Section
5 Helicopter landing areas
5.1 General
5.1.1 This Section gives the requirements for decks intended for helicopter
operations on all unit types.
5.1.3 Where helicopter decks are positioned so that they may be subjected to
wave impacts, the scantlings are to be considered in a realistic manner and
increased to the satisfaction of LR. Calculations are to be submitted for
consideration.
5.1.4 Where the landing area forms part of a weather or erection deck, the
scantlings are to be not less than those required for decks in the same
position.
5.2 Plans and data
5.2.1 Plans and data are to be submitted giving the arrangements, scantlings
and details of the helicopter deck. The type, size, weight and footprint of
helicopters to be used are also to be indicated.
5.2.2 Relevant details of the largest helicopters, for which the deck is
designed, are to be stated in the Operations Manual.
5.3 Arrangements
5.3.1 The landing area is to comply with applicable Regulations, International
Standards or to the satisfaction of the National Authority, with respect to size,
landing and take-off sectors of the helicopter, freedom from height obstructions,
deck markings, safety nets and lighting, etc.
5.3.2 The landing area is to have an overall coating of non-slip material or
other arrangements are to be provided to minimise the risk of personnel or
helicopters sliding off the landing area.
5.3.3 A drainage system is to be provided in association with a perimeter
guttering system or slightly raised kerb to prevent spilled fuel falling on to other
parts of the unit. The drains are to be led to a safe area.
5.3.4 A sufficient number of tie-down points are to be provided to secure the
helicopter.
5.3.5 Engine and boiler uptake arrangements are to be sited such that exhaust
gases cannot be drawn into helicopter engine intakes during helicopter take-off or
landing operations.
5.4 Landing area plating
5.4.1 Helideck support structures should be designed to carry all the loads
imposed on the helideck through to the primary structure of the unit. Helideck loads
derive from the parameters of the helicopter for which the helideck is intended
(landing impact forces and wheel spacing), the deck weight, plus environmental loads
(wind, snow and ice), and inertial loads due to unit movement, as applicable.
Additionally, the effects of live loads and loads arising from parked helicopters
(tied down) should be evaluated.
5.4.2 The designer of the support structure should ensure that all appropriate
load cases have been applied to the helideck, and that the resulting maximum load
cases are used in the design of the support structure. Similarly, it is important
that the load cases are accurately transposed to the design conditions for the
primary structure to which the support structure will be connected.
5.5 Load combination
5.5.1 The helicopter landing area is to be considered with respect to design
loads resulting from the following conditions:
- Emergency landing
- Normal operation and
- Helicopter at rest
5.5.2
Emergency landing The following loads are to be considered in helicopter
emergency landing condition.
- Helicopter landing dynamic loads: For an emergency landing, an
impact load of 2,5 x the maximum take-off weight (MTOW) of the helicopter
should be applied in any position on the landing area together with the
combined effects of Pt 4, Ch 6, 5.5 Load combination 5.5.2.(b) to Pt 4, Ch 6, 5.5 Load combination 5.5.2.(g) inclusive.
- Structural response factor for supporting
structure: The helicopter landing dynamic loads shall be increased by a
structural response factor to account for the sympathetic response of the
helideck structure. The factor to be applied for the design of the helideck
framing depends 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 of 1,3 shall be used.
- Area loads: A general area-distributed load of 0,5
kN/m2 shall be applied to allow for minor equipment left on
the helideck and for any snow and ice loads.
- Horizontal loads as a proportion of MTOW: Concentrated
horizontal imposed loads equivalent in total to half the maximum take-off
weight of the helicopter shall be applied at the locations of the main
undercarriages and distributed in proportion to the vertical loads at each
point. These shall be applied at deck level in the horizontal direction that
will produce the most severe load case for the structural component being
considered.
- Self weight of structure and fixed appurtenances: The self
weight of the helideck structure and fixed appurtenances supported by each
structural component concerned shall be evaluated.
- Wind loads: Wind loads on the helideck
structure shall be applied in the direction which, together with the
horizontal imposed loads, produces the most severe load case for the
structural component considered. The wind speed to be considered shall be
that restricting normal (non-emergency) helicopter operations at the
platform. Any vertical action on the helideck structure due to the passage
of wind over and under the helideck shall be considered.
- Inertial loads: The effect of accelerations
and dynamic amplification arising from the predicted motions of the fixed or
floating platform in a storm condition with a 10 year return period shall be
considered.
5.5.3
Normal operations The following loads are to be considered in helicopter
normal operation condition
- Helicopter landing dynamic loads: For a normal operation, an
impact load of 1,5 x the maximum take-off weight (MTOW) of the helicopter
should be applied in any position on the landing area together with the
combined effects of Pt 4, Ch 6, 5.5 Load combination 5.5.3.(b) to Pt 4, Ch 6, 5.5 Load combination 5.5.3.(g) inclusive.
