MODU CODE – 2009

2.3 Design loads

2.3.1 The modes of operation for each unit are to be investigated using realistic loading conditions including 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.

2.3.2 Where possible, the above design environmental conditions should be based upon significant data with a period of recurrence of at least 50 years for the most severe anticipated environment.

2.3.3 Results from relevant model tests may be used to substantiate or amplify calculations.

2.3.4 Limiting design data for each mode of operation should be stated in the operating manual.


Wind loading

2.3.5 Sustained and gust wind velocities, as relevant, should be considered when determining wind loading. Pressures and resultant forces should be calculated by the method referred to in section 3.2 or by some other method to the satisfaction of the Administration.


Wave loading

2.3.6 Design wave criteria should be described by design wave energy spectra or deterministic design waves having appropriate shape and size. Consideration should be given to waves of lesser height, where, due to their period, the effects on structural elements may be greater.

2.3.7 The wave forces utilized in the design analysis should include the effects of immersion, heeling and accelerations due to motion. Theories used for the calculation of wave forces and the selection of coefficients should be to the satisfaction of the Administration.


Current loading

2.3.8 Consideration should be given to the interaction of current and waves. Where necessary, the two should be superimposed by adding the current velocity vectorially to the wave particle velocity. The resultant velocity should be used in calculating the structural loading due to current and waves.


Loading due to vortex shedding

2.3.9 Consideration should be given to loading induced in structural members due to vortex shedding.


Deck loading

2.3.10 A loading plan should be prepared to the satisfaction of the Administration showing the maximum design uniform and concentrated deck loading for each area for each mode of operation.


Other loadings

2.3.11 Other relevant loadings should be determined in a manner to the satisfaction of the Administration.


2.4 Structural analysis

2.4.1 Sufficient loading conditions for all modes of operation should be analysed to enable the critical design cases for all principal structural components to be evaluated. This design analysis should be to the satisfaction of the Administration.

2.4.2 The scantlings should be determined on the basis of criteria which combine, in a rational manner, the individual stress components in each structural element. The allowable stresses should be to the satisfaction of the Administration.

2.4.3 Local stresses, including stresses caused by circumferential loading on tubular members, should be added to primary stresses in evaluating combined stress levels.

2.4.4 The buckling strength of structural members should be evaluated where appropriate.

2.4.5 Where deemed necessary by the Administration, a fatigue analysis based on intended operating areas or environments should be provided.

2.4.6 The effect of notches, local stress concentrations and other stress raisers should be allowed for in the design of primary structural elements.

2.4.7 Where possible, structural joints should not be designed to transmit primary tensile stresses through the thickness of plates integral with the joint. Where such joints are unavoidable, the plate material properties and inspection procedures selected to prevent lamellar tearing should be to the satisfaction of the Administration.


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