GB2252092A

GB2252092A - Gantry sling.

Info

Publication number: GB2252092A
Application number: GB9100245A
Authority: GB
Inventors: Thomas Stuart Parramore
Original assignee: Williams Fairey Engineering Ltd
Current assignee: WFEL Ltd
Priority date: 1991-01-07
Filing date: 1991-01-07
Publication date: 1992-07-29
Anticipated expiration: 2011-01-07
Also published as: GB9100245D0; GB2252092B

Abstract

A gantry sling arrangement for lifting a load (for example a military bridge module) by means of a crane has a cross- beam (10) having a pair of folding legs (20, 22) at the ends. The load to be lifted is positioned beneath the sling and is secured to pulley wheel blocks (48, 50). Each block carries a pulley wheel, around which a hoist rope (44, 46) passes. Each hoist rope is secured at one end (40, 42) to the cross-beam and at the other (56, 58) to a spreader bar (60) which has a hook (62) enabling the spreader bar to be lifted by means of a crane. The sling enables larger loads to be lifted than normal, for a given crane, with some of the load being transferred to the ground via the legs (20, 22). <IMAGE>

Description

GANTRY SLING The present invention relates to a gantry sling, and particularly though not exclusively to a sling which is suitable for use in the building of modular military bridges. The invention also relates to a method of building modular bridges.

When constructing a modular military bridge with crane assistance, the typical maximum loads that need to be lifted are those of the bridge modules which do not, typically, exceed about 4 tonnes. Each bridge module has to be lifted from a supply truck or the ground, and swung into position for connection onto the bridge.

During this operation, the crane is normally supported not by its wheels but by its stabilising outrigger jacks.

When the bridge has been constructed and launched across the gap to be spanned, there then remains the problem of lifting the home bank end of the bridge to remove the support on which it rests (a trestle or a building frame), and then lowering the end of the bridge to the ground. The lift required to raise the end of the bridge will, of course, be approximately half the total bridge weight; so, for an 8 module bridge weighing 4 tonnes per module, the lift required will be 16 tonnes. Although this static lift is at a much smaller outreach than is likely to have been required for the lift of the individual modules, its magnitude invariably determines the size of the crane required. As a consequence, the bridge construction is hampered by the use of a heavier and slower crane than is actually required for assembly of the various components.The use of winches rather than cranes for the construction of modular military -bridges would be possible but undesirable. Additional expensive equipment would be required, and the general view has been that modular bridges are best built with cranes, these cranes being available in any case as part of the standard military bridging kit.

The object of the present invention is to provide a means of increasing the static lift capacity of a crane at a specified outreach.

It will be appreciated from the following description that although this invention arose from a problem common to most military bridge construction, it could find much wider use in the construction and mechanical handling fields. In particular, it could be of use in situations where an infrequent, heavy crane lift is required, and where the provision of larger cranes is either impossible due to space limitations, or is not justified for cost or other reasons. For instance, it could be used to provide a means of lifting an ISO container on and off trucks which were operating away from their base without proper handling equipment such as cranes or large fork-lift trucks being available.

According to the present invention there is provided a gantry sling arranged to straddle a load to be lifted, a movable pulley wheel block having means for attachment to the load, and at least one hoist rope secured at one end to the sling and passing round a pulley wheel on the block by which the load can be lifted by a crane.

The sling preferably comprises a cross-beam having legs at either end thereof, the legs being arranged to straddle the load to be lifted, in use. So that the sling can conveniently transported, the legs may be hinged to the cross-beam, so that they can be moved from an extended, use position to a stowage position in which they lie substantially parallel to the beam. The legs could be lockable in the extended position and/or the storage position by means of locking pins.

Alternatively, the legs could be entirely removable from the beam.

In a convenient arrangement, the cross-beam may comprise first and second spaced generally parallel support beams, with the free end of the hoist rope being arranged to pass through the resultant gap in use. The attachment point of the other the end of the hoist rope to the sling may then conveniently be between the two beams, for example by means of a small transverse bar or pin extending across the gap.

