2.2 peter delphin
TRANSCRIPT
-
8/10/2019 2.2 Peter Delphin
1/32
Considerations for the structuraldesign of wind turbine generatorfootings in accordance with
Australian Standards
Peter Delphin
March 19, 2014
-
8/10/2019 2.2 Peter Delphin
2/32
Introduction
This presentation will give an overview of the use of thefoundation load document for the structural design of windturbine generator (WTG) footings and how it may be adaptedfor use with Australian Standards.
We will look at the following: Building Code of Australia
WTG Foundation Load document
AS1170 Loading Standards
Structural design requirements
WIF Page 2March 28, 2014
-
8/10/2019 2.2 Peter Delphin
3/32
-
8/10/2019 2.2 Peter Delphin
4/32
-
8/10/2019 2.2 Peter Delphin
5/32
Building Code of Australia (BCA)
Annual probabilities of exceedance:
The BCA defines annual probabilities of exceedance forDesign Events for Safety based on the Importance level forthe structure.
For an importance level of 2, the following values areobtained:
Wind 1:500 annual probability of exceedance
Earthquake 1:500 annual probability of exceedance
WIF Page 5March 28, 2014
-
8/10/2019 2.2 Peter Delphin
6/32
WTG Foundation Load Document
-
8/10/2019 2.2 Peter Delphin
7/32
-
8/10/2019 2.2 Peter Delphin
8/32
WTG Foundation Load Document
Wind turbines are classified in accordance with a referencewind speed measured at hub height of the tower.
Vref is a wind speed averaged over 10 minutes
Ve50
is an extreme 3 second gust wind speed with a return period of 50 years
The wind turbulence category A, B or C is also appended to the class where Arepresents high turbulence, B medium and C low.
WIF Page 8March 28, 2014
Wind turbine class I II III
Vref [m/s] 50 42.5 37.5Ve50 [m/s] 70 59.5 52.5
-
8/10/2019 2.2 Peter Delphin
9/32
WTG Foundation Load Document
Design load cases (IEC 61400-1)
WIF Page 9March 28, 2014
Design Situation DLC Wind Conditions
1. Power production 1.1 to 1.5 Vin< Vhub< Vout , Vr
2. Power production plus
occurrence of fault
2.1 to 2.4 Vin< Vhub< Vout , Vr
3. Start up 3.1 to 3.3 Vin< Vhub< Vout , Vr
4. Normal shutdown 4.1 to 4.2 Vin< Vhub< Vout , Vr
5. Emergency shutdown 5.1 Vr
6. Parked (standing still or idling) 6.1 to 6.4 50-year return, 1-year
return
7. Parked and fault conditions 7.1 1-year return
8.Transport, assembly,
maintenance and repair
8.1 to 8.2 Vmaint
-
8/10/2019 2.2 Peter Delphin
10/32
WTG Foundation Load Document
The design loads given in the foundation load document aremultiplied by partial safety factors depending on the limitstate being analysed and the operating condition. The partialsafety factors are defined in IEC 61500-1
WIF Page 10March 28, 2014
Design situation Partial safety factor
Ultimate limit state, Normal and extreme, N 1.35
Ultimate limit state, Abnormal, A 1.1
Ultimate limit state, Transport, erection,
installation and maintenance, T
1.5
Serviceability limit state 1.0
Fatigue limit state 1.0
-
8/10/2019 2.2 Peter Delphin
11/32
WTG Foundation Load Document
Typical presentation of loads at tower base and coordinate system
March 28, 2014WIF Page 11
-
8/10/2019 2.2 Peter Delphin
12/32
AS1170 Loading Standards
-
8/10/2019 2.2 Peter Delphin
13/32
AS1170 Loading
AS1170 specifies general procedures and criteria for thestructural design of buildings or structures in limit stateformat.
The AS1170 standard is made up of 5 parts:
Part 0: General principles Part 1: Permanent, imposed and other actions
Part 2: Wind actions
Part 3: Snow and ice actions
Part 4: Earthquake actions
WIF Page 13March 28, 2014
-
8/10/2019 2.2 Peter Delphin
14/32
AS1170 Loading
Limit states
States beyond which the structure no longer satisfies the designcriteria
Ultimate limit state
States associated with collapse, or other similar forms of structuralfailure
Serviceability limit state
States that correspond to conditions beyond which specifiedservice criteria for a structure are no longer met.
WIF Page 14March 28, 2014
-
8/10/2019 2.2 Peter Delphin
15/32
AS1170 Loading
AS1170.0 specifies combinations of actions for the ultimatelimit states for stability and strength.
Stability:
Stabilising effects Ed,stb= [0.9G]
Destabilising effects Ed,dst= [1.2G, Wu, psicQ]
Strength:
Ed= [1.2G, Wu, psicQ] permanent, wind and imposed action
Ed= [0.9G,Wu] permanent and wind action
Ed= [G, Eu, psieQ] permanent, earthquake and imposed action
WIF Page 15March 28, 2014
-
8/10/2019 2.2 Peter Delphin
16/32
AS1170 Loading
The 50-year return period wind speed at hub height can be calculatedfrom AS1170.2 and compared with the Ve50wind speed based on thewind turbine classification.
The IEC 61400-1 partial safety factor of 1.35 when applied to the 50-yearreturn period characteristic loads from the foundation load document is
equivalent to a wind with a recurrence period of approximately 580 years.This is comparable to the 1:500 BCA requirement
Therefore the factored extreme loads can be substituted for the ultimateloads, Wu, in the AS1170.0 load combinations.
