Petroleum and natural gas industries -- Fixed steel offshore structures

This document specifies requirements and provides recommendations applicable to the following types of fixed steel offshore structures for the petroleum and natural gas industries: ? caissons, free-standing and braced; ? jackets; ? monotowers; ? towers. In addition, it is applicable to compliant bottom founded structures, steel gravity structures, jack-ups, other bottom founded structures and other structures related to offshore structures (such as underwater oil storage tanks, bridges and connecting structures). This document contains requirements for planning and engineering of the design, fabrication, transportation and installation of new structures as well as, if relevant, their future removal. NOTE 1 Specific requirements for the design of fixed steel offshore structures in arctic environments are presented in ISO 19906. NOTE 2 Requirements for topsides structures are presented in ISO 19901-3; for marine operations in, ISO 19901‑6; for structural integrity management, in ISO 19901-9 and for the site-specific assessment of jack-ups, in ISO 19905‑1.

Industries du pétrole et du gaz naturel -- Structures en mer fixes en acier

General Information

Status
Published
Publication Date
11-Nov-2020
Current Stage
6060 - International Standard published
Start Date
16-May-2020
Completion Date
12-Nov-2020
Ref Project

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INTERNATIONAL ISO
STANDARD 19902
Second edition
2020-11
Petroleum and natural gas
industries — Fixed steel offshore
structures
Industries du pétrole et du gaz naturel — Structures en mer fixes
en acier
Reference number
ISO 19902:2020(E)
ISO 2020
---------------------- Page: 1 ----------------------
ISO 19902:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 19902:2020(E)
Contents Page

Foreword ....................................................................................................................................................................... xiv

Introduction ................................................................................................................................................................ xvii

1 Scope ....................................................................................................................................................................... 1

2 Normative references ....................................................................................................................................... 1

3 Terms and definitions ....................................................................................................................................... 2

4 Symbols ............................................................................................................................................................... 10

5 Abbreviated terms .......................................................................................................................................... 14

6 Overall considerations ................................................................................................................................... 16

6.1 Types of fixed steel offshore structure ....................................................................................... 16

6.1.1 General .................................................................................................................................. 16

6.1.2 Jackets ................................................................................................................................... 16

6.1.3 Towers ................................................................................................................................... 17

6.1.4 Jack-ups ................................................................................................................................. 17

6.2 Planning ................................................................................................................................................. 18

6.2.1 General .................................................................................................................................. 18

6.2.2 Hazards ................................................................................................................................. 18

6.2.3 Designing for hazards ...................................................................................................... 19

6.2.4 Design situations and criteria ....................................................................................... 19

6.2.5 Design for inspection and maintenance .................................................................... 19

6.2.6 Foundations and active geological processes ......................................................... 20

6.2.7 Regulations .......................................................................................................................... 20

6.3 Service and operational considerations .................................................................................... 20

6.3.1 General considerations ................................................................................................... 20

6.3.2 Water depth ......................................................................................................................... 20

6.3.3 Structural configuration ................................................................................................. 20

6.3.4 Access and auxiliary systems ........................................................................................ 21

6.4 Safety considerations........................................................................................................................ 21

6.5 Environmental considerations ...................................................................................................... 21

6.5.1 General .................................................................................................................................. 21

6.5.2 Selecting design metocean parameters and action factors ................................ 22

6.6 Exposure levels ................................................................................................................................... 22

6.7 Assessment of existing structures................................................................................................ 23

6.8 Structure reuse ................................................................................................................................... 23

7 General design requirements ...................................................................................................................... 23

7.1 General ................................................................................................................................................... 23

7.2 Material properties for steel .......................................................................................................... 24

7.3 Incorporating limit states ............................................................................................................... 24

7.4 Determining design situations ...................................................................................................... 24

7.5 Structural modelling and analysis ............................................................................................... 25

7.6 Design for pre-service and removal situations ....................................................................... 25

7.7 Design for the in-place situation................................................................................................... 25

7.8 Determination of component resistances ................................................................................. 25

7.8.1 General .................................................................................................................................. 25

7.8.2 Physical testing to derive resistances ........................................................................ 26

7.8.3 Resistances derived from computer simulations validated by physical

testing .................................................................................................................................... 26

© ISO 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 19902:2020(E)
7.8.4 Resistances derived from computer simulations validated against

design formulae ................................................................................................................. 26