The point of securement of the hoist rope to the sling, and the relative position of the pulley wheel block with respect to the sling itself may be so arranged that, when the free end of the hoist rope is raised without any load on the pulley wheel block, the block abuts a stop on the sling so that the entire gantry sling can be lifted. For example, the pulley wheel block may simply abut the lower side of the cross-beam.

Stowage means may be provided whereby the hoist rope may be safely stored when not in use. The free end of the rope may, for example, be pinned to a point on the cross-beam, with arcuate guide means being provided to ensure that the intermediate part of the rope is not left slack.

In one particular embodiment, there are two hoist ropes and two corresponding pulley wheel blocks and means for attachment to the load. With this arrangement, the free ends of the two hoist ropes may be secured to a spreader bar, the spreader bar being arranged to be lifted by a crane. Of course, more hoist or fewer ropes and pulley wheel blocks could be provided should it be considered desirable.

In an alternative embodiment, there may be means for synchronising the movement of two or more pulley wheel blocks, for example to prevent one block becoming lower than another if the load to be lifted is not constrained against rotation. To that end, there may be guide means for the hoist ropes so that the ropes are parallel and close together as they extend above the gantry sling. The ropes may then be secured together at the free ends or otherwise lifted at substantially a single point. In the preferred arrangement, the gantry sling has a cross beam comprising first and second spaced generally parallel support beams, and the guide means for each of the hoist ropes comprises first and second rollers mounted between these beams.Each guide rope may for example pass from its pulley wheel block, over a first roller, and under a second roller before extending upwardly for securement to a crane hook. Where there are two hoist ropes, the rollers under which the hoist ropes pass are preferably spaced relatively close to each other.

Where the gantry sling comprises a cross-beam and at least a pair of hinged legs, the legs can each be comprised of two uprights with a gap therebetween so that when the legs are folded up adjacent the gantry sling, the pulley wheel block or blocks are then trapped between the legs and the cross-beam. The means for attachment to the load, on the pulley wheel blocks (for example load hooks) may then extend into the gap between the leg uprights. At the other side, the block or blocks may abut the cross-beam.

If an additional mechanical advantage is required, the or each hoist rope may be reeved over more than one pulley wheel block. By choosing the number of pulley wheel blocks over which the hoist rope passes before it is secured to the sling itself, one can arrange for various load multiplications.

Depending upon the circumstances, one or more pulley wheel blocks maybe provided. That part of the guide rope which extends between the pulley wheel block and for example a crane lifting hook may be restrained by guide means against sideways movement. These guide means could for example comprise first and second restraining guide rollers, one on each side of the hoist rope, which extend between the parallel support beams of the cross beam.

The present invention also extends to a method of using a crane to lift a load by means of a gantry sling as previously described.

According to a second aspect of the invention a method of lifting a load comprises straddling the load with a gantry sling, attaching a pulley wheel block to the load and a first end of a hoist rope to a crane, the hoist rope passing around a pulley wheel on the block and being secured at its other end to the gantry sling, and raising the first end of the hoist rope with the crane.

According to a third aspect of the invention a method of building a modular bridge includes the steps of straddling a module of the bridge to be built with a gantry sling, attaching a pulley wheel block to the module and a first end of a hoist rope to a crane, the hoist rope passing around a pulley wheel on the block and being secured at its other end to the gantry sling, and raising the first end of the hoist rope with the crane to lift the module.

The term "rope", as used in this specification, is not to be interpreted strictly. It is intended to encompass, along with-a conventional ropes, other types of flexible elongate means which could be used in place of conventional ropes, including but not limited to cords, chains, wires, metal lines and so on.

The invention may be carried into practice in a number of ways and one specific gantry sling will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a gantry sling embodying the present invention; Figure 2 is an end view of the gantry sling of figure 1; Figure 3 shows the gantry sling of figure 1 in its folded position; Figure 4 shows an alternative gantry sling having only a single hook; Figure 5 is an end view of the gantry sling of Figure 4; Figure 6 shows another alternative gantry sling having multiple sheaves; Figure 7 is an end view of the gantry sling of Figure 6; Figure 8 shows yet another alternative gantry sling, for lifting rotatable loads; Figure 9 is an end view of the gantry sling of Figure 8.