WIF Page 16March 28, 2014
-
8/10/2019 2.2 Peter Delphin
17/32
AS1170 Loading
WTGs are typically located on
hills, ridges and escarpmentstherefore a topographic surveyplan is required to determine thecoefficient, Mtto calculate windspeed at hub height usingAS1170.2
March 28, 2014WIF Page 17
-
8/10/2019 2.2 Peter Delphin
18/32
AS1170 Loading
Wind speed comparison at hub-height:
AS1170.2 V50wind less than or equal to Ve50
Use factored extreme loads from load document
AS1170.2 V50wind greater than Ve50
Factor the DLC cases that use extreme wind by
Do notfactor the production load cases DLC 1 to 5
WIF Page 18March 28, 2014
-
8/10/2019 2.2 Peter Delphin
19/32
AS1170 Loading
Earthquake loadingAS1170.4
May or may not be included in the foundation load document
If not included a separate assessment will need to be carried out by thestructural engineer. The earthquake load should be added to anoperating wind load case since the earthquake will likely trigger sensorsthat shut down the WTG.
A simple dynamic analysis can be carried out to determine earthquake
forces. Knowledge of the tower construction and mass distribution of theWTG is required.
WIF Page 19March 28, 2014
-
8/10/2019 2.2 Peter Delphin
20/32
Structural design
-
8/10/2019 2.2 Peter Delphin
21/32
Structural design
The structural design of the WTG footing requiresconsideration of the following:
- Ultimate limit state
Stability (overturning, sliding)
Ultimate bearing capacity of the foundation Bending and shear capacity of the footing
Transfer of load from tower to footing
- Serviceability limit state
In-service bearing pressures
Footing rotation/settlement
Crack control in concrete (reinforcement stress)
WIF Page 21March 28, 2014
-
8/10/2019 2.2 Peter Delphin
22/32
Structural design
-Fatigue limit state Concrete stress
Steel reinforcement stress
- Other
Dynamic rotational stiffness Durability
WIF Page 22March 28, 2014
-
8/10/2019 2.2 Peter Delphin
23/32
Structural design
Ultimate limit state
- overturning
- sliding
AS1170.0 requirement
- Ed,std >= Ed,dst
i.e. stabilising >= destabilising
March 28, 2014WIF Page 23
-
8/10/2019 2.2 Peter Delphin
24/32
Structural design
Ultimate limit state
- Soil bearing (triangular)
- Recommend at least 50% ofbase of the footing is in contact
with the ground as soilpressure increasesexponentially with increasingoverturning
- Equivalent uniform pressure
using DNV/Riso approach
March 28, 2014WIF Page 24
-
8/10/2019 2.2 Peter Delphin
25/32
Structural design
Ultimate limit state Bending Shear
Punching
Strength calculationscarried out in accordancewith AS3600 ConcreteStructures using loadcombinations:
1.2G+Wu 0.9G+Wu
March 28, 2014WIF Page 25
-
8/10/2019 2.2 Peter Delphin
26/32
Structural design
Serviceability limit state
- no-gapping requirement
- Footing in full contact with theground
- Expected settlement / rotation(geotechnical advice)
- Cracking in concrete reviewedby limiting reinforcement stress
in accordance with AS3600.
- Crack widths can also bedetermined using Eurocode
March 28, 2014WIF Page 26
-
8/10/2019 2.2 Peter Delphin
27/32
Structural design
Fatigue limit state
- AS3600 Concrete Structuresdoes not have any rules forfatigue assessment
-AS5100 Bridge Structures orEurocode EC2 can be used toassess fatigue in concrete andreinforcement
- Damage equivalent loading
simpler to check fatigue.
- Miners method can be used tosum individual stress rangesand damage ratios
March 28, 2014WIF Page 27
-
8/10/2019 2.2 Peter Delphin
28/32
Structural design
Other
- Rotational stiffness
The rotational stiffness of the footingsneeds to be checked to ensure that itis greater than the minimum value
specified in the foundation loaddocument.
This is necessary to avoid thepossibility that resonance could occurwhen the WTG is operating leading to
increased deflections and rocking.
Geotechnical advice required for thedynamic shear modulus of thefounding material
March 28, 2014WIF Page 28
-
8/10/2019 2.2 Peter Delphin
29/32
Structural design
Durability
Concrete cover to reinforcement and concrete compressivestrength are determined to comply with durabilityrequirements of AS 3600 Concrete Structures.
Detailing of the reinforcement should also comply withAS3600 requirements to control cracking due to shrinkageand temperature effects.
WIF Page 29March 28, 2014
-
8/10/2019 2.2 Peter Delphin
30/32
Summary
-
8/10/2019 2.2 Peter Delphin
31/32
Summary
The WTG foundation load document and the IEC partialsafety factors can be used as ultimate loads for footingdesign.
Wind speed at hub height should be checked using
AS1170.2 and compared with IEC turbine classification.Load cases in the foundation load document using theextreme wind may need to be scaled accordingly.
AS3600 in combination with AS5100 or Eurocode EC2 for
fatigue assessment can be used to design reinforcedconcrete WTG footing.
WIF Page 31March 28, 2014
-
8/10/2019 2.2 Peter Delphin
32/32
Thank You