3 - Structural Integrity Evaluation of Offshore Wind Turbines - Giuliani

Structural Integrity Evaluation of Offshore Wind Turbines
Luisa Giuliani Franco Bontempi
luisa.giuliani@uniroma1.it franco.bontempi@uniroma1.it
Structural and Geotechnical Engineering Department
University of Rome “La Sapienza”

Presentation outlineEARTH&SPACE 2010
STRUCTURAL INTEGRITY OF OFFSHORE WIND TURBINES
What is it and why to care about it
STRATEGIES AND MEASURE OF ACHIEVEMENT
Robustness and vulnerability
A CASE STUDY
Investigation of an offshore turbine response to a ship collision
CONCLUSIONS
Conclusive evaluations on application and methodology
L. Giuliani, F. Bontempi - Structural Integrity Evaluation of Offshore Wind Turbines 2/26
A CASE STUDY
STRATEGIES AND MEASURE OF ACHIEVEMENT
CONCLUSIONS
STRUCTURAL INTEGRITY OF OFFSHORE WIND TURBINES

Why care about structural integrity?EARTH&SPACE 2010
MIDDELGRUNDENS VINDMØLLELAUG
Offshore wind farm in Øresund, outside Copenhagen harbor, 2000)
Operator: Dong Energy
Owner: 50% investor cooperative
50% municipality
Official website: http://www.middelgrunden.dk

L. Giuliani, F. Bontempi - Structural Integrity Evaluation of Offshore Wind Turbines
Why care about structural integrity?
4/26
EARTH&SPACE 2010
RUNAWAY EVENT
(Jutland, 2008)
1. High wind and breaking system failure 2. Blades spin out of control and fail
3. Blade debris collided with the tower4. Turbine tower collapses to the ground.

Why care about structural integrity?EARTH&SPACE 2010
RUNAWAY EVENT
(Jutland, 2008)
1. High wind and breaking system failure 2. Blades spin out of control and fail
3. Blade debris collided with the tower4. Turbine tower collapses to the ground.
DISPROPORTION BETWEEN
CAUSE AND EFFECT

Disproportionate collapse in standardsEARTH&SPACE 2010
ASCE 7ASCE 7--02, 200202, 2002
The structural system shall be able to
sustain local damage or failure with the
overall structure remaining stable and not
be damaged to an extend disproportionate
to the original local damage
GSA guidelines, 2003GSA guidelines, 2003
the building must withstand as a minimum,
the loss of one primary vertical load-bearing
member without causing progressive
collapse
Unified facilities criteriaUnified facilities criteria
UFC 4UFC 4--023023--03, DoD 200503, DoD 2005
All new and existing buildings with three
stories or more in height must be designed
to avoid progressive collapse
Model code 1990Model code 1990
Structures should withstand accidental
circumstance without damage disproportionate
to the original events (insensitivity requirement)
ISO/FDIS 2394, 1998ISO/FDIS 2394, 1998
Structures and structural elements should
satisfy, with proper levels of reliability:
-exercise ultimate state requirements
- load ultimate state requirements
- structural integrity state requirements
EN 1991EN 1991--11--7:20067:2006
Structures should be able to withstand
accidental actions (fires, explosions, impacts) or
consequences of human errors, without
suffering damages disproportionate to the
triggering causes
CODESAMERICAN EUROPEAN

Structural integrityEARTH&SPACE 2010
STIFFNESS
Service limit
states (SLS)
RESISTANCE
STRUCTURALSAFETY
Ultimate limit
states (ULS)
SECTIONSSECTIONS
OR ELEMENTSOR ELEMENTS
?
R > S
f < ff < fadmadm
RESISTANCE
TO
EXCEPTIONAL
ACTION
Structural
integrity limit
state (SILS)
STRUCTURAL
SYSTEM
verification on
FAILURE IS PREVENTED
FAILURE IS PRESUMED

