© 2011 Bentley Systems, Incorporated                    Accidental Loading
Design Philosophy                                                                     © 2011 Bentley Systems, Incorporated...
Accidental Loading Design                                                                 © 2011 Bentley Systems, Incorpor...
Accidental Loading Design                                                                                         © 2011 B...
Dynamic Inertial Loading                                                                                     © 2011 Bentle...
Geometric and Material Nonlinearities                                                                              © 2011 ...
7      Beam Elements                                                                                      © 2011 Bentley S...
8        Beam Elements                                                                                    © 2011 Bentley S...
9  Beam Elements                                                                           © 2011 Bentley Systems, Incorpo...
10      Plate Elements                                                                                         © 2011 Bent...
11      Yield Criterion                                                                                    © 2011 Bentley ...
12  Local Buckling                                                                 © 2011 Bentley Systems, Incorporated   ...
13  Joint Flexibility                                                                   © 2011 Bentley Systems, Incorporat...
Dynamic-Nonlinear Analysis                                                                © 2011 Bentley Systems, Incorpor...
Ship Impact                                                                                          © 2011 Bentley System...
© 2011 Bentley Systems, Incorporated Ship Impact      Total Impact (Kinetic) Energy:        E = ½ a m V2        m = vessel...
Ship Impact                                                              © 2011 Bentley Systems, Incorporated      Kinetic...
Ship Impact                                                                      © 2011 Bentley Systems, Incorporated     ...
Ship Impact                                                           © 2011 Bentley Systems, Incorporated     Mesh joint ...
Ship Impact                                                                         © 2011 Bentley Systems, Incorporated  ...
Ship Impact                                                                                              © 2011 Bentley Sy...
Ship Impact                                      © 2011 Bentley Systems, Incorporated  Dynamic Response Results           ...
Ship Impact                       © 2011 Bentley Systems, Incorporated  Collapse Results23 | WWW.BENTLEY.COM
Dropped Object                                                                              © 2011 Bentley Systems, Incorp...
Dropped Object                                                      © 2011 Bentley Systems, Incorporated      Total Impact...
Dropped Object                                                           © 2011 Bentley Systems, Incorporated       Dynami...
Dropped Object                                                                       © 2011 Bentley Systems, Incorporated ...
Accidental Loading Design                            © 2011 Bentley Systems, Incorporated   Collapse Results28 | WWW.BENTL...
Blast Analysis                                                       © 2011 Bentley Systems, IncorporatedPrimary objective...
Blast Analysis                                                                                                      © 2011...
Blast Analysis                                                   © 2011 Bentley Systems, Incorporated    Dynamic Response ...
Blast Analysis                              © 2011 Bentley Systems, Incorporated  Dynamic Response Results:32 | WWW.BENTLE...
© 2011 Bentley Systems, Incorporated     Parvinder Jhita     Product Manager - SACS     Bentley Systems Inc     2113 38th ...