7.8.5 Resistances derived from unvalidated computer simulations ........................ 26

7.9 Strength and stability checks ........................................................................................................ 26

7.9.1 Action and resistance factors ....................................................................................... 26

7.9.2 Strength and stability equations ................................................................................. 26

7.9.3 Unfactored actions ........................................................................................................... 27

7.10 Robustness ........................................................................................................................................... 27

7.10.1 General ................................................................................................................................. 27

7.10.2 Damage tolerance ............................................................................................................. 27

7.11 Reserve strength ................................................................................................................................ 28

7.11.1 New structures ................................................................................................................... 28

7.11.2 Existing structures ........................................................................................................... 29

7.12 Indirect actions ................................................................................................................................... 29

7.13 Structural reliability analysis........................................................................................................ 29

8 Actions for pre-service and removal situations ................................................................................... 30

8.1 General .................................................................................................................................................. 30

8.1.1 Coverage ............................................................................................................................... 30

8.1.2 Design situations ............................................................................................................... 30

8.1.3 Actions .................................................................................................................................. 30

8.2 General requirements ...................................................................................................................... 31

8.2.1 Weight control ................................................................................................................... 31

8.2.2 Dynamic effects.................................................................................................................. 31

8.2.3 Action effects ...................................................................................................................... 31

8.3 Onshore lifting .................................................................................................................................... 33

8.3.1 General ................................................................................................................................. 33

8.3.2 Dynamic effects.................................................................................................................. 33

8.3.3 Effect of tolerances ........................................................................................................... 34

8.3.4 Multi-crane lift ................................................................................................................... 34

8.3.5 Local factor .......................................................................................................................... 34

8.3.6 Member and joint strengths .......................................................................................... 35

8.3.7 Lifting attachments .......................................................................................................... 35

8.3.8 Slings, shackles and fittings .......................................................................................... 36

8.4 Fabrication ........................................................................................................................................... 36

8.5 Loadout .................................................................................................................................................. 36

8.5.1 Direct lift .............................................................................................................................. 36

8.5.2 Horizontal movement onto vessel .............................................................................. 36

8.5.3 Self-floating structures ................................................................................................... 37

8.6 Transportation ................................................................................................................................... 37

8.6.1 General ................................................................................................................................. 37

8.6.2 Metocean conditions ........................................................................................................ 37

8.6.3 Determination of actions ............................................................................................... 37

8.6.4 Other considerations ....................................................................................................... 38

8.7 Installation ........................................................................................................................................... 38

8.7.1 Lifted structures ................................................................................................................ 38

8.7.2 Launched structures ........................................................................................................ 38

8.7.3 Crane assisted uprighting of structures ................................................................... 38

8.7.4 Submergence pressures ................................................................................................. 38

8.7.5 Member flooding ............................................................................................................... 39

8.7.6 Actions on the foundation during installation ....................................................... 39

9 Actions for in-place situations .................................................................................................................... 39

9.1 General .................................................................................................................................................. 39

9.2 Permanent actions (G) and variable actions (Q) .................................................................... 40

iv © ISO 2020 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 19902:2020(E)

9.2.1 Permanent action 1, G ................................................................................................... 40

9.2.2 Permanent action 2, G ................................................................................................... 40

9.2.3 Variable action 1, Q ........................................................................................................ 40

9.2.4 Variable action 2, Q ........................................................................................................ 41

9.2.5 Unintentional flooding .................................................................................................... 41

9.2.6 Position and range of permanent and variable actions ...................................... 41

9.2.7 Carry down factors............................................................................................................ 41

9.2.8 Representation of actions from topsides .................................................................. 41

9.2.9 Weight control .................................................................................................................... 41

9.3 Extreme metocean actions .............................................................................................................. 42

9.3.1 General .................................................................................................................................. 42

9.3.2 Notation ................................................................................................................................ 42

9.4 Extreme quasi-static action due to wind, waves and current (E ) ................................... 42

9.4.1 Procedure for determining E ...................................................................................... 42

9.4.2 Direction of extreme wind, waves and current ...................................................... 43

9.4.3 Extreme global actions .................................................................................................... 44

9.4.4 Extreme local actions and action effects ................................................................... 44

9.4.5 Vortex induced vibrations (VIV) .................................................................................. 45