OFFSHORE STANDARD, DNVOFFSHORE STANDARD, DNV--OSOS--J101, 2004J101, 2004
The structural system shall be able to resists accidental loads and
maintain integrity and performance of the structure due to local damage
or flooding.
CONSIDERED LIMIT STATESCONSIDERED LIMIT STATES
ACCIDENTAL ACTIONSACCIDENTAL ACTIONS
Structural integrity for OWTEARTH&SPACE 2010
ULS
Ultimate Limit
States
ALS
Accidental Limit
States
FLS
Fatigue Limit
States
SLS
Serviceability
Limit States
maximum load
carrying resistance
failure due to the
effect of cyclic
loading
damage to
components due to
an accidental event
tolerance criteria
applicable to normal
use

STRUCTURAL INTEGRITY OF WIND TURBINE
STRATEGIES AND MEASURE OF ACHIEVMENT
A CASE STUDY
CONCLUSIONS

Different factors affecting structural integrityEARTH&SPACE 2010
P(F) = P(D|H) P(F|DH)P(H) x x
occurrence
of collapse
VULNERABILITY ROBUSTNESSEXPOSURE VULNERABILITY ROBUSTNESSEXPOSURE
[Faber,2006]
[Ellingwood,1983]
STRUCTURALNON STRUCTURAL
MEASURES
avoid dispropor. collapselimit initial damageevent control
2) reduce
the effects of the
action
3) reduce
the effects of a
failure
1) reduce
the action
damage is caused in
the structure
critical event occurs
near the structure
damage spreads in
the structure

EVENT CONTROL
Non structural measuresEARTH&SPACE 2010
Malfunctioning and fire
Natural actions
Ship collision
Malevolent attack
System control
Protective barriers
Sacrificial structures
Surveillance
a. Difficult to prevent every possible accidental event
b. Difficult to protect WT (exposed to natural action)
c. Difficult to surveille WT (wide and isolated area)
reduce the occurrence
of the action
reduce the exposure
of the structure
1)1) REDUCE THE ACTIONREDUCE THE ACTION

Structural measuresEARTH&SPACE 2010
T
O
P
D
O
W
N
Identification of failures at meso-level
(intermediate components)
Identification of failures at micro level
(basic components)
B
O
T
T
O
M
U
P
Deductive (top-down):
critical event is modeled
Inductive (bottom-up):
critical event is irrelevant
ROBUSTNESS
2) REDUCE THE EFFECTS2) REDUCE THE EFFECTS
OF THE ACTIONOF THE ACTION
3) REDUCE THE EFFECTS3) REDUCE THE EFFECTS
OF A FAILUREOF A FAILURE
VULNERABILITY
SHIP COLLISION DAMAGED COMPONENTS

d
)d(R
I
∆
∆
=
Structural robustnessEARTH&SPACE 2010
structure B
d
P
s
STRUCTURE B:
P
s
ROBUSTNESS CURVES
P (performance)
structure A
STRUCTURE A
damaged
integer
∆P
damaged
more performant, less resistant
integer
(damage level)
∆P∆P
more performant, less robust less performant, more robust
PERFORMANCE
ultimate resistance
DAMAGE LEVEL
# removed elements
STRUCTURAL ROBUSTNESS: Insensitivity to local failure
(ASCE/SEI-PCSGC, 2007 – Betonkalender, 2008)
Proposed robustness measure:
decrement of resistance that corresponds
to an increment of damage in the structure

EARTH&SPACE 2010
28
0 1 2 --- 8 d
λ
Exact maxima and minima curves
EXHAUSTIVE INVESTIGATIONEXHAUSTIVE INVESTIGATION
1
Cd
EX.
81
Exhaustive combinations
Cd =
E!
d! × (E-d)!
Ctot = Σd Cd = 2E
0
for D = E
D
a structure of 8 elements is considered as example
Robustness curves

EARTH&SPACE 2010
0 1 2 --- 8 d
Approximated maxima and minima curves
HEURISTIC OPTIMIZATIONHEURISTIC OPTIMIZATION
ERROR!
(non cons.)
14 2
Reduced combinations
= 1
d>1
Cd =
= 2 ×[E-(d-1)]
= E
d=1
d=0
0
D
Ctot = Σd Cd = E2 + 1
for D = E
1
28
Exhaustive combinations
Cd =
E!
d! × (E-d)!
Ctot = Σd Cd = 2E
0
for D = E
D
exponentialexponential
polynomialpolynomial
8
Cd
EX.
Cd
RED.
a structure of 8 elements is considered as example
Robustness curves

