US3388810A - Device for extending and folding back masts or towers applicable to cranes and the like - Google Patents

Device for extending and folding back masts or towers applicable to cranes and the like Download PDF

Info

Publication number
US3388810A
US3388810A US617266A US61726667A US3388810A US 3388810 A US3388810 A US 3388810A US 617266 A US617266 A US 617266A US 61726667 A US61726667 A US 61726667A US 3388810 A US3388810 A US 3388810A
Authority
US
United States
Prior art keywords
section
mast
platform
sections
cranes
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.)
Expired - Lifetime
Application number
US617266A
Inventor
Durand Pierre
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Richier SA
Original Assignee
Richier SA
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 Richier SA filed Critical Richier SA
Application granted granted Critical
Publication of US3388810A publication Critical patent/US3388810A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B66—HOISTING; LIFTING; HAULING
    • B66C—CRANES; LOAD-ENGAGING ELEMENTS OR DEVICES FOR CRANES, CAPSTANS, WINCHES, OR TACKLES
    • B66C23/00—Cranes comprising essentially a beam, boom, or triangular structure acting as a cantilever and mounted for translatory of swinging movements in vertical or horizontal planes or a combination of such movements, e.g. jib-cranes, derricks, tower cranes
    • B66C23/18—Cranes comprising essentially a beam, boom, or triangular structure acting as a cantilever and mounted for translatory of swinging movements in vertical or horizontal planes or a combination of such movements, e.g. jib-cranes, derricks, tower cranes specially adapted for use in particular purposes
    • B66C23/26—Cranes comprising essentially a beam, boom, or triangular structure acting as a cantilever and mounted for translatory of swinging movements in vertical or horizontal planes or a combination of such movements, e.g. jib-cranes, derricks, tower cranes specially adapted for use in particular purposes for use on building sites; constructed, e.g. with separable parts, to facilitate rapid assembly or dismantling, for operation at successively higher levels, for transport by road or rail
    • B66C23/34—Self-erecting cranes, i.e. with hoisting gear adapted for crane erection purposes
    • B66C23/342—Self-erecting cranes, i.e. with hoisting gear adapted for crane erection purposes with telescopic elements
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04H—BUILDINGS OR LIKE STRUCTURES FOR PARTICULAR PURPOSES; SWIMMING OR SPLASH BATHS OR POOLS; MASTS; FENCING; TENTS OR CANOPIES, IN GENERAL
    • E04H12/00—Towers; Masts or poles; Chimney stacks; Water-towers; Methods of erecting such structures
    • E04H12/18—Towers; Masts or poles; Chimney stacks; Water-towers; Methods of erecting such structures movable or with movable sections, e.g. rotatable or telescopic
    • E04H12/187—Towers; Masts or poles; Chimney stacks; Water-towers; Methods of erecting such structures movable or with movable sections, e.g. rotatable or telescopic with hinged sections
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04H—BUILDINGS OR LIKE STRUCTURES FOR PARTICULAR PURPOSES; SWIMMING OR SPLASH BATHS OR POOLS; MASTS; FENCING; TENTS OR CANOPIES, IN GENERAL
    • E04H12/00—Towers; Masts or poles; Chimney stacks; Water-towers; Methods of erecting such structures
    • E04H12/34—Arrangements for erecting or lowering towers, masts, poles, chimney stacks, or the like