9.5 Extreme quasi-static action caused by waves only (E ) or by waves and

currents (E ) ................................................................................................................................... 45

wce

9.5.1 Procedure for determining E and E ............................................................... 45

we wce

9.5.2 Models for hydrodynamic actions ............................................................................... 46

9.5.3 Hydrodynamic models for appurtenances .............................................................. 50

9.6 Actions caused by current ............................................................................................................... 50

9.7 Actions caused by wind .................................................................................................................... 51

9.7.1 General .................................................................................................................................. 51

9.7.2 Determining actions caused by wind ......................................................................... 51

9.7.3 Wind actions determined from models .................................................................... 52

9.8 Equivalent quasi-static action representing dynamic response caused by

extreme wave conditions ................................................................................................................ 52

9.8.1 General .................................................................................................................................. 52

9.8.2 Equivalent quasi-static action (D ) representing the dynamic response ..... 53

9.8.3 Global dynamic analysis in waves ............................................................................... 53

9.9 Factored actions ................................................................................................................................. 55

9.9.1 General .................................................................................................................................. 55

9.9.2 Factored permanent and variable actions ............................................................... 55

9.9.3 Factored extreme metocean action ............................................................................ 55

9.10 Design situations ................................................................................................................................ 56

9.10.1 General considerations on the ultimate limit state .............................................. 56

9.10.2 Demonstrating sufficient RSR under metocean actions ...................................... 56

9.10.3 Partial factor design format .......................................................................................... 57

9.11 Local hydrodynamic actions .......................................................................................................... 58

10 Accidental and abnormal situations ......................................................................................................... 59

10.1 General ................................................................................................................................................... 59

10.1.1 Treatment of ALS events ................................................................................................. 59

10.1.2 Accidental events .............................................................................................................. 60

10.1.3 Abnormal environmental events ................................................................................. 60

10.2 Vessel collisions .................................................................................................................................. 60

10.2.1 General .................................................................................................................................. 60

10.2.2 Collision events .................................................................................................................. 61

10.2.3 Collision process ................................................................................................................ 61

© ISO 2020 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO 19902:2020(E)

10.3 Dropped objects ................................................................................................................................. 61

10.4 Fires and explosions ......................................................................................................................... 62

10.5 Abnormal environmental actions ................................................................................................ 62

10.6 Assessment of structures following damage ........................................................................... 63

11 Seismic design considerations ................................................................................................................... 63

11.1 General .................................................................................................................................................. 63

11.2 Seismic design procedure ............................................................................................................... 63

11.3 Seismic reserve capacity factor .................................................................................................... 64

11.4 Recommendations for ductile design ......................................................................................... 64

11.5 ELE requirements .............................................................................................................................. 66

11.5.1 Partial action factors ....................................................................................................... 66

11.5.2 ELE structural and foundation modelling ................................................................ 66

11.6 ALE requirements .............................................................................................................................. 67

11.6.1 General ................................................................................................................................. 67

11.6.2 ALE structural and foundation modelling................................................................ 68

11.6.3 Non-linear static pushover analysis ........................................................................... 68

11.6.4 Time-history analysis ...................................................................................................... 70

12 Structural modelling and analysis ............................................................................................................ 70

12.1 Purpose of analysis ........................................................................................................................... 70

12.2 Analysis principles ............................................................................................................................ 71

12.2.1 Extent of analysis .............................................................................................................. 71

12.2.2 Calculation methods ........................................................................................................ 71

12.3 Modelling .............................................................................................................................................. 71

12.3.1 General ................................................................................................................................. 71

12.3.2 Level of accuracy ............................................................................................................... 71

12.3.3 Geometrical definition for framed structures ........................................................ 72

12.3.4 Modelling of material properties ................................................................................ 75

12.3.5 Topsides structure modelling ...................................................................................... 75

12.3.6 Appurtenances ................................................................................................................... 75

12.3.7 Soil-structure interaction .............................................................................................. 76

12.3.8 Other support conditions ............................................................................................... 77

12.3.9 Local analysis structural models ................................................................................. 77

12.3.10 Actions .................................................................................................................................. 78

12.3.11 Mass simulation ................................................................................................................. 78

12.3.12 Damping ............................................................................................................................... 79

12.4 Analysis requirements ..................................................................................................................... 79

12.4.1 General ................................................................................................................................. 79

12.4.2 Fabrication .......................................................................................................................... 81