8/31
11/31
Stiffbeams(flex.behaviour)Stiffcolumns(shear-type)
STRUCTURALBEHAVIOUR
16 17 18
13 14 15
9 10 121
1
5 6 87
1 2 43
19 20 21
λλλλλλλλgg
16 17 18
13 14 15
9 10 121
1
5 6 87
1 2 43
19 20 21
λλλλλλλλgg
SHEAR-TYPE FRAME ROBUSTNESS
00,51
17 1 2 3 4 5 6 7 8 9 10
Damage Level
PU[ad]
MAX MIN
FLEX-TYPE FRAME ROBUSTNESS
00,250,50,751
0 1 2 3 4 5 6 7 8 9 10
Damage Level
PU[ad]
MAX MIN
λg
5 6 87
9 10 12
13 14 15
16 17 18
19 20 21
41 2 3
11
λg
14
17
1513
18
19
5 6 87
1211
41 2 3
9 10
16
20 21
1 2 43
5 6 87
9 10 1211
13 14 15
16 17 18
19 20 21
λg
λg
14
17
20
1513
1816
2119
5 6 87
41 2 3
9 10 1211
EARTH&SPACE 2010
Comparison between different design solutions

EARTH&SPACE 2010
Robustness applied to OWT
OWT ROBUSTNESS COMPARISON
between two jacket structures between two support types

A CASE STUDY
CONCLUSIONS
A CASE STUDY

EARTH&SPACE 2010
OWT ship collision investigation

EARTH&SPACE 2010
OWTSTRUCTURE MODELING
Pointed mass for
modeling rotor and
nacelle.
One-dimensional elements
for leg and tower with
elastic-plastic behavior
(spread plasticity).
Soil interaction
accounted with 3D
finite elements,
which behave
elastically. Zone
extension calibrated
in order to minimize
boundary effects.
Typical OWT:
5-6 MW power
36 m water depth.
S355 steel monopile with
hollow circular section;
diameter and thickness
vary along the tower.
4 diagonal legs
connected to 4
45 m long
foundation piles,
40 m deepened
into the ground.

EARTH&SPACE 2010
OWTLOAD SCENARIOS SHIP IMPACT MODELING
Only self-weight is assumed to act on
the turbine at the moment of impact.
Three different scenarios are
considered for ship collision point:
A. Impact on one
diagonal leg under
the seabed (model
node #17);
700 ton700 ton
AA

700 ton700 ton
AA
EARTH&SPACE 2010
A. Impact on one
diagonal leg under
the seabed (model
node #17);
B. Impact at the
seabed (model
node #38);
700 ton700 ton
BB

700 ton700 ton
BB
EARTH&SPACE 2010
A. Impact on one
diagonal leg under
the seabed (model
node #17);
B. Impact at the
seabed (model
node #38);
C. Impact on the
tower above the
seabed (model
node #548).
t [s]
F [MN]
0.5 1.5 2.00.0
7
Ship impact is modeled by means
of an impulsive force acting on
the collision point.
The value of the force is 7 MN (ca.
700 ton) and the total length of
the impulsive function is 2 s.
Nonlinear dynamics analyses are
carried on the structure.
700 ton700 ton
CC