Definitions

  • ABSTRACT OF THE DISCLOSURE A hoisting appliance having an erectable mast transported reclining on a platform and made of two telescoped sections, one of which has one of its sides pivotally connected to the platform about a horizontal axis, while the other has its opposite side pivotally connected to the end of a link member hingedly connected to the platform, whereby bodily pivoting the telescoped sections about the hinge axis of the first section on the platform causes translation of the two sections relatively to each other.
  • the mast or jib consists of two telescoped sections, of which one has one side pivotally connected to the erecting platform about a horizontal axis, while the other has its side remote from the aforementioned side pivotally connected to the end of a link member hingedly connected to the platform about a horizontal axis, whereby a motion of the two telescoped sections relatively to each other, resulting from a force exerted between the two sections, will, depending on the direction in which the force is exerted, cause either the folded reclining mast to be moved into the vertical extended position, or conversely the vertically extended mast to be moved into its retracted horizontal position.
  • FIGURES 1, 2 and 3 are side elevation views of an embodiment of the invention as applied to a building crane, showing three different operative positions thereof;
  • FIGURE 4 shows an embodiment of control means utilizing a central jack
  • FIGURE 5 shows an alternative form of embodiment.
  • FIG. 1 shows a building crane the mast of which comprises a base 1 attached to a platform 2, on which said base is either reclining for transport as shown in FIGURE 1, or erected in the vertical position for operation of the crane as shown in FIGURE 3.
  • Platform 2 is fitted with wheels 3 to enable it to be moved, and also with bracing means (not shown) such as jack means to immobilize it on a chosen location.
  • the base 1 is made up of two sections 4 and 5 placed one within the other and devised for mutual telescoping movement.
  • guide wheels (not shown) could be carried by the inner section 5 and roll on guideways on the outer section 4.
  • the sections 4 and 5 are assumed to be of square or rectangular cross-section but could obviously have any convenient cross-sectional shape.
  • Sections 4 and 5 are further assumed to be lattice sections, as is customary in crane mast on jib construction.
  • Inner section 5 is pivotally connected to platform 2 about a horizontal axis b along that of its edges perpendicular to the longitudinal axis of platform 2 which is applied against the latter when the base is reclining (FIG- URE 1), while outer section 4 has its opposite side pivotally connected about an axis 7 to the end of two links 8 positioned symmetrically with respect to the longitudinal centerline of platform 2.
  • These links which merge together on the drawing (but which could be replaced by a frame) are hingedly connected to platform 2 about a horizontal axis 9.
  • the hinge axes 6 and 9 on platform 2 are sufficiently spaced for inner mast section 5 to be able to come to bear against the platform between these axes when it is in the erected position shown in FIGURE 3.
  • a force generating mechanism such as a hydraulic jack, screw jack, reeving system, rack device, or the like, acting on one hand against outer section 4 and on the other against inner section 5, enables opposed forces to be exerted thereagainst which are effective in moving the mast either from its reclining position shown in FIGURE 1 to its vertical position shown in FIGURE 3, or vice versa.
  • This. mechanism may be positioned in the interval between sections 4 and 5, or centrally, or entirely external to sections 4 and 5, its location being such that the direction of the force it exerts passes above axis 6 whereby to produce a rotating moment thereabout.
  • the force generating mechanism connected between sections 4 and 5 to be of the positive type, i.e. a jack or rack mechanism rather than a reeving system, in order to avoid uncontrolled terminal motion and ensuing shock loadings as the inner section 5 of the mast base contacts platform 2.