12.4.3 Other pre-service and removal situations ............................................................... 81

12.4.4 In-place situations ............................................................................................................ 84

12.5 Types of analysis ................................................................................................................................ 86

12.5.1 Natural frequency analysis ............................................................................................ 86

12.5.2 Dynamically responding structures ........................................................................... 86

12.5.3 Static and quasi-static linear analysis ....................................................................... 86

12.5.4 Static ultimate strength analysis ................................................................................. 87

12.5.5 Dynamic linear analysis ................................................................................................. 87

12.5.6 Dynamic ultimate strength analysis .......................................................................... 87

12.6 Non-linear analysis ........................................................................................................................... 88

12.6.1 General ................................................................................................................................. 88

12.6.2 Geometry modelling ........................................................................................................ 88

12.6.3 Component strength ........................................................................................................ 89

12.6.4 Models for member strength ........................................................................................ 89

12.6.5 Models for joint strength ................................................................................................ 89

vi © ISO 2020 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 19902:2020(E)

12.6.6 Ductility limits .................................................................................................................... 89

12.6.7 Yield strength of structural steel ................................................................................. 90

12.6.8 Models for foundation strength ....................................................................

...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 19902
ISO/TC 67/SC 7
Petroleum and natural gas
Secretariat: BSI
industries — Fixed steel offshore
Voting begins on:
2020­03­20 structures
Voting terminates on:
Industries du pétrole et du gaz naturel — Structures en mer fixes
2020­05­15
en acier
ISO/CEN PARALLEL PROCESSING
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 19902:2020(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO 2020
---------------------- Page: 1 ----------------------
ISO/FDIS 19902:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH­1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 19902:2020(E)
Contents Page

Foreword ....................................................................................................................................................................... xiv

Introduction ................................................................................................................................................................ xvii

1 Scope .................................................................................................................................................................... 1

2 Normative references .................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................... 2

4 Symbols ............................................................................................................................................................ 10

5 Abbreviated terms ....................................................................................................................................... 14

6 Overall considerations................................................................................................................................ 16

6.1 Types of fixed steel offshore structure ................................................................................................. 16

6.1.1 General ............................................................................................................................................................. 16

6.1.2 Jackets ............................................................................................................................................................... 16

6.1.3 Towers .............................................................................................................................................................. 17

6.1.4 Jack-ups ............................................................................................................................................................ 17

6.2 Planning ........................................................................................................................................................... 18

6.2.1 General ............................................................................................................................................................. 18

6.2.2 Hazards ............................................................................................................................................................. 18

6.2.3 Designing for hazards ................................................................................................................................. 19

6.2.4 Design situations and criteria .................................................................................................................. 19

6.2.5 Design for inspection and maintenance ............................................................................................... 19

6.2.6 Foundations and active geological processes .................................................................................... 20

6.2.7 Regulations ..................................................................................................................................................... 20

6.3 Service and operational considerations ............................................................................................... 20

6.3.1 General considerations .............................................................................................................................. 20

6.3.2 Water depth .................................................................................................................................................... 20

6.3.3 Structural configuration ............................................................................................................................ 20

6.3.4 Access and auxiliary systems ................................................................................................................... 21

6.4 Safety considerations .................................................................................................................................. 21

6.5 Environmental considerations ................................................................................................................ 21

6.5.1 General ............................................................................................................................................................. 21

6.5.2 Selecting design metocean parameters and action factors ........................................................... 22

6.6 Exposure levels .............................................................................................................................................. 22

6.7 Assessment of existing structures .......................................................................................................... 23

6.8 Structure reuse .............................................................................................................................................. 23

7 General design requirements................................................................................................................... 23

7.1 General ............................................................................................................................................................. 23

7.2 Material properties for steel .................................................................................................................... 24

7.3 Incorporating limit states .......................................................................................................................... 24

7.4 Determining design situations ................................................................................................................ 24

7.5 Structural modelling and analysis .......................................................................................................... 25

7.6 Design for pre-service and removal situations .................................................................................. 25

7.7 Design for the in-place situation ............................................................................................................. 25

7.8 Determination of component resistances ........................................................................................... 25

7.8.1 General ............................................................................................................................................................. 25

7.8.2 Physical testing to derive resistances ................................................................................................... 26

