Offshore Structure Loads and Strength - Offshore Structures: Design, Construction and Maintenance - page 38

Most classification societies with jurisdiction in the U.K. sector of the North
Sea have classification notes available that include helideck specifications.
Because the main duties of some of these authorities is primarily classification
of floating structures, the helideck specifications generally appear only within
rules for mobile offshore units and the like. Two, however, Lloyd s Register

of Shipping (LRS) and Det Norske Veritas (DNV), have adopted identical
specifications for fixed platforms.
Tables 2.12 and 2.13 summarize the loading requirements for most regular
specifications. Table 2.12 is concerned with the load specifications during
helicopter landings, while Table 2.13 relates to helicopters in the stowed position.
From both tables, it can be seen requirements vary considerably among the
specifications, with particular variation in:

'

The factor on MTOW (M) for emergency landing conditions. ●

Whether a deck response factor is considered.

●

Whether the level of superimposed load is considered simultaneously or
separately.

●

Whether a lateral load is considered simultaneously with the emergency
landing load.

●

Example of Helicopter Load
The helicopter loads presented in Table 2.12 areusedherefortheskid
loading model. In the SACS input loading menu for a Bell-212 helicopter,
the MTOW= 50 kN (5 tons).
The helicopter has two skids. Each skid

' s geometrical dimensions are

2.856 (W) meters, with the center of gravity (C.o.G.)
point of application at the middle of the skid. The height of the helicopter
fuselage is taken as 2 m.
1. CAP-437 imposed live load = 0.5 kN/m 2
2. At-rest condition = 1

assumed to be 3.68 (L) ×

MTOW = 50.0 kN
3. Normal operating condition = 1.5

×

× 1.3 × MTOW = 97.50 kN

4. Emergency landing condition = 2.5 × 1.3 × MTOW = 162.50 kN

The landing conditions, either normal operating or emergency, are combined
with lateral horizontal force = 0.5 × MTOW= 25.0 kN applied on both skids.

2.2.6 Crane Support Structures
The crane support structures comprise the crane pedestal and its connections to
the topside structure

s primary steelwork. They do not include the slew ring or
its equivalent or the connections between the slew ring and the pedestal.
Crane support structures should, where practical, be attached at the intersec-
tion of topside primary trusses and connected at main deck elevations with
minimal eccentricities.

'