  • outer telescoping section 4 is formed with a bevelled end 10 which is pivotally connected to the links 8. As the figure shows, this ensures that this end is always located above and behind hinge axis 6 and does not therefore hinder initiation of the pivotal motion; further the hinge points 7 are located above and between axes 6 and 9, which is preferable for eificient operation.
  • locking means may be provided in order to unite sections 4 and 5 after the mast has been erected into the position in FIGURE 3.
  • the force generating mechanism is activated so as to produce forces acting in opposite directions between sections 4 and 5 after the locking means therebetween have been released.
  • the drawing shows a counterweight 11 positioned on the platform on that side of the hinge-axes remote from the mast, in order to balance the weight of same.
  • FIGURE 4 shows a preferred embodiment of the force generating mechanism for producing mutual telescoping of the two mast sections.
  • This mechanism includes a hydraulic jack of which one part, the cylinder 12 for example, is fixedly mounted axially at the outer end of outer section 4, for instance on a frame 13 rigid with section 4.
  • the rod 16 of jack 12 has its free end pivotally connected to a cross-member 17 adapted to bear against and lock onto the end of inner mast section 5a.
  • the jack is not under pressure and retracted, in the position shown in FIGURE 1.
  • the force it exerts on outer mast section 4 in the direction of arrow f, as it reacts against crossmember 17, inner section 5 and hinge point 6, causes erection of the mast into the vertical position, as explained precedingly.
  • the head of outer section 4 housing jack 12 forms a pivot 14 on which is rotatable a crane jib support 15, as is common practice in the crane building art.
  • the jib may be folded along base 4 when same is in its stowed transport position and can be moved into its operative position after the mast has been erected by means of suitable reeving means, well-known per se, which call for no description since they fall outside the scope of the present invention.
  • FIGURE 5 shows an alternative embodiment in which mast section 4, which is pivotally connected to rods 8, is the inner instead of the outer section, the outer mast section being accordingly hingedly connected to the platform as at 6.
  • FIGURE 5 also shows an alternative way of devising the force generating mechanism between the two telescoping sections, which mechanism consists in this case of a gearwheel 20 carried on i one of the mast sections and meshingwith a rack 21 car ried on the other section, gearwheel 20 being driven by a suitable motor (not shown).
  • the mast could be extended by means of a mechanism external thereto, such as a winch 22 pulling a rope 23 fastened to outer section 4 and running over an intermediate pulley 24.
  • a hoisting appliance having a mast transportable in a reclining position on a platform
  • the combination comprising two mutually telescoping sections forming part of said mast, an articulation about a horizontal axis be tween one side of one of said telescoping sections and the platform, linkage means with two hinge points about horizontal axes parallel to said horizontal axis, one of said hinge points connecting said linkage means to the other telescoping section on a side thereof remote from that side of the first mentioned section which is articulated on said platform and the other hinge point interconnecting said linkage means with said platform in spaced relationship with the articulation point of said first section, said first mentioned hinge point, in the reclining position of said mast, lying above and between the hinged connection point of said linkage means to said platform and the hinged connection point of the other telescoping section to said platform, whereby bodily pivotal motion of said two telescoping sections about said articulation is accompanied by a translation motion of said two sections relatively to each other.