7.8.3 Resistances derived from computer simulations validated by physical testing ................... 26

7.8.4 Resistances derived from computer simulations validated against design formulae ........ 26

7.8.5 Resistances derived from unvalidated computer simulations .................................................... 26

7.9 Strength and stability checks ................................................................................................................... 26

7.9.1 Action and resistance factors ................................................................................................................... 26

© ISO 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 19902:2020(E)

7.9.2 Strength and stability equations ............................................................................................................ 26

7.9.3 Unfactored actions ....................................................................................................................................... 27

7.10 Robustness...................................................................................................................................................... 27

7.10.1 General ............................................................................................................................................................. 27

7.10.2 Damage tolerance ........................................................................................................................................ 27

7.11 Reserve strength .......................................................................................................................................... 28

7.11.1 New structures .............................................................................................................................................. 28

7.11.2 Existing structures ....................................................................................................................................... 29

7.12 Indirect actions ............................................................................................................................................. 29

7.13 Structural reliability analysis .................................................................................................................. 29

8 Actions for pre-service and removal situations ................................................................................ 30

8.1 General ............................................................................................................................................................. 30

8.1.1 Coverage .......................................................................................................................................................... 30

8.1.2 Design situations .......................................................................................................................................... 30

8.1.3 Actions .............................................................................................................................................................. 30

8.2 General requirements ................................................................................................................................ 31

8.2.1 Weight control ............................................................................................................................................... 31

8.2.2 Dynamic effects ............................................................................................................................................. 31

8.2.3 Action effects .................................................................................................................................................. 31

8.3 Onshore lifting ............................................................................................................................................... 33

8.3.1 General ............................................................................................................................................................. 33

8.3.2 Dynamic effects ............................................................................................................................................. 33

8.3.3 Effect of tolerances ...................................................................................................................................... 34

8.3.4 Multi-crane lift .............................................................................................................................................. 34

8.3.5 Local factor ..................................................................................................................................................... 34

8.3.6 Member and joint strengths ..................................................................................................................... 35

8.3.7 Lifting attachments ...................................................................................................................................... 35

8.3.8 Slings, shackles and fittings ...................................................................................................................... 36

8.4 Fabrication ..................................................................................................................................................... 36

8.5 Loadout ............................................................................................................................................................ 36

8.5.1 Direct lift.......................................................................................................................................................... 36

8.5.2 Horizontal movement onto vessel ......................................................................................................... 36

8.5.3 Self-floating structures ............................................................................................................................... 37

8.6 Transportation .............................................................................................................................................. 37

8.6.1 General ............................................................................................................................................................. 37

8.6.2 Metocean conditions ................................................................................................................................... 37

8.6.3 Determination of actions ........................................................................................................................... 37

8.6.4 Other considerations .................................................................................................................................. 38

8.7 Installation ..................................................................................................................................................... 38

8.7.1 Lifted structures ........................................................................................................................................... 38

8.7.2 Launched structures ................................................................................................................................... 38

8.7.3 Crane assisted uprighting of structures ............................................................................................... 38

8.7.4 Submergence pressures............................................................................................................................. 38

8.7.5 Member flooding .......................................................................................................................................... 39

8.7.6 Actions on the foundation during installation .................................................................................. 39

9 Actions for in-place situations ................................................................................................................. 39

9.1 General ............................................................................................................................................................. 39

9.2 Permanent actions (G) and variable actions (Q)............................................................................... 40

9.2.1 Permanent action 1, G .............................................................................................................................. 40

9.2.2 Permanent action 2, G .............................................................................................................................. 40

9.2.3 Variable action 1, Q ................................................................................................................................... 40

9.2.4 Variable action 2, Q ................................................................................................................................... 41

iv © ISO 2020 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/FDIS 19902:2020(E)

9.2.5 Unintentional flooding ................................................................................................................................ 41

9.2.6 Position and range of permanent and variable actions .................................................................. 41

9.2.7 Carry down factors ....................................................................................................................................... 41

9.2.8 Representation of actions from topsides ............................................................................................. 41

9.2.9 Weight control ............................................................................................................................................... 41

9.3 Extreme metocean actions ........................................................................................................................ 42

9.3.1 General ............................................................................................................................................................. 42

9.3.2 Notation ............................................................................................................................................................ 42

9.4 Extreme quasi-static action due to wind, waves and current (E ) ............................................. 42

9.4.1 Procedure for determining E ................................................................................................................. 42

