API 4F Design Study: ASD 89 to LRFD 05

Transcription

1 API 4F Design Study: ASD 89 to LRFD 05 Mike Effenberger, P.E Sathish Ramamoorthy, Ph.D., P.E. June, 2013; PN Document No. SES PPT 002,Rev.0 Preliminary subject to QA check

2 Post Presentation Note This presentation was presented at the API Conference in Washington DC in the summer of Shortly before the presentation it was discovered that the SAP2000 conversion program had random errors in the conversion of the effective length values in the converted SAP2000 file. Due to the effective length errors, comparison results might have errors and would provide results that could result in incorrect conclusions. Therefore numerical results have been removed from the presentation. The prior reported errors (2012) in the element numbering system and loads applied to the models were corrected. Also all models have been converted from StruCAD to SAP2000. Presentation provides the format that the results will be reported. Changes or updates to the 2012 presentation are provided in red font. (to show why the presentation has red color for certain items) 2

3 Contents API 4F Work Background Objectives Design Study Methodology Model Details AISC 05 Analysis Specifications DnV Load Factors (New) Rig Design Study Updated 3

4 API 4F API Funded Study Check Effect of Load Factors for Drilling Structures Paper Code Conversion Issues Going From ASD to LRFD Draft Provided Comments Due June 24, 2012 First Study Meeting API 4F Work Group Mark Trevithick (T&T Engineering) Chair Anthony Mannering (Precision Drilling) Marcus McCoo (NOV) Paul Landis (Lee C Moore) Load Factors DnV Load Factors (Replaced ASCE7 Factors (6/2013) Models Received (last): 03/05/2012 Finish Work Date: 4

5 Background API 4F, Specification for Drilling and Well Servicing Structures states requirements and gives recommendations for suitable steel structures for drilling and well servicing operations API 4F specifies the steel structures to be designed in accordance with Allowable Stress Design/Elastic design per AISC API 4F committee is interested in going from the Allowable Stress Design to the latest strength design Allowable Strength Design (ASD)/Load and Resistance Factor Design (LRFD) provision in AISC specification. Latest AISC specification is AISC The 2010 edition supersedes and is an update of the 2005 edition. The 2010 edition is yet to be supported by Computer Programs. It is in draft mode in latest Beta Version. 5

6 Background In the LRFD design methodology, design results are affected by the load factors selected for the individual loads (self weight, hook load, and environmental loads) For building design, load factors and load combinations are specified in ASCE 7, Minimum Design Loads for Buildings and Other Structures The load factors are generally estimated using the statistical data for the individual loads and reliability concepts Statistical data for Hook load is not readily available. Therefore, the load factors given in ASCE 7 05 was initially used for the design study (first case evaluation). The committee changed the load factors to factors based on DnV OS C101. 6

7 Objectives Paper documenting the experience of other codes/specification while changing from ASD89 to ASD05 or LRFD05 methodology Perform design study on six structures (workover, mast, derrick & substructure) designed using the ASD and LRFD design provisions. Hook load was initially considered a live load with a load factor of 1.6 (ASCE 7, First Case Evaluation) Decided by the API 4F work group on 02/22/2012 Load Factors changed by committee on 6/5/2013 using factors based on DnV Load Factors. Hook, Rotary, and Setback changed to Load Factor similar to Dead Load of

8 Methodology Design performed using the Allowable Stress Design/Elastic Design provisions in AISC (ASD89) will be the base case. The structures will be evaluated according to ASD89 and ASD05 / LRFD05 design provisions per AISC specification. The design results between the Elastic design (89) and Strength Design (05) will be compared for evaluation. 8

9 Design Basis AISC 1989 Specification Allowable Stress Design (ASD 89) AISC 2005 Specification Allowable Strength Design (ASD 05) Load and Resistance Factor Design (LRFD 05) 9

