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The design engineer should consider all likely design loads and load combinations.
As well as helicopter landing loads, the helideck has to be designed to cope with imposed loads on the deck from personnel, freight, refuelling and other temporary equipment, as well as environmental loads from wind, snow and ice, rotor downwash, etc, and its own self weight.
The design should also take account of wind turbulence and hot and cold gas thermal effects. Turbulent airflow across the landing area can be caused by wind flow around adjacent structures, including flare stacks and turbine exhausts (which can also cause temperature gradients). These effects can seriously influence helicopter landing and take-off performance characteristics.
Modelling methods such as wind tunnel testing or computational fluid dynamics computer modelling should be used to determine suitable limits, on helicopter operational weights and directions on take-off and landing, that may be necessary for certain wind directions and installation operating conditions – see Section 10.
The supporting structure, deck plate, stringers and supporting beams should be designed to resist the effects of local skid or wheel loads acting in combination with other loads in the most severe location for the element of structure being considered. Helicopters should be considered to land anywhere within the designated landing area and parked or stowed anywhere on the helideck.
Helideck loadings should be analysed to determine the distribution of forces and bending moments. The helicopter should be positioned to maximise the internal forces on the component being considered.
9.2 MAIN REFERENCES
The codes and standards applicable to the structural design of the helideck will be determined by where the helideck is to be operated and the national jurisdiction governing the installation or vessel of which the helideck will become part. As a general guide, the following design codes may apply:
.
ICAO Annex 14 Volume II Heliports
.
ICAO Heliport Manual
.
ISO 19901-3 Petroleum and natural gas industries – Specific requirements for offshore structures – Part 3: Topsides structure (currently in draft – expected to be issued 2003)
.
CAP 437 Offshore Helicopter Landing Areas – Guidance on Standards
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American Petroleum Institute - API RP 2L Recommended Practice for Planning, Designing and Constructing Heliports for Fixed Offshore Platforms
.
Classification Society codes for the design of offshore structures from Lloyd’s Register, DNV, BV, ABS, etc.
International standards such as ISO Codes, Eurocodes, or national standards, e.g. BS5950, NORSOK N-004 or AISC may be specified for detailed design.
9.3 LANDING SURFACE
9.3.1 Wood
Hardwood (Greenheart timber) was used for some helideck surfaces constructed in the early years of UKCS offshore installations. These wood surfaces can still be found on a few of the oldest platforms in the North Sea.
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