
  • the plates 46 define a rectangular area into which the gripper 36 partially extends. That is, the area defined by the plates 46 longitudinally overlaps the gripper 36.
  • the plates 46 and 48 may be secured in the slots 44 with an adhesive, for example, Loctite 680TM, or by mechanical fasteners such as pins or bolts. Alternatively, it may be possible to cast the plates 46 and 48 in place. As a further alternative, the plates 46 may be secured in the slots 44 by press fitting. Specifically, the surfaces of the legs near the gripper 36 on the inside of the U-shape may be received in the body 12 with a press fit.
  • the body 12 may be made of a material such as a high strength aluminum, for example, 7075 aluminum alloy, or another high strength, high stiffness, low weight (compared to steel) material.
  • a material such as a high strength aluminum, for example, 7075 aluminum alloy, or another high strength, high stiffness, low weight (compared to steel) material.
  • titanium, reinforced plastic, or possibly other materials could advantageously be applied.
  • the plates 46 and 48 are made of a material that has a higher stiffness than the material of the body 12, such as steel.
  • the plates 46 and 48 are received in the openings 44 with a fit and/or connection so that the plates 46 and 48 help bear the loads exerted by the gripper 36 that tend to separate the cylinders 14 and 16.
  • the forces exerted by the gripper 36 on the cylinders 14 and 16 create a moment that tends to rotate the two cylinders 14 and 16 apart.
  • the forces exerted on the gripper 36 pull the gripper 36 further into the area defined by the plates 46 when the post tensioning hydraulic jack tensions a cable.
  • the U-shaped plates 46 with their legs extending into the walls of the body 12 on opposite sides of the gripper 36 are particularly adapted to counteract the forces exerted by the gripper 36 and prevent the gripper 36 from deflecting the body 12. This contributes to increase the fatigue strength and life of the body 12, to permit using lighter weight and more machinable materials.

Abstract

A post tensioning hydraulic jack for tensioning a strand in prestressed concrete has two cylinders in a common body with stiffening plates in slots of the body that span a space between the cylinders in which a gripper resides.

