Section 4 Load cases and load combinations
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Code for Offshore Personnel Transfer Systems, July 2022 - Chapter 1 Offshore Personnel Transfer Systems - Section 4 Load cases and load combinations

Section 4 Load cases and load combinations

Parent topic: Chapter 1 Offshore Personnel Transfer Systems

4.1 General

4.1.1 For the structural design of the OPTS the following four cases are required to be considered:

  1. Case 1: In-service - OPTS engaged in personnel or cargo transfer operations (without wind).
  2. Case 2: In-service - OPTS engaged in personnel or cargo transfer operations (with wind).
  3. Case 3: Out-of-service - OPTS engaged in in-field transit or general transit/voyage (stowage/survival) conditions (with wind).
  4. Case 4: In-service or out-of-service or load testing - OPTS subjected to emergency or exceptional conditions (with wind).

4.2 Operational load combinations

4.2.1 Typical in-service load combinations are defined as follows and are associated with load combination Cases 1 and 2:
  1. normal personnel transfer operations;
  2. normal cargo operations for OPTS with cargo handling facilities; and
  3. combinations of load combinations (a) and (b) will be specially considered.

4.2.2 Load combination cases.

  • Case 1a and Case 1b

    Load combination Case 1a is defined as being the personnel transfer in-service design case while load combination Case 1b is defined as being the cargo operational mode both without the effects of wind. The conditions, configurations, effects and loads to be considered as a minimum are given in Table 1.4.1 Conditions, configurations, effects and load types.

  • Case 2a and Case 2b

    Load combination Case 2a is defined as being the personnel transfer in-service design case while load combination Case 2b is defined as being the cargo operational mode both including the effects of wind. The conditions, configurations, effects and loads to be considered as a minimum are given in Table 1.4.1 Conditions, configurations, effects and load types.

4.3 General transit/voyage (stowage/survival) and in-field transit load combinations

4.3.1 In-field transit and general transit/voyage (stowage/survival) out-of-service load combinations are defined as follows and are associated with load combination Case 3:

  1. General transit (stowage/survival)

    General transit is usually defined as the voyage from one field of operation to another where extreme (survival) environmental conditions may occur and the OPTS needs to be subjected to maximum stowage arrangement.

  2. In-field transit

    In-field transit is usually defined as the voyage within a defined field of operation where the mothership is moving within the field from one operational location to another.

4.3.2 Load combination case.

4.4 In-service and out-of-service emergency/exceptional load combinations

4.4.1 The following in-service and out-of-service emergency and exceptional scenarios, loads and load combinations shall be taken into consideration as a minimum and are associated with load combination Case 4, such as:

  1. system fault scenarios (e.g. software failure modes in case those have the potential to lead to exceptional loads);
  2. proof load testing;
  3. failure of the power supply;
  4. failure of control system;
  5. failure of components;
  6. emergency disconnection (lift-off);
  7. injured person to be rescued (e.g. two persons plus one person on a stretcher);
  8. failure of mechanical components; and
  9. ‘redundancy situations’ (e.g. failure of one hydraulic cylinder in a two hydraulic cylinder design).
4.4.2 Load combination cases.
  • Case 4a, Case 4b and Case 4c

    Load combination Case 4a is defined as being the personnel transfer emergency design case, load combination Case 4b is defined as being the cargo emergency design case and load combination Case 4c is defined as being the proof load testing design case. The effects and loads to be considered as a minimum for exceptional and emergency cases are given in Table 1.4.1 Conditions, configurations, effects and load types.

4.5 Load combination overview

4.5.1 Table 1.4.1 Conditions, configurations, effects and load types provides an overview of what conditions/configurations, effects and loads are to be considered in which load combination case. Further details can be found in Ch 1, 4.2 Operational load combinations, Ch 1, 4.3 General transit/voyage (stowage/survival) and in-field transit load combinations and Ch 1, 4.4 In-service and out-of-service emergency/exceptional load combinations.