EARTH&SPACE 2010
Nonlinear dynamic investigations
SCENARIO A
time: 0.025 s

time: 0.0 s
EARTH&SPACE 2010
SCENARIO A
time: 0.3 s

EARTH&SPACE 2010
SCENARIO A
time: 0.3 stime: 0.5 s

EARTH&SPACE 2010
SCENARIO A

EARTH&SPACE 2010
SCENARIO B
time: 0.0 s

time: 0.0 s
EARTH&SPACE 2010
SCENARIO B
time: 1.0 s

EARTH&SPACE 2010
SCENARIO B

EARTH&SPACE 2010
SCENARIO C
time: 0.0 s

time: 0.0 s
EARTH&SPACE 2010
SCENARIO C
time: 1.0 s

time: 1.0 s
EARTH&SPACE 2010
SCENARIO C
time: 3.0 s

CONCLUSIONS
CONCLUSIONS
A CASE STUDY
A CASE STUDY

SCENARIO EFFECT OF ACTION EFFECT OF DAMAGE
A
Irreversible direct damage of
impacted leg:
VULNERABLE TO ACTION
(not disproportionate, local
resistance may be increased)
Overloading of adjacent legs
and part of monopile,
but no damage propagation:
ROBUST BEHAVIOR
(other damages to be
studied)
B
Elastic deformation:
NOT VULNERABLE TO
CONSIDERED ACTION
---
C
Elastic deformation:
NOT VULNERABLE TO
CONSIDERED ACTION
---
EARTH&SPACE 2010
Nonlinear dynamic investigation results
700 ton700 ton
700 ton700 ton
700 ton700 ton
700 ton700 ton

EARTH&SPACE 2010
FAILURECAUSES TYPES
ACCIDENTAL
ACTIONS
HUMAN ERRORS
§ DESIGN
§ EXECUTION
§ MAINTENANCE
§ IMPACTS
§ COLLISIONS
§ FIRES
UNFAVORABLE
COMBINATIONS
of usual load values or
circumstances:
SWISS CHEESE THEORY
BLADES
§ OVER SPEED
§ FATIGUE FAILURE
§ LOCAL BUCKLING
Handling exceptions of OWT

EARTH&SPACE 2010
FAILURECAUSES TYPES
ACCIDENTAL
ACTIONS
HUMAN ERRORS
§ DESIGN
§ EXECUTION
§ MAINTENANCE
§ IMPACTS
§ COLLISIONS
§ FIRES
UNFAVORABLE
COMBINATIONS
circumstances:
SWISS CHEESE THEORY
BLADES
§ OVER SPEED
§ FATIGUE FAILURE
§ LOCAL BUCKLING
TOWER
§ SHAFT CRACKS
§ WELDING FAILURE
(FATIGUE OR
FAULTY DESIGN)

EARTH&SPACE 2010
FAILURECAUSES TYPES
ACCIDENTAL
ACTIONS
HUMAN ERRORS
§ DESIGN
§ EXECUTION
§ MAINTENANCE
§ IMPACTS
§ COLLISIONS
§ FIRES
UNFAVORABLE
COMBINATIONS
circumstances:
SWISS CHEESE THEORY
BLADES
§ OVER SPEED
§ FATIGUE FAILURE
§ LOCAL BUCKLING
TOWER
§ SHAFT CRACKS
§ WELDING FAILURE
(FATIGUE OR
FAULTY DESIGN)
FOUNDATION
§ MOSTLY FOR OWT
IN CONSTRUCTION

EARTH&SPACE 2010
PreventionPrevention
Indirect design Direct design
Top-down
methods
Bottom-up
methods
Collapse
resistance
Structural
robustness
PresumptionPresumption
Event control
SpecificSpecific
analysesanalyses
StructuralStructural
measuresmeasures performedavoided
CriticalCritical
eventevent modeled
no yes
Invulnerability
Unaccounted
may happen!
No hazards
can occur
Hazards don’t
cause failure
Progressive
collapse
susceptibility
?
Effects areEffects are
uncertainuncertain
?
Behavior followingBehavior following
other hazardsother hazards
remains unknown!remains unknown!
irrelevant
FAULTFAULTFAILUREFAILURE
SECURITYSECURITY INVULNERABILITYINVULNERABILITY

10/31
1 2
S14
32 4
S1
S124
3 4
S2
3
S124
4
S3
2
1
3
4
1
2
3
4
1
4
1
3
1
2
42
3
2
4
3
42
3
2
1 1 1
4
3
42
3
d=0
d=2
d=1
d=3
2
1
3
4d=4
3
4
S123
S1234
4
S134
S13
4
S134
S23
4
S134
S12
4
S4
S0
Computational tree of a
non-deterministic Turing
machine:
all possible configurations
are computed in
polynomial time
(# computational steps s =
# system elements E).
State of acceptance:
damaged
configuration
Initial state:
nominal
configuration
Damaged configurationsEARTH&SPACE 2010

DI1Di1,
D/d
r1
maxI a
i
i
a <<→<<∀





 −
=
EARTH&SPACE 2010
Additional slides
0 1 2 3 4 5 6
d
λ
0 1 2 3 4 5 6
d
λa. Maximum inclination of all the secant lines
that connect the first point of the curves
with the points pertaining to greater
damage levels.