Description

HYDRAULIC POST TENSIONING JACK
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional Patent Application No. 60/896,415 filed March 22, 2007, which is hereby incorporated by reference.
STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
FIELD OF THE INVENTION
[0003] This invention relates to hydraulic cylinder operated devices for tensioning reinforcement cables in green concrete, commonly referred to as post tensioning jacks, which are used to make pre-stressed concrete structures.
BACKGROUND OF THE INVENTION
[0004] Pre-stressed concrete structures include spans of concrete and also building foundation slabs as are commonly used for residential and commercial building construction in the southern part of the United States. Such pre-stressed concrete is made by running steel cables, known as strands, through a concrete form, pouring the concrete so that it encapsulates the strands, waiting a certain period for the concrete to partially cure, and then applying tension to the strands using a post tensioning jack. One end of the strand extending beyond one end of the slab is secured to the slab, for example, with a plate and wedge or chuck that grips the strand and is anchored in the slab, and the other end of the strand extending beyond the other end of the slab is grasped by a gripper of the tensioning jack. Hydraulic pressure is then applied to the jack to create tension in the strand and a wedge or grommet is then applied to the end of the strand that bears against the plate or anchor at the end of the slab to hold the tension in the strand as the concrete fully cures thereafter. Such systems are described, for example, in U.S. Patent No. 6,224,036 and 7,147,210, which are incorporated herein by reference for their disclosures of post tensioning jacks.
[0005] The jacks disclosed in these two patents each have two spaced apart hydraulic cylinders with the gripper, which may be a wedge or cone style gripper between the cylinders, that grasps the cable to exert tension thereon. The two cylinders are fixed to one another by body or coupler elements and the gripper is fixed to one of the coupler elements. The two pistons of the cylinders are fixed together at their ends by a yoke that has a nose that seats against a plate or other load bearing element at the end of the slab.
[0006] hi other constructions, the two hydraulic cylinders are formed in a single piece of steel, so as to provide a jack body that is common to both cylinders, and a space is formed between the two cylinders in the jack body, which essentially amounts to a channel, in which the grippers reside and act. The grippers are wedge or cone shaped with teeth on their inner sides that grip the cable, and an angled surface on their outsides that when the tension on the cable pulls the gripper, the grip on the cable increases by the wedging action of the grippers. This wedging action also creates a force against the inside surfaces of the cylinders that tends to wedge the cylinders apart. As a result, the jack body has been made of a high strength steel material to resist the forces of the gripper on the cylinders. High strength steel is, however, heavy and difficult to machine. The machining required of the body is significant, as is the weight. Persons operating post tensioning jacks have to lift them manually and carry them from one pull to another, all day long sometimes. Therefore, a need exists for an improved post tensioning jack.
SUMMARY OF THE INVENTION
[0007] The invention provides a post tensioning jack with a jack body that is made of a composite construction. The majority of the jack body is preferably a lower weight material, such as aluminum, that can be relatively easily machined to provide the long bores and other machined surfaces that are required in the jack body. In addition, the jack body is formed with slots in which reinforcing plates are secured to stiffen the jack body against the forces imparted on it by the grippers. The reinforcing plates are preferably made of a material of a higher stiffness than the material of the jack body. The plates reduce flexing of the jack body and thereby improve its fatigue life. Thereby, a jack body of reduced weight but sufficient strength and long life can be provided.
[0008] hi one preferred form, the plates are steel and may be adhesively bonded in place. Alternatively, the plates could be pinned, bolted or even cast in place.
