Mobile Crane Ground Bearing Pressure
Mobile crane ground bearing pressure is the vertical pressure a crane imposes on the supporting surface through its wheels, tracks, outriggers, or stabilizers, including any mats or cribbing. It must not exceed the allowable ground bearing capacity to prevent ground failure and maintain crane stability. Calculated as force divided by effective contact area, it is critical for safe crane setup and operation.
On a manufacturing shop floor or yard, mobile crane ground bearing pressure must be assessed before setup to ensure the surface (concrete slab, gravel, asphalt) can support the crane and load. Pre-lift planning identifies maximum outrigger or track reactions from manufacturer data, calculates pressure using force/area, and compares it to site-specific allowable ground bearing pressure (AGBP). If pressure exceeds AGBP, operators increase mat size or cribbing, relocate the crane, or reduce load. WorkSafeBC requires blocking and cribbing sized to keep loads within bearing capacity. Documentation of calculations, ground capacity, and mat configurations is essential for compliance and safety.
How is maximum ground bearing pressure for a mobile crane typically determined?
Maximum ground bearing pressure is determined from crane manufacturer documentation (load charts, technical manuals) providing maximum outrigger loads, track pressures, or wheel loads for specific configurations. For non-standard lifts, engineering analysis calculates reactions including dynamic, wind, and tilt allowances. The pressure is calculated as support load divided by effective contact area, then compared to allowable ground bearing pressure with a safety factor (typically ≥2).
What is the difference between ultimate ground bearing capacity and allowable ground bearing pressure in crane setup?
Ultimate ground bearing capacity is the maximum pressure the ground can withstand before failure (shear, punching, global instability), determined by geotechnical analysis. Allowable ground bearing pressure (AGBP) is the ultimate capacity divided by a safety factor (commonly 2 for temporary crane loading). AGBP ensures actual ground bearing pressure, including uncertainties like soil variability and dynamic effects, remains within safe limits and is used directly in setup documentation.
How does WorkSafeBC expect employers to manage ground bearing pressure for mobile cranes?
WorkSafeBC OHS Regulation Part 14 requires mobile cranes to be used only on surfaces capable of safely supporting the equipment and load. Blocking, shoring, or cribbing must be sized to ensure support loads do not exceed bearing capacity. A qualified person (often a professional engineer) must determine ground bearing capacity, ensure crane support loads are below it with adequate safety margin, and retain documentation for due diligence and compliance.