Section 1 Design Loads

101. Loads

1. In regard to loads in determining the scantlings of structural members and in calculating mooring forces for the units, unless otherwise specified elsewhere, the following loads are to be taken into account, where applicable.

(1) Deck loads

(2) Static loads such as water pressure in still water, buoyancy, dead load, etc.

(3) Wind loads

(4) Wave loads

(5) Loads caused by tide and current

(6) Loads caused by floating ice

(7) Loads caused by snow and ice accumulation

(8) Loads caused by earthquake in the case of bottoming-type units

(9) Impact loads caused when touching sea bed

(10) Loads caused b

(11) Loads caused y

mooring

mooring of tenders

(12) Loads caused by towing

(13) Loads caused by operation

(14) Loads due to helicopter landing

(15) Loads due to increase of resistance by marine growth

(16) Other loads considered necessary by the Society

2. The

modes of operation for each unit are to be investigated using realistic loading conditions in-

cluding gravity loading with relevant environmental loading for its intended areas of operation. The following environmental considerations should be included where applicable: wind, wave, current, ice, seabed conditions, temperature, fouling and earthquake.

3. Drawings of a unit are to be approved for the specified environmental conditions. Where possible, the above design environmental conditions apply to units and structural members should be based upon significant data with a period of recurrence of at least 50 years for the most severe antici- pated environment.

4. If a unit is restricted to seasonal operations in order to avoid excessive wind and wave, such sea- sonal limitations must be specified.

102. Wind loads

1. The design wind velocity used in determining the wind loads may be specified by the Owner, but is not to be less than 25.8 mÕsec (50 knots ). However, the design wind velocity for the units in- tended for unrestricted services and operating sea areas is not to be less than 36 mÕsec (70 knots) for the operating condition and not to be less than 51.5 mÕsec (100 knots) for the severe storm

condition, specified

2. The wind pressure may be determined

in Ch 1, 207., respectively.

Č is to be obtained from the following formula. The wind pressure, however, from the wind tunnel test considered appropriate by the Society.

ČŅLǾJǼᾜ

ᾯ

Ǽ ᾬĐĪ ×ÌLŇĮ

NkNÕm ĪŃ

Đ :

Č :

Ǽᾜ :

Design wind velocity specified in Par 1 (mÕsec). Air mass density (1.222 kgÕmĮ)

Height coefficient given by Table 4.1 depending on the vertical height in metres at the

location under consideration, where the vertical height is a vertical distance from sea sur-

Ch 4 Design Condition Ch 4

face to the geometric centre of the projected area A specified in the following Par 3.

Ǽᾯ : Shape coefficient given by Table 4.2 depending on the shape of structural members.

Table 4.1 Height Coefficient Ǽᾜ Table 4.2 Shape Coefficient Ǽᾯ

3. The wind load  is not to be less than obtained from the following formula with regard to each structural member of the unit. In addition, the resultant force and its acting point are to be de- termined for each wind direction. However, the wind force may be determined from the wind tun- nel test considered appropriate by the Society.

 Ņ Č × A NkNŃ

Č : Wind pressure specified in Par 2 (kNÕmĪ).

A : Projected area of all exposed structural members on a plane perpendicular to each wind di- rection in the upright condition or, if necessary, in the heeling condition (mĪ). In determin-

ing the projected area, the following requirements are to be applied.

(1) In the case of units with columns, the projected areas of all columns should be included. For self- elevating units, the projected areas of all legs or columns are to be included. Where, how- ever, the legs are of open truss work which does not block wind passage, the above mentioned projected areas may be determined according to the requirements in (3).

(2) The projected areas of deckhouses, other structural members, cranes, etc. are to be separately calculated. Where, however, two or more structures such as deckhouses and the like are closely located, they may be considered as one block and their projected areas may be considered as a

projected block area perpendicular to each wind direction. In this case, the shape coefficient Ǽᾯ

is to be taken as 1.1.

(3) The projected areas in case where derrick towers, booms, masts, etc. are of open truss work

may be taken as 60 % of the projected block areas perpendicular to each wind direction assum- ing that they are not of open truss work.

(4) Areas exposed due to heel, should be included using the appropriate shape coefficients.

Ch 4 Design Condition Ch 4

103. Wave loads

1. The design wave height to be used for wave load calculation may be specified by the Owner un- der the approval of the Society.

2. The design wave period to be used for wave load calculation is to be the period which gives the maximum effect to the unit.

3. If necessary, the velocities of current and tide are to be added vectorially to the wave particle velocity.

4. In calculating wind loads, the following requirements are to be applied.

(1) The wave loads are to be calculated, based on acceptable wave theories appropriate to the de- sign depth of water at the operation area subject to the approval by the Society. The wave loads, however, may be determined from the tank test approved by the Society on a model of the unit.

(2) Waves from all directions are to be considered on the unit.

(3) The wave loads produced by shipping water on the deck, the loads acting directly on the im- mersed elements of the unit and the loads resulting from heeled positions or accelerations due

to its motion are also to be considered.

(4) The vibration induced by waves is also to be considered.

104. Current loads

Consideration is to be given to the possible superposition of current and waves. In this case where this superposition is deemed necessary, the current velocity is to be added vectorially to the wave particle velocity and the resultant velocity is to be used to compute the total force.

105. Loads due to vortex shedding

The flutters of immersed structural members due to vortex shedding are also to be considered.

106. Deck loads

For deck loads, uniform and concentrated loads on the respective portions of the deck in each mode of operation and transit condition are to be taken into account. The values of the uniform loads, however, are not to be less than given in Table 4.3.

Table 4.3 Deck Loads