- Structural response factor for supporting
structure: The helicopter landing dynamic loads shall be increased by a
structural response factor to account for the sympathetic response of the
helideck structure. The factor to be applied for the design of the helideck
framing depends 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 of 1,3 shall be used.
- Area loads: To allow for personnel, freight, refuelling
equipment and other traffic, snow and ice, rotor downwash, etc., a general
area load of 0,5 kN/m2 shall be included.
- Horizontal loads as proportion of MTOW: Concentrated horizontal
imposed loads equivalent in total to half the maximum take-off weight of the
helicopter shall be applied at the locations of the main undercarriages and
distributed in proportion to the vertical loads at each point. These shall
be applied at deck level in the horizontal direction that will produce the
most severe load case for the structural component being considered.
- Self weight of structure and fixed appurtenances.
- Wind loads: The 100 year return period wind loads on the
helideck structure shall be applied in the direction which produces the most
severe load case for the structural component considered.
- Inertial loads: The effect of accelerations
and dynamic amplification arising from the predicted motions of the fixed or
floating platform in a storm condition with a 10 year return period shall be
considered.
5.5.4
Helicopter at rest The following loads are to be considered in helicopter at
rest condition
- Helicopter static loads (local patch loads on landing gear): All
parts of the helideck accessible to helicopters shall be designed to support
a load equal to the MTOW of the helicopter at any location. This shall be
distributed at the undercarriage locations in proportion to the position of
the centre of gravity of the helicopter, taking account of possible
different positions and orientations of the helicopter.
- Area loads: To allow for personnel, freight, refuelling
equipment and other traffic, snow and ice, rotor downwash, etc., a general
area load of 2,0 kN/m2 shall be included.
- Horizontal loads from tie down helicopter, including wind loads
from a secured helicopter: Each tie-down shall be designed to resist the
calculated proportion of the total wind action on the helicopter imposed by
a storm wind with a minimum one year return period.
- Self weight of structure and fixed appurtenances.
- Wind loads: The 100 year return period wind loads on the
helideck structure shall be applied in the direction which produces the most
severe load case for the structural component considered.
- Inertial loads: The effect of accelerations and dynamic
amplification arising from the predicted motions of the fixed or floating
platform in a storm condition with a 10 year return period shall be
considered.
5.5.5 Deck plate and stiffeners shall be designed to limit the permanent
deflection (deformation) under helicopter emergency landing conditions to no more
than 2,5 % of the clear width of the plates between supports.
5.6 Helideck loading
5.6.1 The deck gross plate thickness, t, within the landing area is to
be not less than:
t = + 1,5 mm
where
|
= |
mm |
Figure 6.5.1 Tyre print chart
The plating is to be designed for the emergency landing case taking:
tonnes
where
are to be determined from Table 6.5.3 Deck plate thickness
calculation
f |
= |
1,15 for landing decks over manned spaces, e.g. deckhouses,
bridges, control rooms, etc. |
= |
1,0 elsewhere |
|
= |
the maximum all up weight of the helicopter, in tonnes |
|
= |
landing load on the tyre print, in tonnes;
- For helicopters with a single main rotor, , is to be taken as divided equally between the two main
undercarriage wheels.
- For helicopters with tandem main rotors, , is to be taken as distributed between all main undercarriage wheels
in proportion to the static loads they carry.
- For helicopters fitted with landing gear consisting of
skids, Pw
is to be taken as distributed in accordance with the actual load
distribution given by the airframe manufacturer. If this is unknown, is to be taken as 1/6 for each of the two forward contact points and
1/3 for each of the two aft contact points. The load
may be assumed to act as a 300 mm x 10 mm line load at each end of
each skid when applying Figure 6.5.1 Tyre print chart.
|
γ |
= |
0,6 generally. Factor to be specially considered where the
helicopter deck contributed to the overall strength of the unit |
Other symbols used in this Section are defined in Section 6 and in the
appropriate sub-Section.
- For wheeled undercarriages, the tyre print dimensions
specified by the manufacturer are to be used for the calculation. Where
these are unknown, it may be assumed that the print area is 300 x 300 mm and
this assumption is to be indicated on the submitted plans.
- For skids and tyres with an asymmetric print, the print is to
be considered oriented both parallel and perpendicular to the longest edge
of the plate panel and the greatest corresponding value of α taken from
Figure 6.5.1 Tyre print chart.
5.6.2 The plate thickness for aluminium decks is to be not less than:
t = 1,4+ 1,5 mm
where
is the mild steel thickness as determined from Pt 4, Ch 6, 5.6 Helideck loading 5.6.1.
Where the deck is fabricated using extruded sections with closely spaced
stiffeners the plate thickness may be determined by direct calculations but the
minimum deck thickness is to include 1,5 mm wear allowance. If the deck is protected
by closely spaced grip/wear treads the wear allowance may be omitted.
