Load spread
Also called Load spreading, Load distribution
The principle of distributing a concentrated load, such as an outrigger point load, over a larger ground area so the resulting bearing pressure is reduced to within the ground’s safe bearing capacity. Crane mats and outrigger pads work by load spread, and the degree achieved depends on a mat’s size, thickness and stiffness.
In practice
Load spread is a principle rather than a formula with one answer. How far a load actually spreads through a mat depends on the mat’s thickness and stiffness and on the ground underneath it, and the assumption used in a calculation — usually expressed as an angle taken through the mat — is a design decision. Your temporary works designer sets the figure that applies to your lift; a mat supplier cannot set it for you.
Where this comes from: Standard lift planning and temporary works practice. The spread a particular mat may be assumed to achieve is a design decision, not a property of the mat alone.
Where it matters on site
Two mats of the same plan area can spread very differently: a thin, flexible panel deflects and delivers much of the load close to the foot, while a stiffer build-up carries it further out towards its edges. That is why plan area alone is a poor way to compare mats, and why stiffness matters as much as strength when the failure being designed against is the ground giving way rather than the mat breaking.