Table 1.4.1 Conditions, configurations, effects and load types

Condition/configuration, effect or load type Reference In-Service (operation) Note 1 Out-of-Service

(stowage/ survival)

Note 1 		In-Service or Out-of-Service

(emergency/ exceptional)

Note 1
Case 1a Case 1b Case 2a Case 2b Case 3 Case 4a Case 4b Case 4c
Dead load Note 3 X X X X X X X X
Loads due to personnel transfer operations Note 4 X (X)

Note 2

X (X)

Note 2

–– X (X)

Note 2

 ––
Loads due to cargo handling operations Note 5 (X) Note 2 X (X) Note 2 X –– (X)

Note 2

 X ––
Proof load test loads Note 6 –– –– –– –– –– –– –– X
Mothership accelerations (e.g. related to the specified values of H1/3 for in-service, out-of-service and exceptional conditions, as applicable) Note 7 X X X X X X X ––
Mothership static inclinations Note 8 X X X X X X X ––
Equipment modes (condition, configurations, motions, accelerations, etc.) and resulting loads Note 9 X X X X X X X X
Loads required as a result of the risk assessment Note 10 X X X X X X X X
Other loads, not listed in the above, demanded by the actual design of the OPTS and/or by environmental conditions and/or by the specific mothership design Note 11 X X X X X X X X
Effects of wind Note 12 –– –– X X X X X ––
Exceptional and emergency scenarios and loads Note 13 –– –– –– –– –– X X ––
Loads as required considering the individual emergency scenario –– –– –– –– –– X X ––
Loads due to stowage of the OPTS Note 14 –– –– –– –– X –– –– ––
Note 1:

‘X’ = Applicable

‘––‘ = Not applicable

Note 2: Applicable in case personnel handling occurs together with cargo handling on the gangway.
Note 3: See Ch 1, 3.2 Dead load.
Note 4: See Ch 1, 3.3 Safe Working Load, Ch 1, 3.4 Uniformly Distributed Load, Ch 1, 3.5 Loads on floorings, Ch 1, 3.6 Loads on platforms and walkways and Ch 1, 3.7 Loads on handrails.
Note 5: See Ch 1, 3.3 Safe Working Load.
Note 6: See Ch 1, 13.1 Testing.
Note 7: See Ch 1, 3.11 Mothership motions and accelerations.
Note 8: See Ch 1, 3.12 Static inclinations.
Note 9: See Ch 1, 3.13 Dynamic forces due to travelling, slewing, telescoping and luffing.
Note 10: See Ch 1, 10 Risk assessment and Ch 1, 3.22 Special loads.
Note 11: See Ch 1, 3.17 Snow and ice, Ch 1, 3.18 Temperature effects, Ch 1, 3.20 System internal forces, Ch 1, 3.21 Contact loads and Ch 1, 3.22 Special loads.
Note 12: See Ch 1, 3.14 Wind.
Note 13: See Ch 1, 3.16 Emergency scenarios and loads, Ch 1, 10 Risk assessment and Ch 1, 3.22 Special loads.
Note 14: See Ch 1, 3.15 Stowage.

4.6 Stress factors

4.6.1 The stress factor, F, used to determine e.g. the allowable stresses, shall be as per Table 1.4.2 Stress factors for the defined load cases.

Table 1.4.2 Stress factors for the defined load cases

Load case Case 1a/1b Case 2a/2b Case 3 Case 4a/4b/4c
  In-Service

(operation)

 Out-of-Service

(stowage/ survival)

 In-Service or Out-of-Service

(emergency/ exceptional)
Stress factor 0,67 0,75 0,85

4.6.2 Alternatively, the concept of load and resistance factor design may be applied. The partial safety factors for the loads and the combination of loads are to be agreed with LR. The partial safety factor for the resistance side shall be taken as γm = 1,10. See Ch 1, 5.1 General 5.1.2.

4.7 Load case combinations

4.7.1 The combinations of loads and load combination cases are given in Table 1.4.1 Conditions, configurations, effects and load types. The combinations given shall be used even if the concept of load and resistance factor design is not applied.

4.7.2 The risk coefficients are also to be applied as defined in Ch 1, 3.8 Risk coefficient.

4.8 Offshore cranes

4.8.1 If the OPTS is also used as a conventional offshore crane and/or handling of personnel in a personnel containment, then the loads and load combinations of the Code for Lifting Appliances in a Marine Environment, July 2022 for offshore cranes are to be taken into consideration. See Ch 4, 3 Offshore cranes of the Code for Lifting Appliances in a Marine Environment, July 2022.

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