Section 2 Definitions
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, July 2022 - Part 9 Concrete Unit Structures - Chapter 2 Loads and Load Combinations - Section 2 Definitions

Section 2 Definitions

Parent topic: Chapter 2 Loads and Load Combinations

2.1 Permanent loads

2.1.1 The following can be considered permanent loads:
  • Weight of structure.
  • Weight of permanent ballast and equipment.
  • Buoyancy to support permanent loads.

2.1.2 Any long-term reduction in buoyancy due to water absorption into the concrete should be considered. Similarly, any long-term increase in weight due to absorption of internal fluids such as oil or ballast water should also be considered.

2.2 Live loads

2.2.1 Live loads are related to the operation of the unit and can vary in magnitude. The following can be considered as examples:
  • Pressure of liquid cargo and variable ballast.
  • Mooring loads for the still water condition.
  • Weight of stored materials and equipment.
  • Loads associated with process operation.
  • Crane and helicopter operations.
  • Buoyancy to support live loads.

2.3 Environmental loads

2.3.1 The assessment of environmental loads may be based on the results of model tests or by suitable direct calculation of the actual loads on the hull at the specific location, taking into account the following service related factors:
  1. Site-specific environmental conditions.
  2. Mooring loads due to the environment.
  3. Weathervaning with wave loadings predominantly from one direction.
  4. Long-term service effects at a fixed location.
  5. Range of tank loading conditions.

2.3.2 The characteristic value of the environmental load for a given limit state is to be the most unfavourable value calculated for the specified environmental return period, see Table 2.2.1 Basis for selection of return periods for environmental loads.

2.3.3 In assessing the values for wave, wind and current in a given environmental return period event, allowance can be made for joint probability, provided this can be documented.

2.3.4 All external water pressures due to waves above the unit’s maximum operating draught are to be considered as environmental loads.

2.3.5 Pressure heads due to wave impact loading at the fore end of concrete structures will be specially considered. In harsh environments a site-specific assessment is to be carried out to determine equivalent design pressure heads on the shell envelope. Where model tests are carried out, arrangements should be made to measure bow impact wave pressures, see also Pt 4, Ch 3, 4.1 General 4.1.5.

2.3.6 Loads from green seas on the deck and fore structure are to be considered as an environmental load. It is not necessary to include these loads in the overall bending moment for the hull strength, but they should be considered as a local ULS load on deck panels with the appropriate load factors. Minimum design deck pressures for this condition can be obtained from Pt 4, Ch 7 Watertight and Weathertight Integrity and Load Lines, except where model tests indicate higher loadings, see also Pt 4, Ch 3, 4.1 General 4.1.5 and Pt 10, Ch 1, 11 Green water and wave impact.

2.3.7 All hydrostatic pressures due to waves and internal sloshing forces are to be considered as environmental loads.

2.4 Deformation loads

2.4.1 Deformation loads on the structure shall be considered. These can result from the following sources amongst others:
  • Temperature.
  • Creep.
  • Shrinkage.
  • Pre-stressing.

2.4.2 For concrete structures the effects of cargo temperatures relative to seasonal ambient temperatures are to be considered for both sea and air temperatures, as appropriate for the section being assessed.

Table 2.2.1 Basis for selection of return periods for environmental loads

Limit State ULS SLS FLS PLS
Intact Damage
Load Accidental

Abnormal,

see Note 5

see Note 4
Environmental (E) 100 S see Note 1 Exp see Note 2

10 000

see Note 3

10 000 10
Accidental (A) — — —

10 000

see Note 3

— —

NOTES

1.For SLS, two conditions are required to be assessed, see Pt 9, Ch 3, 4.3 Analysis of sections for SLS
  • (a)Normal serviceability – this is selected such that the environmental loads will not be exceeded more than 100 times in the design life of the structure. In the absence of a more detailed assessment, for a typical 25-year design life, actions may be assumed to be 60% of the characteristic load for a 100-year return period event.
  • (b)Modified serviceability – 100-year return period event.

2.Exp = Expected Load History.

3.The combined return period of occurrence for the environmental and accidental loads is not to be greater than 10 000 years. In practice, dropped objects and collision loads against the hull will normally cause only local damage and hence need not be combined with environmental loads.

4.Where the PLS intact analysis shows little or no damage, the PLS damage condition need not be investigated.

5.The abnormal event is not a requirement for class but may be required to be assessed by some national or coastal state authorities.

2.5 Accidental and abnormal loads

2.5.1 Accidental loads are defined in Pt 4, Ch 3, 4.2 Definitions 4.2.4 and Pt 4, Ch 3, 4.16 Accidental loads. In addition, the failure of an oil cooling system, if fitted, is to be considered.

2.6 Characteristic value of loads

2.6.1 For the loads defined in this Section, the characteristic value of the individual loads are as follows:
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