DI1Di1,
D/d
r1
maxI a
i
i
a <<→<<∀





 −
=
EARTH&SPACE 2010
Additional slides
0 1 2 3 4 5 6
d
λ
0 1 2 3 4 5 6
d
λa. Maximum inclination of all the secant lines
damage levels
b. Highest variation of secant lines between
two subsequent points (critical elements
are most relevant)
( ) ( ) Di
2
rrrr
maxI 1iii1i
b <∀





 −−−
= +−
)isostatic(5.0I0)linear( b ≤≤←

DI1Di1,
D/d
r1
maxI a
i
i
a <<→<<∀





 −
=
EARTH&SPACE 2010
Additional slides
c. Area subtended by the curve of minima weighted by the difference between that area and
the area subtended from the curve of maxima (representing the scattering)
a. Maximum inclination of all the secant lines
damage levels
are most relevant)
[ ] [ ]






−⋅+= ∑∑
==
D
0d
LOWUP
D
0d
LOW
c )d(r)d(rk)d(rDI ( ) 1k0for,1D2I5.0 c <<−⋅<≤→
0 1 2 3 4 5 6
d
λ
0 1 2 3 4 5 6
d
λ
( ) ( ) Di
2
rrrr
maxI 1iii1i
b <∀





 −−−
= +−

( ) ( ) Di
2
rrrr
maxI 1iii1i
b <∀





 −−−
= +−
DI1Di1,
D/d
r1
maxI a
i
i
a <<→<<∀





 −
=
EARTH&SPACE 2010
Additional slides
0 1 2 3 4 5 6
d
λ
0 1 2 3 4 5 6
d
λ
damage levels
are most relevant)
d. Scattering from linear trend, calculated as the area subtended between the curves and the
straight line that connect the point of the integer structure with that one of the null one.
[ ] [ ] 2
D
)1k()d(rk)d(rI
D
0d
UP
D
0d
LOW
d ∑∑
==
+−+= EDand1k0for,1I1 d =<<<≤−→
( ) 1k0for,1D2I5.0 c <<−⋅<≤→[ ] [ ]





−⋅+= ∑∑
==
D
0d
LOWUP
D
0d
LOW
c )d(r)d(rk)d(rDI

( ) ( ) Di
2
rrrr
maxI 1iii1i
b <∀





 −−−
= +−
[ ] [ ]






−⋅+= ∑∑
==
D
0d
LOWUP
D
0d
LOW
c )d(r)d(rk)d(rDI ( ) 1k0for,1D2I5.0 c <<−⋅<≤→
[ ] [ ] 2
D
)1k()d(rk)d(rI
D
0d
UP
D
0d
LOW
d ∑∑
==
+−+= EDand1k0for,1I1 d =<<<≤−→
DI1Di1,
D/d
r1
maxI a
i
i
a <<→<<∀





 −
=
EARTH&SPACE 2010
Additional slides
damage levels
are most relevant)
e. Upper and lower bound for maximal damage that makes the structure unstable
UPLOW
e DkDI ⋅+= E2I0and1k0andDDD1 c
UPLOW
≤≤<<≤≤≤←
d. Scattering from linear trend, calculated as the area subtended between the curves and the
straight line that connect the point of the integer structure with that one of the null one.
0 1 2 3 4 5 6
d
λ
0 1 2 3 4 5 6
d
λ
DLOW DUP