Landscapes

  • Engineering & Computer Science (AREA)
  • Architecture (AREA)
  • Structural Engineering (AREA)
  • Civil Engineering (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Jib Cranes (AREA)

Description

June 18, 1968 P. DURAND 3,338,310
DEVICE FOR EXTENDING AND FOLDING BACK MASTS OR TOWERS APPLICABLE TO CRANES AND THE LIKE Filed Feb. 20, 1967 2 Sheets-Sheet 1 June 18, 1968 P. DURAND 3,388,810
DEVICE FOR EXTENDING AND FOLDING BACK MASTS OR 7 TOWERS APPLICABLE TO CRANES AND THE LIKE Filed Feb. 20, .1967 2 Sheets-Sheet 2 United States Patent 3,388,810 DEVICE FOR EXTENDING AND FOLDING BACK MASTS 0R TOWERS APPLICABLE TO CRANES AND THE LIKE Pierre Durand, Lyon, Rhone, France, assignor to Richier, Paris, France, a company of France Filed Feb. 20, 1967, Ser. No. 617,266 Claims priority, applicsation France, Feb. 24, 1966,
3 Claims. 3:1. 212-46) ABSTRACT OF THE DISCLOSURE A hoisting appliance having an erectable mast transported reclining on a platform and made of two telescoped sections, one of which has one of its sides pivotally connected to the platform about a horizontal axis, while the other has its opposite side pivotally connected to the end of a link member hingedly connected to the platform, whereby bodily pivoting the telescoped sections about the hinge axis of the first section on the platform causes translation of the two sections relatively to each other.
Background of the invention Summary of the invention In accordance with this invention, the mast or jib consists of two telescoped sections, of which one has one side pivotally connected to the erecting platform about a horizontal axis, while the other has its side remote from the aforementioned side pivotally connected to the end of a link member hingedly connected to the platform about a horizontal axis, whereby a motion of the two telescoped sections relatively to each other, resulting from a force exerted between the two sections, will, depending on the direction in which the force is exerted, cause either the folded reclining mast to be moved into the vertical extended position, or conversely the vertically extended mast to be moved into its retracted horizontal position.
Brief description of the drawing FIGURES 1, 2 and 3 are side elevation views of an embodiment of the invention as applied to a building crane, showing three different operative positions thereof;
FIGURE 4 shows an embodiment of control means utilizing a central jack, and
FIGURE 5 shows an alternative form of embodiment.
Description of the preferred embodiments Reference to the drawing shows a building crane the mast of which comprises a base 1 attached to a platform 2, on which said base is either reclining for transport as shown in FIGURE 1, or erected in the vertical position for operation of the crane as shown in FIGURE 3. Platform 2 is fitted with wheels 3 to enable it to be moved, and also with bracing means (not shown) such as jack means to immobilize it on a chosen location.
The base 1 is made up of two sections 4 and 5 placed one within the other and devised for mutual telescoping movement. By way of example, guide wheels (not shown) could be carried by the inner section 5 and roll on guideways on the outer section 4. In the example shown in the drawing, the sections 4 and 5 are assumed to be of square or rectangular cross-section but could obviously have any convenient cross-sectional shape.
Sections 4 and 5 are further assumed to be lattice sections, as is customary in crane mast on jib construction.
Inner section 5 is pivotally connected to platform 2 about a horizontal axis b along that of its edges perpendicular to the longitudinal axis of platform 2 which is applied against the latter when the base is reclining (FIG- URE 1), while outer section 4 has its opposite side pivotally connected about an axis 7 to the end of two links 8 positioned symmetrically with respect to the longitudinal centerline of platform 2. These links, which merge together on the drawing (but which could be replaced by a frame) are hingedly connected to platform 2 about a horizontal axis 9. The hinge axes 6 and 9 on platform 2 are sufficiently spaced for inner mast section 5 to be able to come to bear against the platform between these axes when it is in the erected position shown in FIGURE 3.
A force generating mechanism such as a hydraulic jack, screw jack, reeving system, rack device, or the like, acting on one hand against outer section 4 and on the other against inner section 5, enables opposed forces to be exerted thereagainst which are effective in moving the mast either from its reclining position shown in FIGURE 1 to its vertical position shown in FIGURE 3, or vice versa.
This. mechanism, a specific form of embodiment of which will be described hereinafter, may be positioned in the interval between sections 4 and 5, or centrally, or entirely external to sections 4 and 5, its location being such that the direction of the force it exerts passes above axis 6 whereby to produce a rotating moment thereabout.
The principle of operation of the device hereinbefore described will be readily understood.
If, starting from the position in FIGURE 1, the force generating mechanism is activated so that the force it exerts on outer section 4 is directed along arrow f, with the reaction taking place against section 5, then the moment which is generated as mentioned above on section 4 hinged about axis 6 will initiate pivotal motion of the assembly about axis 6 and a reaction of links 8 against telescoped section 4. The hinge points 7 of links 8 on section 4- then describe circular arcs having their centre at 9, whereby section 4 is pulled along inner section 5 and telescopes over the same, with the overall result that the mast gradually pivots about axis 6 and at the same time extends itself. In so doing it moves from the position in FIGURE 1 to the position in FIGURE 2, and ultimately to that in FIGURE 3. Obviously, this motion tends to be self-sustaining as soon as the centre of gravity of the mast moves past the vertical plane through axis 6. For this reason it is preferable for the force generating mechanism connected between sections 4 and 5 to be of the positive type, i.e. a jack or rack mechanism rather than a reeving system, in order to avoid uncontrolled terminal motion and ensuing shock loadings as the inner section 5 of the mast base contacts platform 2.