9.4.2 Direction of extreme wind, waves and current ................................................................................. 43

9.4.3 Extreme global actions ............................................................................................................................... 44

9.4.4 Extreme local actions and action effects .............................................................................................. 44

9.4.5 Vortex induced vibrations (VIV) ............................................................................................................. 45

9.5 Extreme quasi-static action caused by waves only (E ) or by waves and

currents (E ) ............................................................................................................................................. 45

wce

9.5.1 Procedure for determining E and E .......................................................................................... 45

we wce

9.5.2 Models for hydrodynamic actions .......................................................................................................... 46

9.5.3 Hydrodynamic models for appurtenances .......................................................................................... 50

9.6 Actions caused by current ......................................................................................................................... 50

9.7 Actions caused by wind .............................................................................................................................. 51

9.7.1 General ............................................................................................................................................................. 51

9.7.2 Determining actions caused by wind .................................................................................................... 51

9.7.3 Wind actions determined from models ................................................................................................ 52

9.8 Equivalent quasi-static action representing dynamic response caused by

extreme wave conditions ........................................................................................................................... 52

9.8.1 General ............................................................................................................................................................. 52

9.8.2 Equivalent quasi-static action (D ) representing the dynamic response ................................ 53

9.8.3 Global dynamic analysis in waves .......................................................................................................... 53

9.9 Factored actions ............................................................................................................................................ 55

9.9.1 General ............................................................................................................................................................. 55

9.9.2 Factored permanent and variable actions .......................................................................................... 55

9.9.3 Factored extreme metocean action ........................................................................................................ 55

9.10 Design situations .......................................................................................................................................... 56

9.10.1 General considerations on the ultimate limit state.......................................................................... 56

9.10.2 Demonstrating sufficient RSR under metocean actions ................................................................. 56

9.10.3 Partial factor design format ...................................................................................................................... 57

9.11 Local hydrodynamic actions ..................................................................................................................... 58

10 Accidental and abnormal situations ...................................................................................................... 59

10.1 General ............................................................................................................................................................. 59

10.1.1 Treatment of ALS events ............................................................................................................................ 59

10.1.2 Accidental events .......................................................................................................................................... 60

10.1.3 Abnormal environmental events ............................................................................................................ 60

10.2 Vessel collisions ............................................................................................................................................ 60

10.2.1 General ............................................................................................................................................................. 60

10.2.2 Collision events ............................................................................................................................................. 61

10.2.3 Collision process ........................................................................................................................................... 61

10.3 Dropped objects ............................................................................................................................................ 61

10.4 Fires and explosions .................................................................................................................................... 62

10.5 Abnormal environmental actions ........................................................................................................... 62

10.6 Assessment of structures following damage ...................................................................................... 63

© ISO 2020 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO/FDIS 19902:2020(E)

11 Seismic design considerations ................................................................................................................ 63

11.1 General ............................................................................................................................................................. 63

11.2 Seismic design procedure ......................................................................................................................... 63

11.3 Seismic reserve capacity factor ............................................................................................................... 64

11.4 Recommendations for ductile design ................................................................................................... 64

11.5 ELE requirements ......................................................................................................................................... 66

11.5.1 Partial action factors ................................................................................................................................... 66

11.5.2 ELE structural and foundation modelling ........................................................................................... 66

11.6 ALE requirements ........................................................................................................................................ 67

11.6.1 General ............................................................................................................................................................. 67

11.6.2 ALE structural and foundation modelling ........................................................................................... 68

11.6.3 Non-linear static pushover analysis ...................................................................................................... 68

11.6.4 Time-history analysis ................................................................................................................................. 70

12 Structural modelling and analysis ......................................................................................................... 70

12.1 Purpose of analysis ...................................................................................................................................... 70

12.2 Analysis principles ...................................................................................................................................... 71

12.2.1 Extent of analysis ......................................................................................................................................... 71

12.2.2 Calculation methods .................................................................................................................................... 71

12.3 Modelling ......................................................................................................................................................... 71

12.3.1 General ............................................................................................................................................................. 71

12.3.2 Level of accuracy .......................................................................................................................................... 71

12.3.3 Geometrical definition for framed structures ................................................................................... 72

12.3.4 Modelling of material properties ........................................................................................................... 75

12.3.5 Topsides structure modelling ................................................................................................................. 75

12.3.6 Appurtenances ..........................................................................................

...

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