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Accidental loading

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Accidental loading

  1. 1. © 2011 Bentley Systems, Incorporated Accidental Loading
  2. 2. Design Philosophy © 2011 Bentley Systems, Incorporated Accidents will happen because they are accidents. Design philosophy is to prevent an accident developing into a catastrophe. • Design to: – Maintain usability of escape ways – Maintain integrity of shelter areas – Maintain global load bearing capacity – Protection of the environment2 | WWW.BENTLEY.COM
  3. 3. Accidental Loading Design © 2011 Bentley Systems, Incorporated Some typical accidental events on offshore structures are : • Ship Impact • Dropped Object • Blast & Fire Loading3 | WWW.BENTLEY.COM
  4. 4. Accidental Loading Design © 2011 Bentley Systems, Incorporated Accidental events generally involve large plastic strains. To analyze and design against accidental events requires software tools capable of predicting: • Dynamic inertial loading * • Geometric non- linearity • Material non- linearity * API RP 2FB recommends the use of dynamic analysis for blast loading4 | WWW.BENTLEY.COM
  5. 5. Dynamic Inertial Loading © 2011 Bentley Systems, Incorporated SACS DYNAMIC RESPONSE MODULE • Allows for linear, quadratic, or cubic interpolation for the time history input. • Variable time step integration procedure. • Time history plots including modal responses, overturning moments, base shear, etc. • Generation of equivalent static loads. • Generation of incremental loads for Elasto/Plastic analysis5 | WWW.BENTLEY.COM
  6. 6. Geometric and Material Nonlinearities © 2011 Bentley Systems, Incorporated • SACS COLLAPSE MODULE • Gradual development of a plastic hinge through the member cross section • Development of plastic hinges anywhere along the length of the member • Local Buckling • Joint Flexibility • Joint Failure • Member Rupture • Pile Plasticity • User defined strain hardening6 | WWW.BENTLEY.COM
  7. 7. 7 Beam Elements © 2011 Bentley Systems, Incorporated • Collapse allows for hinge formation at any point along member length by sub dividing the member into sub-elements (maximum of 20, default is 8) and monitor the stress level at each sub-element. • Not restricted to hinge formation at member end an center – this pre defines the failure mechanism7 | WWW.BENTLEY.COM Collapse
  8. 8. 8 Beam Elements © 2011 Bentley Systems, Incorporated • Collapse predicts the gradual development of plastic hinge through a member cross section by: Dividing the cross-section into sub-areas and monitoring the stress levels in each sub-area. By default tubular cross sections are divided into 12 sub-areas.8 | WWW.BENTLEY.COM Collapse
  9. 9. 9 Beam Elements © 2011 Bentley Systems, Incorporated - Member Cross Section Sub-Areas for different cross sections9 | WWW.BENTLEY.COM Collapse
  10. 10. 10 Plate Elements © 2011 Bentley Systems, Incorporated • Collapse allows plasticity to occur gradually through the plate thickness. • Sub-divide the plate thickness into sub-layers (5).10 | WWW.BENTLEY.COM Collapse
  11. 11. 11 Yield Criterion © 2011 Bentley Systems, Incorporated • Collapse uses Von Mises-Hencky yield Criterion to determine the onset of plasticity.11 | WWW.BENTLEY.COM Collapse
  12. 12. 12 Local Buckling © 2011 Bentley Systems, Incorporated Three methods available to predict local buckling (1) API LRFD (2) Marshall, Gates et el (3) API Bulletin 2U A moment free hinge is inserted at the location of a local buckling point – axial capacity retained12 | WWW.BENTLEY.COM Collapse
  13. 13. 13 Joint Flexibility © 2011 Bentley Systems, Incorporated Joint Flexibility – Distortion of chord cross section due to forces in the brace and chord. Particularly important for old structures where joint cans were not used. Collapse has two methods implemented to predict joint flexibility. These being: (1) Fessler’s Approach (linear) (2) MSL Approach (non-linear)13 | WWW.BENTLEY.COM Collapse
  14. 14. Dynamic-Nonlinear Analysis © 2011 Bentley Systems, Incorporated SACINP (Model File) DYNPAC (Modal Analysis) CLPINP Mode File (partial) Mass File DYRINP DYNAMIC RESPONSE (Force-Time History Analysis) CLPINA DYROCI (full) COLLAPSE (Non-Linear Analysis)14 | WWW.BENTLEY.COM