EARTH&SPACE 2010
Additional slides
START
d := 0
for e =1 to E
d := 1
NL static analysis λu
0
λu,e
1
Remove element e
Pushover analysis
Restore element e
for d = 2 to D
λu
1
MAX, e1
MAX
λu
1
MIN, e1
MIN
Remove element e(d-1)
MIN
for e =1 to E
λu,e
d
Remove element e
Pushover analysis
Restore element e
CALLCALL ““CURVE MAXCURVE MAX””
CALLCALL ““CURVE MINCURVE MIN””
Robustness quantification
if e <> ed
MIN
λu
d
MIN,
ed
MIN
““CURVE MINCURVE MIN““ MACROMACRO
Curve of minima
END
Restore integer structure
Calculate area or derivativesExtrapolate equations
Calculate corresponding ∆RFix an admitted ∆d
Identify critical elementsSpot abrupt decrement
ROBUSTNESS QUANTIFICATIONROBUSTNESS QUANTIFICATION
ALGORITHM FOR HEURISTIC OPTIMIZATIONALGORITHM FOR HEURISTIC OPTIMIZATION

EARTH&SPACE 2010
Additional slides
Pushover on integer structure
Resulting robustness histogram
Plastic strain development Axial stress development
Meshed elements Plastic moment development
Response curve
Max and min robustness histogramsPlasticization development
ALGORITHM FOR REDUCED ANALYSESALGORITHM FOR REDUCED ANALYSESMax resistance

STAR STRUCTURE ROBUSTNESS
00,51
0 1 2 3 4 5 6 7 8
Damage Level
PU[ad]
MAX MIN
t
d
R
R
Dd
cos25.0max
,...,1
←=






∂
∂
=′
=
EARTH&SPACE 2010
Additional slides
# of elements: E = 8
static indetermin. level: i = 21
lower max. damage: Dmin = 8
upper max. damage: Dmax = 8
fixed max. damage: D = 8
reduced combination: Cred = 65
exhaust. combination: Cex= 256
λλgg
1 2
4
3
5
8
6
7
STATIC INDETERMINANCY:
high restrain grade
Damage
d El. ID Pumin El. ID Pumax
0 0 1 0 1
1 1 0,831745 3 0,896185
2 5 0,648331 7 0,832096
3 4 0,523591 2 0,684849
4 8 0,376882 8 0,580928
5 2 0,269581 6 0,429733
6 6 0,16434 4 0,320632
7 7 0,042504 1 0,261956
8 3 0 5 0
MIN CFG MAX CFG
Ib ≈ 0
Ia ≈ 1
ROBUSTNESS INDICATOR:
( ) ( ) Di
2
rrrr
maxI 1iii1i
b <∀





 −−−
= +− )isostatic(5.0I0)linear( b ≤≤→
Ed0
Ed
)d(r
maxIa ≤≤∀






= )isostatic(EI1 b ≤≤→
Ib maximum slope pt. tangent (measure the abrupt decrement
due to the removal of critical element)
Ia maximum secant starting from the 1st pt. (account for the
lateness of an abrupt decrement)

EARTH&SPACE 2010
Additional slides
λ
15 16 1417
11 9 1210
18 20 1921
13
7 5 3 1 2 4 6 8

TRUSS STRUCTURE ROBUSTNESS
00.250.50.751
0 1 2 3 4 5 6 7 8 9
Damage Level
PU [ad] MAX MIN
EARTH&SPACE 2010
Additional slides
Damage
0 0 1 0 1
1 9 0,471351 1 0,888941
2 3 0 2 0,888941
3 10 0 11 0,628625
4 17 0 12 0,628625
5 16 0 5 0,628625
6 1 0 6 0,628625
7 5 0 13 0,628625
8 11 0 14 0,628625
9 6 0 17 0
MIN CFG MAX CFG
12
1 2
11 5 6 13 14
17
9
3
λ
15 16 1417
11 9 1210
18 20 1921
13
7 5 3 1 2 4 6 8
MAX
1
15 16 14
11 9 1210
18 20 1921
13
7 5 3 2 6 84
17
0,26 > Ib > 0,13
MIN
15 16 1417
11 9 1210
18 20 1921
13
7 5 3 1 2 4 6 8
4,76 > Ia > 1,11

