Safely does it12 April 2001
Chartered engineer Gordon Stewart describes procedures for tower crane erection and demobilisation in Australia
This article is written with the aid of work previously carried out by the writer and John Holland Constructions Pty Ltd, which owns and uses Raimondi electric tower cranes in Australia; also Sutville Pty Ltd, owner and hirer of Australia’s largest fleet of modern Favelle Favco diesel/hydraulic luffing cranes.
Our procedures do not guarantee a non-accident condition but do go a long way to minimising events which may make the crane unserviceable due to damage in erection, use or dismantling. The planning starts with the locating of the crane before erection. The location must ensure that on completion the crane can be correctly brought to the ground with the available equipment such as a mobile crane, allowing room for outriggers to be extended. This is just as important a function as being able to construct with the crane.
The location of the crane must also ensure that soil bearing capacity for the footing is available and that such footings – piles, block, rock bolts, steel grilles – can support the structure. The required bearing loads will often be determined by out of service wind conditions for a luffing crane. Australia has minimum wind standards of 43m/s for a one-year erection time and significantly greater in those areas subject to cyclonic periods. It may then become apparent that it will be necessary to specifically consider free-standing heights both in and out of service and during erection and dismantling. Clearly the most desirable erection is for boom weather vaning conditions, but often construction sites are tight and vaning is not an option. If the erection and dismantling conditions are critical, in the eyes of the design engineer, these need to be highlighted from initial involvement in a documented format.
A general erection and dismantling procedure should be a written document in the format of a job safety audit (JSA) and this should include whose responsibility it is to supply:
• crane and rigging crew
• support crane crew
• fitters and technicians
• professional engineering
• co-ordination of operation
• construction site responsibilities.
From this initial list it is appropriate that each contractor should detail its list to a much greater degree and all documents exchanged with each party and then discussed at a toolbox meeting. If the crane and rigging crew only carry out crane and rigging work and it always works with the same fitters and professional engineer, then a consistent procedure will be in place. Often people change and minor changes can lead to disaster if all are not adequately briefed.
The professional engineer should have the responsibility of ensuring that the rigging crew is aware of the crane manufacturer’s directives for work on its crane. These should include the order of addition or removal of components (not only the counterweight). Clearly they should be aware of slewing during crane support on the climbing frame and the extent to which a load can be luffed under the same condition.
Crane components for assembly should be of known weight. These may be available from the crane operator manual but until crews are comfortable with the items it may be necessary to use the mobile crane’s load moment indicator to check actual weights. These should be recorded in an appropriate location for future reference.
Most crane manufacturers recommend tower bolt torques to be applied. The engineer should make sure that a new crew of fitters to a crane erection is aware of this item and he should inspect the checking of torque, if he feels it necessary An electric crane is more difficult to check in the storage yard than a diesel crane and some specific checking should be carried out before disassembly. We have therefore used a suitably qualified electrical/ mechanical engineer to run through all electronic and mechanical functions, including a test lift of a certified load. The work has a written detailed report, which is added to the crane logbook.
If tower bolts are used (sometimes shear pins substitute) a record is kept of their location and before re-use these bolts are magnetic particle crack tested, initially 10% and if no faults are found the others are assumed to be crack free.
When the crane is returned to the yard tower sections are visually inspected for cracks, dents, buckling and corrosion, as is the boom and A frame. The winch brakes are dismantled and inspected and relined if required. Hoist ropes are normally removed from the drum before the crane is lowered from erection. During winding to the spool the rope is visually inspected, greased and tagged with its length. Rope test certificates from a test break are filed and the history of the rope’s use recorded. In Australia cranes can be erected for buildings from five or six floors up to 80 floors and clearly the ropes are fitted to suit the required building heights. Long ropes are not used on short jobs.
An overall view of our mode of operation is to keep the integrity of the crane intact and to minimise down time at construction sites from crane breakdowns.
Duties of the crane driver include daily checks and greasing at points described in the JSA, which is applicable to his function. A driver’s logbook, completed daily, is kept at ground level and ensures that ‘management’ can assess particular items for service that may not be included in the manufacturer’s manual.
It is our general opinion that very few crane accidents occur in Australia from inadequate crane design but many occur from inadequate control of the crane by management in the broadest sense; or through driver error; or from a lack of understanding by the driver, which might be summed up as driver training.