Offshore cranes rotate on pedestals. API 2C requires that pedestals have unusually high strength
requirements to ensure the crane does not overturn or easily separate from the pedestal.
The top portion of the pedestal attaches to the crane and is usually provided by the crane manufacurer.
The top portion of the pedestal is often field-welded to the lower portion.
The lower portion of the pedestal connects the crane pedestal to the supporting base (platform, vessel, etcetera). The connecting structure between the crane pedestal and the crane base is the responsibility of the purchaser and must be properly engineered.
Crane manufacturers must provide detailed crane pedestal reactions. This is the loading that the crane will impart upon the crane support. The reactions include load factors SWLH*Cv*PF. Three forces and three moments may be provided at each radius. API 2C 7th ed. paragraph 6.2 requires that "Pedestals, kingposts, and other crane-support structure shall be designed for the loads defined in Section 5 with an additional factor, the pedestal load factor (PF), that applies to the vertical and horizontal loads due to the factored load". This means that for strength design, the crane pedestal and supporting structure must be designed for reactions induced by dead load (including effects of any crane accelerations), wind load, and a multiple-factored live load of SWLH*Cv*PF. These loads imparted by the crane on the supporting foundation are provided by the crane manufacturer.
Crane manufacturers must provide fatigue design loads in accordance with API 2C for on-board lifts. Fatigue reactions include reactions induced by 50% of SWLH. For fatigue design guidance of crane foundation, refer to a suitable design code such as API RP 2A.
There have been more than a few vessel crane foundation
failures due to:
(1) owners not having the crane foundation properly engineered, and
(2) designers using traditional vessel codes which may only account for SWL and dead loads, rather than SWLH*Cv*PF and dead loads.