.
Structural response factor for supporting structure
.
Area load
.
Horizontal force as proportion of landing gear collapse load.
Permanent Loads
. Self weight of structure and fixed appurtenances.
Environmental Loads
.
Wind, snow and ice, etc.
.
Inertial loads.
9.6.3 Normal Operations and Helicopters at Rest Variable Loads:
.
Helicopter static loads (local patch loads on landing gear)
.
Area load
.
Helicopter tie down loads, including wind loads from a secured helicopter.
Permanent Loads:
. Self weight of structure and fixed appurtenances.
Environmental Loads:
.
Wind, snow and ice, etc
.
Inertia loads.
9.6.4 Design Loadings
The designer should consider the following design loadings within the load combinations described above for a fixed or floating offshore installation.
9.6.4.1 Helicopter Landing Gear Collapse Loads
The maximum dynamic loads from an emergency landing may be determined from the collapse loading of the landing gear. This should be obtained from the helicopter manufacturer.
Alternatively, default values may be used for design by considering an appropriate distribution of the total impact load.
A single main rotor helicopter may be assumed to land simultaneously on its two main undercarriages or skids. Local patch loads should be used in design corresponding to the configuration of the landing gear.
The design landing load is the landing gear load based on a percentage of the helicopter's gross weight. The recommended percentage and helicopter gross weight should again be obtained from the helicopter operator or helicopter manufacturers supplied data. See also Appendices 4 to 13.
9.6.4.2 Structural Response Factor
The dynamic load determined as above should be increased by a factor for the structural response of the helideck. This factor will depend on the natural frequency of the deck structure. Unless values based upon particular undercarriage behaviour and deck frequency are available, a minimum structural response factor should be used.
9.6.4.3 Imposed Area Load
To allow for personnel and cargo transfer and snow and ice (in locations where these are possible) for minor equipment left on the helideck, etc, a general area load should be included. The imposed load is uniformly distributed over the entire safe landing area including any solid safety shelves.
9.6.4.4 Horizontal Forces
A concentrated horizontal imposed action as a proportion of the MTOW of the helicopter, shall be applied at the main landing gear locations and distributed in proportion to their vertical loading. This shall be applied at deck level in a direction to produce the most severe loading conditions for the elements considered.
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