  15. 15. Ship Impact © 2011 Bentley Systems, Incorporated Impact Design Criterion: • Low Energy (Operational Impact) Jacket bracing designed to survive operational impact (partial yielding at point of impact). • High Energy (Accidental Impact) Jacket legs designed to survive accidental impact. Face and leg Joints to survive accidental impact loading. Jacket bracing allowed to fail – Structure designed to survive loss of brace member. allowed).15 | WWW.BENTLEY.COM
  16. 16. © 2011 Bentley Systems, Incorporated Ship Impact Total Impact (Kinetic) Energy: E = ½ a m V2 m = vessel mass a = added mass coefficient (1.4 – broadside and 1.1 for bow/stern ) V = vessel velocity Gulf of Mexico : m=1000 metric tons V= 0.5 m/s (operational)16 | WWW.BENTLEY.COM
  17. 17. Ship Impact © 2011 Bentley Systems, Incorporated Kinetic Energy Absorbed Through: • Localized plastic deformation (denting) • Overall elasto plastic deformation of member • Fendering devices (if fitted) • Global deformation of platform • Deformation of the ship itself17 | WWW.BENTLEY.COM
  18. 18. Ship Impact © 2011 Bentley Systems, Incorporated Mesh the impacted member to account for local denting.18 | WWW.BENTLEY.COM
  19. 19. Ship Impact © 2011 Bentley Systems, Incorporated Mesh joint to account for local indentation effects19 | WWW.BENTLEY.COM
  20. 20. Ship Impact © 2011 Bentley Systems, Incorporated To account for energy absorbed by ship deformation, use DNV ship indentation curves for 5000 ton vessel impacting a 1.5 m cylinder.20 | WWW.BENTLEY.COM
  21. 21. Ship Impact © 2011 Bentley Systems, Incorporated Dynamic Response Input Added Mass Coefficient. Mass Velocity Direction Distance Impact Joint21 | WWW.BENTLEY.COM
  22. 22. Ship Impact © 2011 Bentley Systems, Incorporated Dynamic Response Results ship structure22 | WWW.BENTLEY.COM
  23. 23. Ship Impact © 2011 Bentley Systems, Incorporated Collapse Results23 | WWW.BENTLEY.COM
  24. 24. Dropped Object © 2011 Bentley Systems, Incorporated Dropped Object Analysis Certain locations such as crane loading and drilling areas are subject to dropped objects. The platform should survive the initial impact from a dropped object and meet the post-impact criteria to survive a one year environmental load in addition to normal operating conditions. Dropped object analysis also required to determine safe lift heights for platform modification/repair to avoid production shutdown which can be costly.24 | WWW.BENTLEY.COM
  25. 25. Dropped Object © 2011 Bentley Systems, Incorporated Total Impact Energy: E = mgh m = mass of object g = gravitational acceleration h = height from which the object is dropped25 | WWW.BENTLEY.COM
  26. 26. Dropped Object © 2011 Bentley Systems, Incorporated Dynamic Response Input Mass Initial Height Impact velocity joint26 | WWW.BENTLEY.COM
  27. 27. Dropped Object © 2011 Bentley Systems, Incorporated Dynamic Response/Collapse Results IMPACT JOINT DISPLACEMENT27 | WWW.BENTLEY.COM
  28. 28. Accidental Loading Design © 2011 Bentley Systems, Incorporated Collapse Results28 | WWW.BENTLEY.COM
  29. 29. Blast Analysis © 2011 Bentley Systems, IncorporatedPrimary objectives for blast resistant design are:• Personnel safety• Controlled Shutdown• Financial Considerations• Environmental considerationsAPI RP 2FB specifications requires a Ductility LevelBlast (DLB) design for low probability, highconsequence extreme events.A DLB design requires a dynamic analysis toaccounts for inertia loading and a largedeflection analysis to account for geometric andmaterial non-linear effects.A DLB design is required for temporary refuge,safe muster areas and escape routes..29 | WWW.BENTLEY.COM
  30. 30. Blast Analysis © 2011 Bentley Systems, Incorporated Blast analysis requires definition of Blast Wave:: Two Types of Blast Waves Shock Wave 1. Sudden pressure rise. - Explosions from materials in liquid or solid form - Extremely energetic vapor Idealized profile cloud explosion Pressure Wave 2. Gradual pressure rise “Design of Blast Resistant Buildings in Petrochemical Facilities”30 | WWW.BENTLEY.COM
  31. 31. Blast Analysis © 2011 Bentley Systems, Incorporated Dynamic Response Input: Time Load SACS Factor Load case31 | WWW.BENTLEY.COM
  32. 32. Blast Analysis © 2011 Bentley Systems, Incorporated Dynamic Response Results:32 | WWW.BENTLEY.COM
  33. 33. © 2011 Bentley Systems, Incorporated Parvinder Jhita Product Manager - SACS Bentley Systems Inc 2113 38th Street Kenner LA 70065 Telephone (504) 443 5481 Parvinder.Jhita@Bentley.com33 | WWW.BENTLEY.COM
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