[0009] hi another preferred aspect, at least some of the plates are U-shaped, having legs that extend into walls of the body on opposite sides of a channel and in which the gripper is received so as to react against the wedging forces exerted by the gripper. [0010] The foregoing and other objects and advantages of the invention will appear in the detailed description which follows, hi the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Fig. 1 is a perspective view of a post tensioning jack incorporating the invention; [0012] Fig. 2 is a perspective view of the underside of the jack of Fig. 1; [0013] Fig 3 is a top plan view of the jack, with the handle broken away; [0014] Fig. 4 is a cross sectional view from the plane of the line 4-4 of Fig. 3; [0015] Fig. 5 is a cross sectional view from the plane of the line 5-5 of Fig. 4; [0016] Fig. 6 is a fragmentary sectional view from the plane of the line 6-6 of Fig. 4; and [0017] Fig. 7 is a cross sectional view from the plane of the line 7-7 of Fig. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0018] Referring to Fig. 1, a post tension jack 10 of the invention has a body 12 with two cylinders 14 and 16 spaced apart with a channel 18 between them. The cylinders 14 and 16 connect to a first bridge 19 and a second bridge 21 that extend between them. Cylinder rods 20 and 22 extend from the ends of the cylinders 14 and 16 and are attached to one another by a nose body 24. The nose body 24 includes a power seater 26 that, as is well known in the art, is actuated at the end of the tensioning operation to seat the wedges that maintain tension in the cable after the jack 10 is removed from the cable. The cylinder rods 20 and 22 extend in generally parallel directions. Referring to Figs. 3 and 7, the jack 10 has a longitudinal axis 27 that is also generally parallel to the direction in which the cylinder rods 20 and 22 extend.
[0019] Jack 10 also includes a handle 28 and hydraulic ports 30 and 32 that receive hydraulic fluid for extending and retracting the pistons 20 and 22. Referring particularly to Figs. 2, 4 and 7, in the channel 18 resides a gripper 36 that includes two wedges 38 that slide in a wedge shaped cavity of the body 12 with wear plates 39 between the wedges 38 and the walls of the body 12. The wedges 38 have teeth (not shown) on their inside faces so as to grip a cable placed between the wedges 38. When tension is placed on the cable, the cable pulls the wedges 38 toward the nose body 24 which tends to increase the grip of the gripper 36 on the cable but also wedges apart the cylinders 14 and 16.
[0020] To counteract the force exerted on the body 12 by the gripper 36, the body 12 has slots 44 in which reinforcing plates 46 or 48 are received. As shown in Fig. 1, the slots 44 preferably span a space between the cylinders 14 and 16 and are preferably located in the first bridge 19 of the body 12. The slots 44 are also preferably spaced apart from one another generally in the direction of the longitudinal axis 27 of the body 12. As shown in Fig. 4, the U- shaped plates 46 are received in the 8 slots 44 that are closest to the nose body 24 and the rectangular plates 48 are received in the 2 slots 44 that are the furthest from the nose body 24. This is because where the two rectangular plates 48 are received, the wedge shape of the channel 18 is too wide to permit the legs of plates 46 to extend into the walls of the body 12. Each slot matches the shape of the plate received in the slot, so there are eight U-shaped slots and two rectangular slots. As shown in Fig. 7, the plates 46 define a rectangular area into which the gripper 36 partially extends. That is, the area defined by the plates 46 longitudinally overlaps the gripper 36.
[0021] The plates 46 and 48 may be secured in the slots 44 with an adhesive, for example, Loctite 680™, or by mechanical fasteners such as pins or bolts. Alternatively, it may be possible to cast the plates 46 and 48 in place. As a further alternative, the plates 46 may be secured in the slots 44 by press fitting. Specifically, the surfaces of the legs near the gripper 36 on the inside of the U-shape may be received in the body 12 with a press fit.
[0022] The body 12 may be made of a material such as a high strength aluminum, for example, 7075 aluminum alloy, or another high strength, high stiffness, low weight (compared to steel) material. For example, titanium, reinforced plastic, or possibly other materials could advantageously be applied. The plates 46 and 48 are made of a material that has a higher stiffness than the material of the body 12, such as steel.
[0023] The plates 46 and 48 are received in the openings 44 with a fit and/or connection so that the plates 46 and 48 help bear the loads exerted by the gripper 36 that tend to separate the cylinders 14 and 16. The forces exerted by the gripper 36 on the cylinders 14 and 16 create a moment that tends to rotate the two cylinders 14 and 16 apart. However, the forces exerted on the gripper 36 pull the gripper 36 further into the area defined by the plates 46 when the post tensioning hydraulic jack tensions a cable. The U-shaped plates 46 with their legs extending into the walls of the body 12 on opposite sides of the gripper 36 are particularly adapted to counteract the forces exerted by the gripper 36 and prevent the gripper 36 from deflecting the body 12. This contributes to increase the fatigue strength and life of the body 12, to permit using lighter weight and more machinable materials.
[0024] A preferred embodiment of the invention has been described in considerable detail. Many modifications and variations to the preferred embodiment described will be apparent to a person of ordinary skill in the art. Therefore, the invention should not be limited to the embodiment described.

