However such operations often present various other problems. These include how to lift when there is no permanent facility, no access for a crane or mobile gantry, and where headroom may be restricted.
Typically this occurs when items such as pumps are located in pits, under overhangs or walkways and out of reach of a crane. With luck, the structure supporting the walkway will be strong enough to take the load, but its adequacy should always be checked by someone competent to do so. This is where some forethought can pay dividends. By looking in advance at where such items are located, estimating what they weigh and assessing what facility there is to lift and move them, potential lifting points can be identified, checked and marked accordingly for future use.
It is often the case that the strength is adequate but there isn’t a suitable structural element directly above the centre of gravity of the load. Furthermore, it is likely that the load will have to be travelled at least a short distance to where it can be landed onto a pallet or hand truck. Again it is unlikely that the structural element will run in the direction needed and so function as a runway beam.
One solution is to consider installing a temporary runway suspended from the overhead structure. It can be a traditional rolled beam section with a trolley running on the bottom flange, but this can take up precious headroom and may itself be a problem to lift and install. A lighter and easier to handle alternative is one of several brands of proprietary track sections where the trolley runs inside the track box minimising the headroom needed.
Another solution is to use two hand chain blocks suspended from two separate points of the overhead structure – each working at an angle to the vertical in a V formation, with the point of the V directly over the centre of gravity of the load. By hoisting on both in unison, the load can be lifted vertically. Then by lowering on one and hoisting on the other, the load will travel towards the block which is hoisting until it is hanging vertically below and the block lowering has lost all tension.
Contrary to the safe use information from most hand chain block manufacturers, this does involve using the blocks at an angle to the vertical. However the manufacturers cannot cover every possible application so generally take the cautious approach of limiting use to what they can be sure will be safe. With some sensible precautions, hand chain blocks will work entirely satisfactorily at the sort of angles required to perform this operation, typically not more than 30 degrees to the vertical. If that is not adequate to travel the load the full distance required, it can be done in stages with additional blocks suspended at appropriate intervals.
The precautions necessary for the blocks are to ensure that they are not overloaded, are free to align so as to operate in a straight line between top and bottom hooks and that the operative can be positioned to operate the hand chain at the correct angle. With regard to loading, each block should have a SWL equal to or in excess of the full load.
An alternative to hand chain blocks is lever hoists. When used inverted so the body climbs the chain, the lever can usually be kept within reach of the operative. However standard lever hoists generally have a relatively short chain so, depending upon the headroom, a sling may be required to connect the lever hoist to the supporting structure. The same precautions are required in respect of SWL and being free to align.
Another variation I have seen is to use one block or lever hoist coupled with a winch or some other means of pulling horizontally. It has the advantage that only one overhead lifting point is required and it is often easier to find a suitable anchor point in the right direction from which to exert the horizontal pull. However this is not a good method and, except when only very small angles to the vertical are involved, is best avoided.
The reason is that in the two block method, the load is shared and, within the limited range of angles, will never exceed the full load. In this method, one block takes all the load. When the chain is vertical it has 100% of the load but, as the angle to the vertical increases, the load on the block and the structure increases beyond 100%. Furthermore, if care is not taken and the sideways pull drops below the horizontal, that will add even more load to the block and structure.
In all cases there are also precautions to be taken with regard to the supporting structure. If it is to be loaded at an angle, then the checks already referred to should take account of the angle as well as the maximum load. There is also the question of how the connection is made to the supporting structure. The usual connection for a vertical lift is a girder clamp but many are not rated for angular loading. This is not just a matter of the loading on the clamp but, depending upon the beam section, it can also have a significant effect on the beam.
Old style RSJs had relatively thick tapered flanges, well suited to resisting flange bending arising from tip loading. Modern Universal Beam sections are produced in several weights. Whilst those of each nominal size all have the same dimensions of depth and width, the lighter weights have a thinner section. This has the advantage of making them relatively stiff for their weight but, coupled with very little flange taper, it reduces the ability of the flanges to resist bending. Therefore on such sections, a beam clamp which locates onto the flange tip is less efficient than one which locates nearer to the web and angular loading on the flange tips makes the situation worse.
Consider also how the supporting structure is loaded for its normal purpose. If it is something such as a walkway, it may be cantilevered in which case the bottom flange will be in compression. The compressive force will add to any loading which tends to bend the flange. If the flange collapses, it will no longer stiffen the web which will buckle and the cantilever will collapse. This is an extreme case but it is possible that a structure which is adequate for a properly applied vertical load can fail when the same load is badly applied at an angle.
A similar situation can arise by another frequently used method of making a temporary connection to a supporting structure, that of simply wrapping a sling around the section. In this case the sling acts on the tips of the top flange, tending to bend the flange downwards. If the structure is loaded as a beam, the top flange will be in compression and, as in the previous example, the compressive force will add to that tending to bend the flange. The result is the same. If the flange collapses, it will no longer stiffen the web which will buckle and the beam will collapse.
In the absence of a permanent lifting facility or adequate access for a temporary facility it is often necessary for the rigger to devise other ways of getting the job done. It may entail using equipment outside of the boundaries recommended by the manufacturer and lifting from structures primarily intended for other purposes. Both present potential problems but with adequate thought, planning and skill they can, in many cases, be overcome. The important points are to ensure that the equipment is loaded in the manner intended and that the structure is adequate bearing in mind the not just the weight of the load but also the method of handling and thereby the forces imposed on the structure, the line of those forces and the method of connecting to the structure. It may not be ideal but it may be the only viable way of getting the job done.
This article is intended to highlight the potential problems but also, I hope, to illustrate that, with care, it can be done safely.
About the author
Derrick Bailes is technical consultant (formerly chief executive) for the Lifting Equipment Engineers Association, 3 Osprey Court, Kingfisher Way, Hinchingbrooke Business Park, Huntingdon, PE29 6FN, tel: +44 (0)1480 432 801, fax: +44 (0)1480 436 314, email: info@leea.co.uk.
