CRANE MATS Ӏ SECTOR SPOTLIGHT
SUPPORT SYSTEMS
Crane mats and outrigger pads may seem simple but neglect them at your peril, says Julian Champkin.
There are few more distressing sights than a mobile crane on its side in the mud. A hugely expensive piece of kit, crammed with cutting-edge tech, out of action and rendered redundant by something as simple as soft ground that was unable to support the crane safely. That is the best-case scenario; worst case – people get injured or killed. Ground collapse from
inadequately rigged mobile cranes is one of the leading causes of cranes overturning. Figures from crane manufacturer Tadano (looking at 174 crane accidents
Tadano’s
Ground Collapse Prevention system uses crane self- weight and sensors
in Japan between 1989 and 1994) say that ground collapse accounts for approximately 39% of incidents. Traditionally, preventing such occurrences has relied heavily on the operator’s ability to judge soil conditions and to react intuitively – a skill that can vary significantly based on experience. Nowadays more systematic and reliable solutions are available. There are two obvious parts to stopping a crane from subsiding into the earth. First, what is the ground pressure that the crane and its load are going to exert on the surface it is standing on? Second, is
the ground it is standing on strong enough to support that pressure? The first is easy enough to
calculate. All it really needs is data which is (or should be) easy to find. The second is not so certain… For that first requirement, the
ground pressure exerted by the crane, the crane manufacturer knows the weight of the crane, while the crane user knows (or should know!) the weight of the load. That load will be distributed among several outriggers in proportions that will vary according to such factors as the weight of the load, the crane’s reach, and the position of the boom. The crane manufacture supplies this data, perhaps electronically, in the form of load charts. Crane manufacturer Liebherr,
for example, has an app, called CP Mobile, which covers all of its machines from 2002 onwards and includes all load charts in the field. After selecting the appropriate crane and the respective load, ground pressure calculations can be carried out quickly and easily, the company says.
GROUND STRENGTH The second requirement, the strength of the ground, is more complex. The earth and soil that we stand on has, in general, been deposited by the forces of
16 CRANES TODAY
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