Section 6 Self-elevating Units

601. Application

The requirements in this Section apply to self-elevating units.

602. Overall strength

The overall strength of the unit is to be in accordance with the requirements in The unbalanced supported condition by the legs, if necessary, is to be considered.

401. and 412.

603. Legs

Legs are to be in accordance with the requirements in the following, in addition to the require- ments in 602. However, with regard to the motions of the unit and legs, they may be determined by an analytical method or from a model experiment deemed appropriate by the Society.

(1) Legs are to be either shell type or truss type and, as a rule, footings or bottom mats are to be fitted. Where footings or bottom mats are not fitted, proper consideration is to be given to the leg penetration of the sea bed and the end fixity of the leg. In strength calculation of such a leg, the leg is to be assumed as pin-supported at a position at least 3 metres below the sea bed.

(2) Legs in the field transit condition are to be in accordance with the followings. The field transit condition means the condition which does not exceed a twelve-hours voyage between two areas in protected locations or locations where the unit may be safely elevated. However, during any portion of the move, the unit is to be capable of arriving at a protected location or a location where the unit may be safely elevated within six hours.

(A) The legs are to have sufficient strength for the bending moment obtained from the follow-

ing formulae :

kN - m

: Dynamic bending moment caused by a 6° single amplitude of roll or pitch at the

natural period of the unit (kN - m ).

: Static bending moment due to gravity caused by a 6° legs' angle of inclination (kN - m ).

(B) The legs are to be investigated for any proposed leg arrangement with respect to vertical position. Such investigations are to include strength and stability aspects.

(3) Legs in the ocean transit condition are to be designed in accordance with the followings :

(A) The legs are to be designed for acceleration and gravity moments resulting from the mo- tions in the severest anticipated environmental transit condition, together with corresponding wind moments.

(B) The legs are to have sufficient strength for the bending moment obtained from the follow-

kN - m

: Dynamic bending moment caused by a 15° single amplitude of roll or pitch at a

10-second period (kN -m ).

: Static bending moment due to gravity caused by a 15° legs' angle of inclination (kN -m ).

(C) For ocean transit condition, it may be necessary to reinforce or support the legs, or to re- move sections of them.

(D) The approved condition is to be included in Operating Booklet.

(4) When computing leg stresses, while in the elevated position, the maximum overturning load on

the unit, using the most adverse combination of applicable variable loadings together with the

deflections of the legs are to be taken into account .

(5) Leg scantlings are to be determined in accordance with a method of rational analysis, to the satisfaction of the Society.

604. Hull structure

1. The hull is to be considered as a complete structure having sufficient strength to resist all induced stress while in the elevated position and supported by all legs.

2. The scantlings of the respective hull structural members are to be in accordance with the require- ments in Sec 4 with reference to the loads prescribed in Sec 3 in addition to 602.

3. The hull structure, including the parts of the well, etc., is to be good in the continuity of longi- tudinal strength and transverse strength.

4. Scantlings of units having other than rectangular hull configurations are to be subject to special consideration.

605. Bottom mats

1. The construction of bottom mats is to be designed so that loads transmitted evenly distributed to the respective parts of the mats.

from the legs may be

2. The thickness of shell

plating of the bottom mats without opening to the

sea and scantlings of

shell stiffeners are not

to be less than determined by the requirements in

413.

2 and Par 3. In

this case, the top of is at the water level at flood tide, and the top of sign wave height in the severe storm condition above the water level at

0.6 times the de- design water depth.

3. The scantlings of watertight bulkheads and their stiffeners be less than determined by the requirements in Pt 3, Ch

provided in the bottom mats are not to

14 of Rules for the Classification of

Steel Ships. In this case, the top of is to be substituted to the top of specified in Par 2.

4. Where the unit is resting on the sea bed, the effects of scouring are also to be considered. The ef- fects of skirt plates, where provided, are to be specially considered.

5. Mats are to be designed to withstand the shock of touching bottom while the unit is afloat and subject to wave motions.

606. Deck elevating apparatus and load carrying members

1. Operating device, mechanism, strength and safety equipment of the deck elevating apparatus are to be in accordance with the requirements in Ch 5, 204.

2. Load carrying members which transmit loads from the legs to the hull are to have sufficient strength for the loads prescribed in 603. and Par 3.

3. Load carrying members are to be arranged so that loads transmitted from the legs are properly dif- fused into the hull structure.

607. Deckhouses

1. Deckhouses are to have sufficient strength for their size, function and locations and are to be con- structed to approval plans.

2. General scantlings are to comply with the requirements in Pt 3, Ch 17 of Rules for the Classification of Steel Ships and the scantlings of enclosed spaces are to comply with the re- quirements for bulkheads of unprotected house fronts in Pt 3, Ch 17 of Rules for the Classification of Steel Ships.

608. Sea bed condition

Sea bed conditions are to be based upon the designer's assumptions, and these assumptions are to be recorded in the Operating Booklet. The operator is to be watchful against that actual conditions do not impose more severe loadings on the unit.

609. Wave clearance

The unit is to be designed for a crest clearance of either 1.2 m , or 10 % of the combined storm tide, astronomical tide and height of the maximum wave crest above the mean low water level, whichever is the smaller, between the underside of the unit in the elevated position and the crest of the design wave. This crest elevation is to be measured above the level of the combined astro- nomical and storm tides.

610. Preload capability

For units without bottom mats, all legs are to have the capability of being preloaded to the max- imum applicable combined gravity plus overturning load. The approved preload procedure should be included in the Operating Booklet.