The gantry sling shown in figures 1 to 3 has a cross-beam 10 consisting of two rigid end pieces 12, 14, extending between which there are two parallel spaced support beams 16, 18. A pair of parallel folding legs 20, 22 are hinged at pivot points 24, 26 to the respective end pieces 12, 14, so that the legs may be moved between an extended position as shown in figure 1, and a storage position shown in figure 3. In the extended position the legs are locked in place by pins 28, 30 inserted into corner brackets of the end pieces 12, 14.

As can best be seen in figure 2, the leg 22 consists of apair of uprights 32, 34 connected together at the lower ends by a base or foot 36. The construction of the leg 20 is similar, this leg having a foot which is indicated in figure 1 by the numeral 38. As will be appreciated, the feet 36, 38 should have sufficient transverse extent to ensure that the gantry can stand on the ground without tending to topple over sideways.

The stability could be improved, if desired, by increasing the width of the feet, 36, 38, and/or positioning the upright 32, 34 of the leg 22 and the corresponding uprights of the leg 20 at an angle to each other. Each of the four uprights could then rest on its own individual foot (not shown).

The cross-beam 10 carries anchorage points 40, 42 for twin hoist ropes 44, 46. These are reeved around respective pulley sheaves (pulley wheel blocks) 48, 50 carrying lifting hooks, 52, 54. The free ends of the hoist ropes 44, 46 are releasably connected at further anchorage points 56, 58 to a spreader bar 60 which can itself be connected at its centre via a lifting ring 62 to a lifting crane hook (not shown).

When the gantry sling is hanging unloaded from a crane, the sheaves 48, 50 will abut the underside of the support beams 16, 18, without damage. When the sling is lowered to the ground, the sheave blocks will go free and can be gradually lowered downwards until the lifting hooks 52, 54 can be connected to the load (not shown).

When lifting commences, the gantry, straddling the load, will react on the ground, this reaction taking at least some of the weight that would otherwise have to be borne by the crane. In the arrangement shown in the drawings, approximately half the weight would be reacted on the ground, and the remainder at the crane hook. In practice, of course, the mechanical advantage will be rather less than the velocity ratio, due to inefficiencies; so the crane load may be actually 10 or 15% greater than half the weight of the load which is being lifted. Once the load is connected and is being lifted, the transverse stability of the gantry will be significantly increased due to the upward force which is being applied to the lifting ring 62.

Although the gantry sling shown in the figures is provided with twin sheaves on hooks, it could equally well be arranged with a single sheave, or with multiple sheaves. The lifting capacity could further be increased by additional reeving, for example 2, 3 or 4 times. It will be appreciated, however, that this would require a correspondingly higher lift from the crane which may prove impractical in many situations.

When the gantry sling is to be stowed, the pins 28, 30 are removed and the legs 20, 22 are folded up towards the cross-beam 10. The hoist ropes 44, 46 are uncoupled from their anchorages 56, 58 on the spreader bar 60, and are instead pinned to respective stowage points 64, 66 on the end pieces 14, 12. In their stowed positions, the hoist ropes 44, 46 pass around curved guides 68, 70 which extends between the support beams 16, 18, so ensuring that they do not simply hang loose during transport. The sheaves 48, 50 are trapped between the cross-beam 10 and the legs 20, 22. The spreader bar 60 is stowed separately.

It is of course not essential to the present invention that exactly two hooks are provided, and one, three or any greater number could be envisages. Figures 4 and 5 show an alternative gantry sling in which there is only a single hook. In addition, there are a number of other minor changes from the gantry sling shown in Figures 1-3. In particular, the lifting rope is now restrained from lateral movement by first and second restraining rollers 100, 102. The folding legs 104, 106 each now have a greater spread, to improve stability, and each has cross struts 108 for increased strength. It will be appreciated that any or all of these changes could also be incorporated into the embodiment of Figures 1-3.

Figures 6 and 7 show a further alternative embodiment in which additional reeving is provided to increase the mechanical advantage.

