assessment of offshore structures
Post on 02-Jun-2018
235 Views
Preview:
TRANSCRIPT
-
8/10/2019 Assessment of Offshore Structures
1/43
ISO 19901-9
Current developments in
assessment of fixed offshore structDr Ramsay Fraser
Aberdeen,
September 2013
-
8/10/2019 Assessment of Offshore Structures
2/43
ISO & API code development
-
8/10/2019 Assessment of Offshore Structures
3/43
ISO 19900 series
19901-9 SIM
Andrea MangDec 2012
-
8/10/2019 Assessment of Offshore Structures
4/43
ISO 19900 and API RP2xx alignment
Andrea MangDec 2012
-
8/10/2019 Assessment of Offshore Structures
5/43
way forwardsegmentation of API RP2A
Andrea MangDec 2012
-
8/10/2019 Assessment of Offshore Structures
6/43
alignment strategy
19901-9
Andrea MangDec 2012
-
8/10/2019 Assessment of Offshore Structures
7/43
technical challenges
Andrea MangDec 2012
-
8/10/2019 Assessment of Offshore Structures
8/43
reliability levels in API standards
Andrea MangDec 2012
-
8/10/2019 Assessment of Offshore Structures
9/43
19901-9 evaluation, assessment & mitigatio
19902 states...
Prevention and mitigation
measures should be consideredat all stages of the assessment
Process
-
8/10/2019 Assessment of Offshore Structures
10/43
assessment triggersa) Changes from the original design or previous assessment basis, including
1) addition of personnel or facilities such that the platform exposure level is changed to a more onerous level,
2) modification to the facilities such that the magnitude or disposition of the permanent, variable or environmental acstructure are more onerous,
3) more onerous environmental conditions and/or criteria,
4) more onerous component or foundation resistance data and/or criteria,
5) physical changes to the structure's design basis, e.g. excessive scour or subsidence, and
6) inadequate deck height, such that waves associated with previous or new criteria will impact the deck, and provide
action was not previously considered.
7) 20 years after installation (unless it has already been performed)
b) Damage or deterioration of a primary structural component: minor structural damage can be asses
- appropriate local analysis without performing a full assessment; however, cumulative effects of m
damage shall be documented and included in a full assessment, where appropriate.
c) Exceedance of design service life, if either
the fatigue life (including safety factors) is less than the required extended service life, or
degradation of the structure due to corrosion is present, or is likely to occur, within the required
extended service life.
(More guidance on rigid and flexible joints is reqd. plus interpretation of fatigue is required)
-
8/10/2019 Assessment of Offshore Structures
11/43
assessment methods and
consistent reliability
-
8/10/2019 Assessment of Offshore Structures
12/43
ISO 19902assessment methods
1. DLA (Design Level Assessment)Used for design & assessmentuseful to inform how the structure works (and should be recommeChecks extreme and still water (& seismic)
2. RSR (Reserve Strength Ratio)
shall be achieved but needs to be tied to the RP via hazard curveUsed for assessment (can be used for design)Checks extreme (& seismic) but still water check shall also be pe
3. SRA (Structural Reliability Analysis)
can be used for assessment (used in design for calibration)
-
8/10/2019 Assessment of Offshore Structures
13/43
ISO 19902assessment methods
1. DLA (Design Level Assessment)Load factors derived on a weighted basis for components in a Gen
jacket
2. RSR (Reserve Strength Ratio)accounts for system failure mechanism of actual structure
3. SRA (Structural Reliability Analysis)accounts for uncertainty in system capacity in actual structure
-
8/10/2019 Assessment of Offshore Structures
14/43
ISO 19902assessment methods
1. DLA (Design Level Assessment)Load factors derived on a weighted basis for components in a Gen
jacket
2. RSR (Reserve Strength Ratio)accounts for system failure mechanism of actual structure
