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Similar to Accidental loading
Similar to Accidental loading (11)
Accidental loading
- 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 environment
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- 3. Accidental Loading Design
© 2011 Bentley Systems, Incorporated
Some typical accidental events on offshore structures are :
• Ship Impact
• Dropped Object
• Blast & Fire Loading
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- 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 loading
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- 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 analysis
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- 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 hardening
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- 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 mechanism
7 | WWW.BENTLEY.COM Collapse
- 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
Beam Elements
© 2011 Bentley Systems, Incorporated
- Member Cross Section Sub-Areas for different cross sections
9 | WWW.BENTLEY.COM Collapse
- 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
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
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 retained
12 | WWW.BENTLEY.COM Collapse
- 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. 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)
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- 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).
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- 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)
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- 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 itself
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- 18. Ship Impact
© 2011 Bentley Systems, Incorporated
Mesh the impacted member to account for local denting.
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- 19. Ship Impact
© 2011 Bentley Systems, Incorporated
Mesh joint to account for local indentation effects
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- 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.
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- 21. Ship Impact
© 2011 Bentley Systems, Incorporated
Dynamic Response Input
Added
Mass
Coefficient.
Mass Velocity Direction Distance Impact Joint
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- 22. Ship Impact
© 2011 Bentley Systems, Incorporated
Dynamic Response Results
ship
structure
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- 23. Ship Impact
© 2011 Bentley Systems, Incorporated
Collapse Results
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- 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.
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- 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 dropped
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- 26. Dropped Object
© 2011 Bentley Systems, Incorporated
Dynamic Response Input
Mass Initial Height Impact
velocity joint
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- 27. Dropped Object
© 2011 Bentley Systems, Incorporated
Dynamic Response/Collapse Results
IMPACT JOINT DISPLACEMENT
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- 29. Blast Analysis
© 2011 Bentley Systems, Incorporated
Primary objectives for blast resistant design are:
• Personnel safety
• Controlled Shutdown
• Financial Considerations
• Environmental considerations
API RP 2FB specifications requires a Ductility Level
Blast (DLB) design for low probability, high
consequence extreme events.
A DLB design requires a dynamic analysis to
accounts for inertia loading and a large
deflection analysis to account for geometric and
material non-linear effects.
A DLB design is required for temporary refuge,
safe muster areas and escape routes..
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- 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”
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- 31. Blast Analysis
© 2011 Bentley Systems, Incorporated
Dynamic Response Input:
Time Load
SACS
Factor
Load case
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- 32. Blast Analysis
© 2011 Bentley Systems, Incorporated
Dynamic Response Results:
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- 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.com
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