Claims

I claim:
1. In a post tensioning hydraulic jack that has two parallel spaced apart hydraulic cylinders with a common body and a gripper between the cylinders that exerts a force on the cylinders that tends to flex the cylinders apart, the improvement wherein the body is made of a first material of a first stiffness and has slots in it that span a space between the cylinders and in which reinforcing plates of a second material of a second stiffness are received, wherein the second stiffness is greater than the first stiffness.
2. A post tensioning hydraulic jack as in claim 1, wherein the plates are steel.
3. A post tensioning hydraulic jack as in claim 1, wherein the plates are adhesively bonded to the body in the slots.
4. A post tensioning hydraulic jack as in claim 1, wherein the plates are mechanically fastened to the body in the slots.
5. A post tensioning hydraulic jack as in claim 1, wherein the plates are cast into the slots in the body.
6. A post tensioning hydraulic jack as in claim 1, wherein the plates are press-fitted into the slots in the body.
7. A post tensioning hydraulic jack as in claim 1, wherein the slots are shaped to match the shape of the plates.
8. A post tensioning hydraulic jack as in claim 1, wherein the plates define an area that is longitudinally overlapped by the gripper.
9. A post tensioning hydraulic jack as in claim 8, wherein the gripper is pulled further into the area defined by the plates when the post tensioning hydraulic jack tensions a cable.
10. A post tensioning hydraulic jack as in claim 1, wherein the plates are included on a first bridge of the body, and wherein the body includes a second bridge that is spaced apart from the first bridge in the direction of a longitudinal axis of the body of the jack.
11. A post tensioning hydraulic jack as in claim 1 , wherein the plates are spaced apart generally in a direction parallel to a longitudinal axis of the body of the jack.
12. A post tensioning hydraulic jack as in claim 1, wherein at least some of the plates are U-shaped.
13. A post tensioning hydraulic jack as in claim 12, wherein at least some of the plates are U-shaped as viewed in a direction parallel to a longitudinal axis of the body of the jack.
14. A post tensioning hydraulic jack as in claim 12, wherein at least some of the plates are U-shaped and at least some of the plates are rectangular.
15. A post tensioning hydraulic jack as in claim 12, wherein legs of the U-shaped plates extend into walls of the body on opposite sides of the gripper.
16. In a post tensioning jack that includes a body and a nose body, the body including two hydraulic cylinders disposed at opposite ends of the body and further including a surface defining a channel disposed between the two cylinders, the two cylinders each having a cylinder rod that translates relative to the cylinders and the body and connects to the nose body, the post tensioning jack further including a gripper disposed in the channel that reacts against sides of the channel and grips a cable tensioned by the post tension jack, the improvement wherein: the body is made of a first material of a first stiffness and includes at least one slot, the at least one slot accommodating a plate that resists a reaction of the wedge against the channel, wherein the plate is made of a second material of a second stiffness, and wherein the second stiffness is greater than the first stiffness.
17. A post tensioning jack as in claim 16, wherein the plate is adhesively bonded to the body in the at least one slot.
18. A post tensioning jack as in claim 16, wherein the plate is mechanically fastened to the body in the at least one slot.
19. A post tensioning jack as in claim 16, wherein the plate is cast into the at least one slot in the body.
20. A post tensioning jack as in claim 16, wherein the plate is press-fitted into the at least one slot in the body.
PCT/US2008/057337 2007-03-22 2008-03-18 Hydraulic post tensioning jack WO2008118686A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US89641507P 2007-03-22 2007-03-22
US60/896,415 2007-03-22

Publications (1)

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WO2008118686A1 true WO2008118686A1 (en) 2008-10-02

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103143647A (en) * 2013-01-23 2013-06-12 林小平 Micro-scale shaft cutting die
EP3312363A1 (en) * 2016-10-18 2018-04-25 Felix L. Sorkin Lightweight jack

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4598897A (en) * 1984-02-16 1986-07-08 Aktiebolaget Bygg -Och Transportekonomi (Bt) Div. Nike Hydraulics Hydraulic tensioning tool
US6224036B1 (en) * 1997-01-17 2001-05-01 Applied Power Inc. Concrete reinforcement cable tensioner
KR200354900Y1 (en) * 2004-04-19 2004-06-30 오원석 lengthen device
US7147210B2 (en) * 2004-02-02 2006-12-12 Actuant Corporation Cable tensioning system and method of operation

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4598897A (en) * 1984-02-16 1986-07-08 Aktiebolaget Bygg -Och Transportekonomi (Bt) Div. Nike Hydraulics Hydraulic tensioning tool
US6224036B1 (en) * 1997-01-17 2001-05-01 Applied Power Inc. Concrete reinforcement cable tensioner
US7147210B2 (en) * 2004-02-02 2006-12-12 Actuant Corporation Cable tensioning system and method of operation
KR200354900Y1 (en) * 2004-04-19 2004-06-30 오원석 lengthen device

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103143647A (en) * 2013-01-23 2013-06-12 林小平 Micro-scale shaft cutting die
EP3312363A1 (en) * 2016-10-18 2018-04-25 Felix L. Sorkin Lightweight jack

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