2.6.1 The hull strength should be evaluated in
the elevated position for the specified environmental conditions with
maximum gravity loads aboard and with the unit supported by all legs.
The distribution of these loads in the hull structure should be determined
by a method of rational analysis. Scantlings should be calculated
on the basis of this analysis, but should not be less than those required
for other modes of operation.
2.6.2 The unit should be so designed as to enable
the hull to clear the highest design wave including the combined effects
of astronomical and storm tides. The minimum clearance may be the
lesser of either 1.2 m or 10% of the combined storm tide, astronomical
tide and height of the design wave above the mean low water level.
2.6.3 Legs should be designed to withstand the
dynamic loads which may be encountered by their unsupported length
while being lowered to the bottom, and also to withstand the shock
of bottom contact due to wave action on the hull. The maximum design
motions, sea state and bottom conditions for operations to raise or
lower the hull should be clearly stated in the operating manual.
2.6.4 When evaluating leg stresses with the unit
in the elevated position, the maximum overturning moment on the unit
due to the most adverse combination of applicable environmental and
gravity loadings should be considered.
2.6.5 Legs should be designed for the most severe
environmental transit conditions anticipated including wind moments,
gravity moments and accelerations resulting from unit motions. The
Administration should be provided with calculations, an analysis based
on model tests, or a combination of both. Acceptable transit conditions
should be included in the operating manual. For some transit conditions,
it may be necessary to reinforce or support the legs, or to remove
sections to ensure their structural integrity.
2.6.6 Structural members which transmit loads
between the legs and the hull should be designed for the maximum loads
transmitted and so arranged as to diffuse the loads into the hull
structure.
2.6.7 When a mat is utilized to transmit the bottom
bearing loads, attention should be given to the attachment of the
legs so that the loads are diffused into the mat.
2.6.8 Where tanks in the mat are not open to the
sea, the scantlings should be based on a design head using the maximum
water depth and tidal effects.
2.6.9 Mats should be designed to withstand the
loads encountered during lowering including the shock of bottom contact
due to wave action on the hull.
2.6.10 The effect of possible scouring action
(loss of bottom support) should be considered. The effect of skirt
plates, where provided, should be given special consideration.
2.6.11 Except for those units utilizing a bottom
mat, the capability should be provided to pre-load each leg to the
maximum applicable combined load after initial positioning at a site.
The pre-loading procedures should be included in the operating manual.
2.6.12 Deckhouses located near the side shell
of a unit may be required to have scantlings similar to those of an
unprotected house front. Other deckhouses should have scantlings suitable
for their size, function and location.