3. SRA (Structural Reliability Analysis)accounts for uncertainty in system capacity in actual structure
method is
increasingly
specific to the
actual jacket
being
assessed
-
8/10/2019 Assessment of Offshore Structures
15/43
19900 hazard curves
-
8/10/2019 Assessment of Offshore Structures
16/43
reliability of a structure
-
8/10/2019 Assessment of Offshore Structures
17/43
load pdf and exceedance curves
1 1.5 2 2.5
annualprobability
densityp(E/E100
)
E/E100
NW Shelf
North Sea
limit
0
0.002
0.004
0.006
0.008
0.01
1 1.5 2
annualprobabilityofe
xceedanceQ(E/E100
)
E/E100
NW Shelf
North Sea
limit
-
8/10/2019 Assessment of Offshore Structures
18/43
hazard curve slope (resistance uncertainty)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
1 1.2 1.4 1.6 1.8 2 2.2 2.4
annua
lpro
ba
bility
densityp
(E/E
100
)
E/E100
dxxPxpRPPf RL )()(1)(xpL
)(xPR
-
8/10/2019 Assessment of Offshore Structures
19/43
hazard curve slope (resistance uncertainty)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
1 1.2 1.4 1.6 1.8 2 2.2 2.4
annua
lpro
ba
bility
densityp
(E/E
100
)
E/E100
)(xpL
)(1xPR
dxxPxpRPP
iRLif)()(
1
)(2xPR
)(3xPR
-
8/10/2019 Assessment of Offshore Structures
20/43
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
1 1.2 1.4 1.6 1.8 2 2.2 2.4
pL
(E/E
100
)xP
R(E/E
100
)
E/E100
hazard curve slope (resistance uncertainty)
dxxPxpRP
PiRLif
)()(1
)/()/( 100100 1 EEPEEp RL
)/()/( 1002100 EEPEEp RL
)/()/( 1003100 EEPEEp RL
-
8/10/2019 Assessment of Offshore Structures
21/43
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
100 1000 10000 100000
Baseshearnorma
lise
dby
100ye
ar
bases
hear
return period = 1/Pf
Nsea (1 leg) Nsea (4 braces) Nsea (no resistance or load uncertainty)
1
1
fP2
1
fP3
1
fP
hazard curves
-
8/10/2019 Assessment of Offshore Structures
22/43
Example system failure by single leg memb
-
8/10/2019 Assessment of Offshore Structures
23/43
0.730.760.790.820.850.880.910.940.971.001.031.061.091.12
1.151.181.211.241.271.301.331.361.391.421.451.481.511.54
1.571.601.631.661.691.721.75
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
100 1000 10000 100000
Baseshe
arnorma
lise
dby
100y
ear
bases
hear
return period = 1/PfNsea (1 leg) Nsea (4 braces) Nsea (no resistance or load uncerta
GoM (1 leg) GoM (4 braces) GoM (no resistance or load uncerta
1.92
1.85
RP=6500yrs
Pf=1.
5E-4
RP=10000yrs
Pf=1
E-4
RP=19000yrs
Pf=5E-5
RP=30000yrs
Pf=3
E-5
code implicit reliability - RP, RSR & gE
-
8/10/2019 Assessment of Offshore Structures
24/43
consistent reliability across regionsMike Efthymiou 2011
Location Exposure L1 :Manned High Consequence
L2 Category:Not Normally Manned
ERSR E
RSR
Northern NSea 1.40 1 92 1 09 1 50
NWAustralia 1.702 35 1 26 1 72
Gulf of Mexico 1.592 18 1 17 1 60
LocationExposure L1 (GoM) :Manned Evacuated
E RSR
Gulf of Mexico 1.30 1 78
Used only for winter storm
& sudden hurricane criteria
RP 2A 22ndEd achieves this
-
8/10/2019 Assessment of Offshore Structures
25/43
0.0
1.0
2.0
3.0
4.0
5.0
'70 '74 '78 '82 '86 '90 '94 '98Time in years
Designstorml
oad
North Sea
Gulf of Mexico
100 year load
wave load recipe
4.2
3.3
b d t
-
8/10/2019 Assessment of Offshore Structures
26/43
response based metocean (global consistency)
n year returnperiod base
shear (Xn)
n year return
period wave
height (Hn)
associated wave
period for n year return
period wave (Tn)
n year return
period crest
height
associated curre
n year return pe
wave
wave theory (WT) eg Stokes 5th Determinecurrent to give
Xn when used
with WT, Hnand Tn
h d (RSR f i t i d)
-
8/10/2019 Assessment of Offshore Structures
27/43
hazard curves (RSR for given return period)
Most recent pro
hazard curves steeper than p
However, if the
load has reduc
E10000remains
E/
E100
Richard GibsDec 2012
-
8/10/2019 Assessment of Offshore Structures
28/43
-
8/10/2019 Assessment of Offshore Structures
29/43
-
8/10/2019 Assessment of Offshore Structures
30/43
Wave in deck
e treme ater le el
-
8/10/2019 Assessment of Offshore Structures
31/43
extreme water level
EWL = SWL + settlement + tide + surge + wave crest + diffraction
