Spider crane
Also called Mini crane, Tracked mini crane
A compact, tracked crane with narrow tracks and outrigger-supported legs, designed to access confined spaces such as building interiors or narrow side passages that conventional mobile cranes cannot reach. Despite their small size, spider cranes can impose significant point loads through their tracks or outriggers and often need matting on delicate floor finishes or soft ground.
In practice
The whole point of a spider crane is a small footprint, and that is exactly what raises the pressure under each foot. A machine light enough to go through a doorway still concentrates its weight, its counterweight and its load through four small pads — so the pressure it delivers can be comparable to plant many times its size, over an area small enough that whatever is underneath has no chance to share it.
Where this comes from: Site practice in confined-space lifting; the mismatch between machine size and foot pressure is what makes matting a routine requirement.
Where it matters on site
Indoors, the question is usually not the ground but the structure: a suspended slab, a raised floor, a mezzanine, a heritage surface. Those are point-load checks against someone’s structural capacity, and the answer has to come from whoever owns the building rather than from the crane. Spreading each foot onto a mat is what turns an impossible point load into a case that can be assessed.