5.7 Deck stiffening and supporting
structure
5.7.2 In addition to the requirements of Pt 4, Ch 6, 5.5 Load combination 5.5.1, the structure supporting helicopter decks is
to be designed to withstand the loads imposed on the structure due to the motions of
the unit. For self-elevating units, the motions are not to be less than those
defined for transit conditions in Pt 4, Ch 4, 3.10 Legs in field transit conditions and Pt 4, Ch 4, 3.11 Legs in ocean transit conditions. The stress levels are to comply with load case
3 in Pt 4, Ch 6, 5.7 Deck stiffening and supporting structure 5.7.2, see also
Pt 4, Ch 6, 5.1 General 5.1.3.
Table 6.5.1 Design load cases for deck
stiffening and supporting structure
Load cases
|
Load
|
Landing area
|
Supporting structure
(See Note 1)
|
Area load, in kN/m2
|
Helicopter patch load (See Note 2)
|
Self-weight
|
Wind load, return period in years
|
Inertia load, return period in years
|
(1) Helicopter emergency
landing
|
0,5
|
2,5
|
|
See
Pt 4, Ch 6, 5.5 Load combination 5.5.2
|
10
|
(2) Normal
operation
|
0,5
|
1,5
|
|
100
|
10
|
(3) Helicopter at
rest
|
2,0
|
|
|
100
|
10
|
Symbols
|
and f as defined in Pt 4, Ch 6, 5.6 Helideck loading 5.6.1
|
= structural self-weight of helicopter
platform
|
NOTES
|
1. For the design of the supporting structure for
helicopter platforms applicable horizontal load, self-weight,
wind load and inertia load are to be added to the landing area
loads. Where applicable, thermal loads due to the differences
between design and operating temperatures are to be considered
for aluminium alloy helidecks.
|
2. The helicopter is to be so positioned as to
produce the most severe loading condition for each structural
member under consideration.
|
3. For the emergency landing and normal operation,
helicopter patch load shall be increased by a suitable
structural response factor depending upon the natural frequency
of the helideck structure. It is recommended that a structural
response factor of 1,3 should be used unless further information
allows a lower factor to be calculated. For helidecks
constructed of aluminium alloys, the value of the structural
response factor is to be specially considered.
|
Table 6.5.2 Permissible stresses for
deck stiffening and supporting structure
Load case
See
Table 6.5.1 Design load cases for deck
stiffening and supporting structure
|
Permissible stresses, in N/mm2
|
Deck
secondary structure
(beams, longitudinals, deck
plating )
See Notes
1 and 2
|
Primary structure
(transverses, girders, pillars, trusses)
|
All
structure
|
Bending
|
Combined bending
and axial
|
Shear
|
(1) Helicopter
emergency landing
|
235/k
|
211,5,5/k
|
0,9σc
|
|
(2) Normal
operation
|
176/k
|
153/k
|
0,5σc
|
(3) Helicopter at
rest
|
176/k
|
153/k
|
0,5σc
|
Symbols
|
k = a material factor:
|
= as defined in Pt 4, Ch 2, 1.2 Steel for steel members
|
= as defined in Pt 4, Ch 2, 1.3 Aluminium for aluminium alloy
members
|
σc = yield stress, 0,2% proof stress or
critical buckling stress, in N/mm2, whichever is the
lesser
|
NOTES
|
1. Lower permissible stress levels may be required
where helideck girders and stiffening contribute to the overall
strength of the unit. Special consideration will be given to
such cases.
|
2. When
determining bending stresses in secondary structure, for
compliance with the above permissible stresses, 100% end fixity
may be assumed.
|
Table 6.5.3 Deck plate thickness
calculation
Symbols
|
Expression
|
a, s, u and v as defined in Figure 6.5.1 Tyre print chart
|
|
|
= load, in tonnes, on the tyre print. For closely
spaced wheels the shaded area shown in Figure 6.5.1 Tyre print chart may be taken
as the combined print
|
φ1 = patch
aspect ratio correction factor
|
= 1,0
|
for u ≤ (a –
s)
|
φ2 = panel
aspect ratio correction factor
|
=
|
for a ≥ u >
(a – s)
|
φ3 = wide
patch load factor
|
= 0,77
|
for u >
a
|
|
= 1,0
|
for v < s
|
= 0,6 + 0,4
|
for 1,5 > > 1,0
|
|
= 1,2
|
for ≥ 1,5
|
5.7.4 When the deck is constructed of extruded aluminium alloy sections, the
scantlings and connections between structural members will be specially considered
on the basis of this Section.
5.7.5 Where a grillage arrangement is adopted for the platform stiffening, it
is recommended that direct calculation procedures be used.
5.8 Bimetallic connections
5.8.1 Where aluminium alloy platforms are connected to steel structures,
details of the arrangements in way of the bimetallic connections are to be
submitted.
|