EARTH&SPACE 2010
Additional slides
5
8 6 97
12 10 1311
4 2 31
λ

VIERENDEEL STRUCTUREROBUSTNESS
00,250,50,751
0 1 2 3 4 5 6 7 8 9 10
Damage Level
PU [ad]
MAX MIN
EARTH&SPACE 2010
Additional slides
Damage
0 0 1 0 1
1 6 0,187621 1 0,938097
2 10 0 2 0,625317
3 1 0 3 0,375242
4 2 0 6 0,187621
5 3 0 7 0,187621
6 4 0 8 0,187621
7 5 0 9 0,187621
8 7 0 4 0,187621
9 8 0 5 0,187621
10 9 0 10 0
MIN CFG MAX CFG
6
1
2
3
7 8 9 4 5 10
6
10
5
8 6 97
12 10 1311
4 2 31
λ
MIN
5
8 6 97
12 1311
4 2 31
10
0,31 > Icr > 0,09
MAX
λ
5
8 6 97
12 1311
4 2 31
10
8,12 > Ia > 2,03

TRUSS STRUCTURE ROBUSTNESS
00,250,50,751
0 1 2 3 4 5 6 7 8 9
Damage Level
PU [ad] MAX MIN
EARTH&SPACE 2010
Additional slides
5
8 6 97
12 10 1311
4 2 31
λ
VIERENDEEL STRUCTURE ROBUSTNESS
00,51
0 1 2 3 4 5 6 7 8 9 10
Damage Level
PU [ad] MAX MIN
6
6
1
2
3
7 8 9 4 5 1010
High element connectionHigh element number
14
5 3 1 2 4 6 8
λ
7 5 3 1 2 4 6 8
14
11 9 1210
18 20 1921
13 15 1617
λ
STATIC INDETERMINANCY
i = 4 i = 12
0,26 > Ib > 0,13 0,31 > Ib > 0,09
9
3
12
1 2
11 5 6 13 14
17
8,12 > Ia > 2,034,76 > Ia > 1,11

EARTH&SPACE 2010
Additional slides
3
1
4 2
5 λλgg
STATICINDETERMINANCY
restraint
I3V STRUCTURE ROBUSTNESS
00,51
0 1 2 3 4 5
Damage Level
PU[kN]
MAX MIN
I3C STRUCTURE ROBUSTNESS
00,250,50,751
0 1 2 3 4
Damage LevelPU[kN]
MAX MIN
3
1
2 4
λλgg
connection
14
13 15
16
10
12 11
9
6 5
1 2
7
8
4
3
λλgg
I3E STRUCTURE ROBUSTNESS
00,250,50,751
0 1 2 3 4 5
Damage Level
PU[kN]
MAX MIN
element

EARTH&SPACE 2010
Additional slides
HIGH CONNECTION
Continuity
Compartmentalization
Isolation
Element
number
Element
connection
LOCAL REDUCTION
OF CONTINUITY
LOCAL MECHANISM
DEVELOPMENT
Redundancy
Fragility
LOW CONNECTION
LOCAL REDUCTION OF
DUCTILITY
(inhomogeneous stiffening
of predetermined sections)
EARLY RUPTURE AND
DETACHMENT
Element
ductility
Ductility
External
(restraints)
STRESS IS NOT TRANSMITTED
COLLAPSE
STANDSTILL
STRESS REDISTRIBUTION
HIGH STRESS TRANSMISSION
on adjoining elements after a localized failure
TRIGGERING OF CHAIN
RUPTURE
PROGRESSIVE COLLAPSE
DISPROPORTIONATE COLLAPSE SUSCEPTIBILITY
SUDDEN/EARLY
COLLAPSE
Internal
(constraints)
*
Starossek &
Wolff, 2005*
FEASIBLE ALTERNATE LOAD
PATH
ROBUSTNESS

EARTH&SPACE 2010

L. Giuliani, F. Bontempi - Structural Integrity Evaluation of Offshore Wind Turbines
Why caring for structural integrity?
2
EARTH&SPACE 2010
LILLEGRUND offshore wind farm
(Øresund between Malmö and København, Siemens, June 2008)

3 - Structural Integrity Evaluation of Offshore Wind Turbines - Giuliani

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