Yet another alternative embodiment is shown in Figures 8 and 9, this being designed to ensure that the two lifting hooks 110, 112 always move together as lifting proceeds. In comparison with the gantry sling of Figure 1, this embodiment includes four additional rollers 114, 116, 118, 120. The left hand lifting rope passes over roller 114 and under roller 116, while the right hand lifting rope passes over roller 120 and under roller 118. Both lifting ropes are then secured to a single lifting hook 122, and the spreader bar 60 of Figure 1 is dispensed with.

When the gantry sling of Figure 1 is used to lift a load which is not constrained against rotation about an axis perpendicular to the plane of the paper, the spreader bar 60 is likely to tilt, and one lifting hook will then be higher than the other. With the embodiment of Figures 8 and 9, this rotation is impossible as both hooks 110, 112 are constrained to move at the same rate.

Claims

CLAIMS:

1. A gantry sling arrangement including a gantry sling for straddling a load to be lifted, a movable pulley wheel block having means for attachment to the load, and a hoist rope secured at one end to the sling and passing round a pulley wheel on the block by which the load can be lifted by a crane.

2. A gantry sling arrangement in which the sling comprises a cross-beam having legs at each end thereof, the legs being arranged to straddle the load to be lifted.

3. A gantry sling arrangement as claimed in claim 2 in which the legs are hinged to the cross-beam.

4. A gantry sling arrangement as claimed in claim 3 in which the legs are movable from a use position to a stowage in which they lie substantially parallel to the beam.

5. A gantry sling arrangement as claimed in any one of claims 2 to 4 in which the cross-beam comprises first and second generally parallel support beams between which the hoist rope passed in use.

6. A gantry sling arrangement as claimed in claim 5 in which the hoist rope is secured to the sling at a bar or pin which extends between the first and second support beams.

7. A gantry sling arrangement as claimed in any one of the preceding claims in which the point of securement of the hoist rope to the sling, and the relative position of the pulley wheel block with respect to the sling are so arranged that, when the free end of the hoist rope is raised without any load on the pulley wheel block, the block abuts a stop on the sling so that the entire sling is lifted.

8. A gantry sling arrangement as claimed in any one of the preceding claims in which there are two hoist ropes and two corresponding pulley wheel blocks and means for attachment to the load.

9. A gantry sling arrangement as claimed in claim 8 in which the two hoist ropes are secured to a spreader bar, the spreader bar being arranged to be lifted by a crane.

10. A gantry sling arrangement as claimed in claim 8 or claim 9 including means for synchronising the movement of the two pulley wheel blocks as the load is being lifted.

11. A gantry sling arrangement as claimed in claim 10 in which the means for synchronising the movement of the two pulley wheel blocks includes guide means for the hoist ropes so that the ropes are parallel and close together where they extend above the gantry sling.

12. A gantry sling arrangement as claimed in claim 11 when dependent upon claim 5 or claim 6 in which the guide means comprise respective rollers for the ropes, mounted between the first and second support beams.

13. A gantry sling arrangement as claimed in any one of the preceding claims including guide means on the sling through which that part of the or each rope on the far side of the pulley wheel from the point of attachment to the sling passes.

14. A gantry sling arrangement as claimed in claim 4 in which the legs each comprise two uprights with a gap therebetween so that when the legs are folded up adjacent the cross-beam, the pulley wheel block is then trapped between the legs and the cross-beam.

15. A gantry sling arrangement substantially as specifically described with reference to figures 1 to 3, or with reference to figures 4 and 5, or with reference to figures 6 and 7, or with reference to figures 8 and 9.

16. A method of lifting a load comprising straddling the load with a gantry sling, attaching a pulley wheel block to the load and a first end of a hoist rope to a crane, the hoist rope passing around a pulley wheel on the block and being secured at its other end to the gantry sling, and raising the first end of the hoist rope with the crane.

17. A method of building a modular bridge including the steps of straddling a module of the bridge to be built with a gantry sling, attaching a pulley wheel block to the module and a first end of a hoist rope to a crane, the hoist rope passing around a pulley wheel on the block and being secured at its other end to the gantry sling, and raising the first end of the hoist rope with the crane to lift the module.

18. A method of lifting a load substantially as specifically described with reference to the drawings.

19. A method of building a modular bridge substantially as specifically described with reference to the drawings.