As FIGURE 1 clearly shows, outer telescoping section 4 is formed with a bevelled end 10 which is pivotally connected to the links 8. As the figure shows, this ensures that this end is always located above and behind hinge axis 6 and does not therefore hinder initiation of the pivotal motion; further the hinge points 7 are located above and between axes 6 and 9, which is preferable for eificient operation.
Obviously, locking means may be provided in order to unite sections 4 and 5 after the mast has been erected into the position in FIGURE 3.
In order to retract the mast and fetch it into its reclining position on the platform, the force generating mechanism is activated so as to produce forces acting in opposite directions between sections 4 and 5 after the locking means therebetween have been released.
The drawing shows a counterweight 11 positioned on the platform on that side of the hinge-axes remote from the mast, in order to balance the weight of same.
FIGURE 4 shows a preferred embodiment of the force generating mechanism for producing mutual telescoping of the two mast sections. This mechanism includes a hydraulic jack of which one part, the cylinder 12 for example, is fixedly mounted axially at the outer end of outer section 4, for instance on a frame 13 rigid with section 4. The rod 16 of jack 12 has its free end pivotally connected to a cross-member 17 adapted to bear against and lock onto the end of inner mast section 5a.
Initially the jack is not under pressure and retracted, in the position shown in FIGURE 1. When the jack is set under pressure, the force it exerts on outer mast section 4 in the direction of arrow f, as it reacts against crossmember 17, inner section 5 and hinge point 6, causes erection of the mast into the vertical position, as explained precedingly. In the illustrated example, the head of outer section 4 housing jack 12 forms a pivot 14 on which is rotatable a crane jib support 15, as is common practice in the crane building art. The jib, not shown, may be folded along base 4 when same is in its stowed transport position and can be moved into its operative position after the mast has been erected by means of suitable reeving means, well-known per se, which call for no description since they fall outside the scope of the present invention.
It goes without saying that the specific forms of embodiment described hereinabove are intended for exernplary purpose only and that changes and substitutions could be made therein without departing from the scope of the invention.
By way of example, FIGURE 5 shows an alternative embodiment in which mast section 4, which is pivotally connected to rods 8, is the inner instead of the outer section, the outer mast section being accordingly hingedly connected to the platform as at 6. FIGURE 5 also shows an alternative way of devising the force generating mechanism between the two telescoping sections, which mechanism consists in this case of a gearwheel 20 carried on i one of the mast sections and meshingwith a rack 21 car ried on the other section, gearwheel 20 being driven by a suitable motor (not shown).
In yet another alternative constructional form, the mast could be extended by means of a mechanism external thereto, such as a winch 22 pulling a rope 23 fastened to outer section 4 and running over an intermediate pulley 24.
I claim:
1. In a hoisting appliance having a mast transportable in a reclining position on a platform, the combination comprising two mutually telescoping sections forming part of said mast, an articulation about a horizontal axis be tween one side of one of said telescoping sections and the platform, linkage means with two hinge points about horizontal axes parallel to said horizontal axis, one of said hinge points connecting said linkage means to the other telescoping section on a side thereof remote from that side of the first mentioned section which is articulated on said platform and the other hinge point interconnecting said linkage means with said platform in spaced relationship with the articulation point of said first section, said first mentioned hinge point, in the reclining position of said mast, lying above and between the hinged connection point of said linkage means to said platform and the hinged connection point of the other telescoping section to said platform, whereby bodily pivotal motion of said two telescoping sections about said articulation is accompanied by a translation motion of said two sections relatively to each other.
2. A hoisting appliance as claimed in claim 1, wherein the telescoping section hingedly connected to said linkage means comprises a projecting portion carrying the hinged connection point to said linkage means.
3. A hoisting appliance as claimed in claim 2, wherein the telescoping section hingedly connected to said linkage means has its base disposed obliquely.
References Cited UNITED STATES PATENTS ANDRES H. NIELSEN, Primary Examiner.
US617266A 1966-02-24 1967-02-20 Device for extending and folding back masts or towers applicable to cranes and the like Expired - Lifetime US3388810A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FR50977A FR1482882A (en) 1966-02-24 1966-02-24 Device for straightening and folding masts or pylons, particularly applicable to cranes and lifting devices