Example of uncertainty in extrapolation of 10 yrs of data to 100 yr & 10,000 yr R
Richard Gibson
SIM conference
Nov 2012
wave in deck guidance (load and approach)
-
8/10/2019 Assessment of Offshore Structures
32/43
wave-in-deck guidance (load and approach)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
100 1000 10000 100000
OverturningMomen
tratio|OTM|/|OTM100|
Return Period (Years)
Jacket
Deck
COV_R=10%,COV_J
=8%,COV_D=35%
Target Capacity
Jacket + Deck
-
8/10/2019 Assessment of Offshore Structures
33/43
capacity calculation
DLA assessment guidance
-
8/10/2019 Assessment of Offshore Structures
34/43
DLA - assessment guidance
Frame Modeling Joint Modeling Foundation Modeling
Primary Framework Joint Eccentricity Structural/Soil Interaction
Secondary Framework Joint Flexibility Pile/Structure Interaction
Deck Structure Grouted Joints P/Y Modifiers for Condu
Pile Connectivity Doubler Plated Joints Pile Failure Simulation
Grouted Piles Cracked Joints
Conductors Ground JointsConductor Connectivity Member Modeling
Conductor Guide Framing Corrosion Allowance
Support Frame/Deck Modelling Grouted Members
Leg Stubs Damaged Members
Buried members
Design Flooded
non linear analysis re assessment guidance
-
8/10/2019 Assessment of Offshore Structures
35/43
non-linear analysis re-assessment guidanceexample of embedding local detailed shell model in global beam mode
local plastic buckling (and tearing)
-
8/10/2019 Assessment of Offshore Structures
36/43
local plastic buckling (and tearing)
geotechnical re assessment guidance
-
8/10/2019 Assessment of Offshore Structures
37/43
geotechnical re-assessment guidance
1. ICP method or NGI method used to determine soil capacity with grea
on physics rather than the empirical relationships previously available(uncertainties) are reduced and reliability analyses becomes feasibleOvery 2007).
2. The above methods use data from ring shear tests and this may requfurther site investigation for older platforms. Also surface roughness oshear apparatus requires careful maintenance and calibration.
3. In addition, the soil capacity should include the effects of soil strengtwith ageing, cyclic degradation due to large storms, pile interaction atcapacity, soil ductility or brittleness (ie pile tip punch through), shallowpresent) and liquefaction (for seismic response).
4. Conductor modellingshall be modelled as structural (with approprmodifier). Potential further assessment with stiffness from internals if
geotechnical re-assessment guidance
-
8/10/2019 Assessment of Offshore Structures
38/43
geotechnical re-assessment guidance
Group A1
Pin A2
Pin A4
Group A5
Group B1
Pin B2Pin B4
Group B5
-20
0
20
40
60
80
100
120
140
-100 0 100 200 300 400 500
PileHeadForce,MN
Pile Head Displacement, mm
Group A5/B5
Group A1
Group B1
Pin Pile A4,B1 and B2
Pin Pile A2
Extreme (100y, L1 Installation) - Foundation Results
Foundations Curves factored down by required FoS (1.25)
B4
seismic time-history re-assessment guidanc
-
8/10/2019 Assessment of Offshore Structures
39/43
seismic time-history re-assessment guidanc
seismic time-history re-assessment guidanc
-
8/10/2019 Assessment of Offshore Structures
40/43
seismic time history re assessment guidanc
Example snap shot of seismic time history
-
8/10/2019 Assessment of Offshore Structures
41/43
Example snap shot of seismic time history
assessment conditions some questions
-
8/10/2019 Assessment of Offshore Structures
42/43
assessment conditions some questions
Extreme storm conditions
omni-directional 100-year or directional 800-year
(design or assessment)? consistent approach to wave-in-deck
(review existing approach & perhaps clarify from API WID JIP?)
Still water (dead load dominated structures)
Is the operating condition required?
ALE seismic
2500-year but attempt to demonstrate 10,000 load or Pf
-
8/10/2019 Assessment of Offshore Structures
43/43
ISO 19901-9
Current developments inassessment of fixed offshore struct
QUESTIONS
top related