Publications (1)

Publication Number Publication Date
US3388810A true US3388810A (en) 1968-06-18

Family

ID=8602207

Family Applications (1)

Application Number Title Priority Date Filing Date
US617266A Expired - Lifetime US3388810A (en) 1966-02-24 1967-02-20 Device for extending and folding back masts or towers applicable to cranes and the like

Country Status (6)

Country Link
US (1) US3388810A (en)
BE (1) BE694072A (en)
DE (1) DE1481809B2 (en)
FR (1) FR1482882A (en)
GB (1) GB1173523A (en)
NL (1) NL6702573A (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4598509A (en) * 1985-06-24 1986-07-08 Lee C. Moore Corporation Method and apparatus for raising and lowering a telescoping mast
US20100102017A1 (en) * 2007-02-16 2010-04-29 Itrec B.V. Hoisting crane and vessel with such a crane
US11613905B1 (en) * 2020-07-29 2023-03-28 Robert C. Lee Antenna tower construction/deconstruction stability assemblies and methods

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2370674A1 (en) * 1976-11-16 1978-06-09 Liebherr Werk Bischofshofen Crane with telescopic column - has extension by hydraulic jacks also able to swing column to horizontal position when not in use (SW 12.6.78)
DE2652212C2 (en) * 1976-11-16 1984-12-06 Liebherr-Werk Bischofshofen GmbH, Bischofshofen Crane with a device for erecting and telescoping its tower
DE4329715C1 (en) * 1993-09-03 1995-02-23 Dornier Gmbh Telescopic mast system
EP2025860A1 (en) * 2007-08-17 2009-02-18 BAUER Maschinen GmbH Deep drilling device and method for erecting a deep drilling device

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2548038A (en) * 1947-10-24 1951-04-10 Leona N Moliskey Fluid pressure actuated lifting apparatus
US3233375A (en) * 1961-02-14 1966-02-08 Richier Sa Vertically swinging extensible crane

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2548038A (en) * 1947-10-24 1951-04-10 Leona N Moliskey Fluid pressure actuated lifting apparatus
US3233375A (en) * 1961-02-14 1966-02-08 Richier Sa Vertically swinging extensible crane

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4598509A (en) * 1985-06-24 1986-07-08 Lee C. Moore Corporation Method and apparatus for raising and lowering a telescoping mast
US20100102017A1 (en) * 2007-02-16 2010-04-29 Itrec B.V. Hoisting crane and vessel with such a crane
US8459477B2 (en) * 2007-02-16 2013-06-11 Itrec B.V. Hoisting crane and vessel with such a crane
US11613905B1 (en) * 2020-07-29 2023-03-28 Robert C. Lee Antenna tower construction/deconstruction stability assemblies and methods

Also Published As

Publication number Publication date
DE1481809B2 (en) 1970-09-10
FR1482882A (en) 1967-06-02
DE1481809A1 (en) 1969-09-04
BE694072A (en) 1967-08-14
NL6702573A (en) 1967-08-25
GB1173523A (en) 1969-12-10

Similar Documents

Publication Publication Date Title
US4383616A (en) Luffing jib for construction crane
US3907066A (en) Wing-type scaffold system
US3804264A (en) Tower crane with rockable top sector
US3465899A (en) Telescoping boom for hydraulic crane
US3371801A (en) Extensible jib, mast or the like
US4546578A (en) Transportable holding assembly for rapid erection of buildings
US4134237A (en) Modular section mast
US3072215A (en) Folding personnel lift
US2772004A (en) Portable gantry crane
US4895263A (en) Foldable machine for handling and lifting loads
US3388810A (en) Device for extending and folding back masts or towers applicable to cranes and the like
US3045837A (en) Rotary tower crane
US4125193A (en) Climbing device for climbing crane
US4473214A (en) Luffing jib for construction crane
GB1218335A (en) Improvements in or relating to tower cranes
JPH0245274Y2 (en)
US3754666A (en) Folding crane
US4027441A (en) Arrangement for erecting and dismounting an elongate object having one end articulated to a foundation
US3084806A (en) Tower cranes
US3622013A (en) Extensible boom structure
US3378147A (en) Tower crane rotatable on its base
US3233375A (en) Vertically swinging extensible crane
US3357573A (en) Cranes
US3335876A (en) Collapsible tower crane
US3863407A (en) Telescopic crane jib