10 Rig Analyses Being Performed ASD-89 (StruCAD) Without 1/3 Stress Allowable Increase in Allowable With 1/3 Stress Allowable Increase in Allowable ASD-89 (SAP) Without 1/3 Stress Allowable Increase in Allowable With 1/3 Stress Allowable Increase in Allowable ASD-05- P-Delta AISC ASCE 7(1.6) ASD-05- P-Delta DnV (1.3) LRFD-05 (DnV 1.3) 10

11 Derrick and Mast Models Provided to SES for Design Study Model Name Type Hook Load (kip) No of Lines Set Back (kip) Height (ft) Reference Wind Speed (knots) Operating Unexpected Expected Elevation from Water Line (ft) Rig 1 Mast xxx Rig 2 Mast & Substructure Land Rig Rig 3 Single Derrick xxx Rig 4 Dual Derrick (Aux) (Aux) xxx Rig 5** Workover Mast xxx Land Rig 11 Notes: Analytical models for Rig1 to Rig 4 were developed in StruCAD For Rig 5, Analytical model was developed in STAAD

12 Rig kip Hook Load Mast 12

13 Rig kip Hook Load Mast & Substructure Z X Y 13

14 Rig kip Hook Load Single Derrick Z X Y 14

15 Rig kip Hook Load Dual Derrick 15

16 Rig kip Hook Load Workover Mast 16

17 Software Details SAP2000 Ultimate 16 (2I (Eye) Beta) from Computers and Structures, Inc (CSI) was used for the latest design study. SAP is a integrated software for structural analysis and design P Δ & P Δwith large displacements Buckling analysis Design Codes ASD 89 ASD 05 LRFD 05 LRFD 10 (Later) 17

18 StruCAD to SAP2000 Conversion StruCAD models were imported in SAP. The imported models were compared with the StruCAD models. In general, most of the model features are imported without any issues. However, there are few StruCAD commands/features that are not imported in SAP. These are manually edited in the imported model or using the SPD StruCAD option. SAP technical support and development team were notified about the import issues. 18

19 StruCAD to SAP 2000 Conversion Outstanding issues Effective Length Factors not imported Effective length specified/used in the StruCAD model is entered as Design Overwrites in SAP model. Conversion not fully corrected. Wind Loads/Area Cards are not imported Wind loads are converted to Member and Joint Loads in StruCAD (Using SPD file) and imported in SAP Acceleration Loads Discrepancy in the base reactions for the acceleration loads in the StruCAD and SAP models. Therefore, the acceleration loads are converted to Member/joint loads in StruCAD (Using SPD file) and then imported in SAP 19

20 StruCAD to SAP 2000 Conversion Design issues Cm factor Difference in calculating the Cm factor between StruCAD and SAP (Beta version has special provision to Ignore lateral loads) Brace Spacing StruCAD has option to input the brace spacing for estimating the effective length. SAP does not have an equivalent parameter to modify. 20

21 API 4F Design Study Status Paper Issued as Draft (Close ) Issue to API End of June Rig Evaluation All 5 Models are ready for Evaluation (StruCAD) Converted Rig #5 to StruCAD Removed duplicate elements Removed plate and shell elements Conversion Issue Minor Axis Moment Error Issue (Fixed) Load Card Format Issue (Fixed) Loads generally compare between program results, still possible issues Section property round off Other 21

22 API 4F Design Study Status (Cont) Analysis Issues K Factors Cm Issue Brace Spacing All 5 Rig analyses were performed Results under review DnV Load Factors (Factors selected by Committee ) Next Load Factors (Pending completion of DnV Results) 22

23 Design Basis Allowable Stress Design 89 The imported models were run in SAP and compared with the StruCAD results In general, the member forces are comparable to the StruCAD member forces. For some members, there are discrepancies. Allowable Stress Design (ASD 89) Static linear analysis With 1/3 rd increase in allowable stress for expected and unexpected load case 23

24 Design Basis Allowable Strength Design 05 Allowable Strength Design (ASD 05) Effective length method Second order analysis method (includes p Δ and p δ) Without 1/3 rd increase in allowable for wind load combinations API 4F load combinations Case Design Loading Dead Load Hook Load Rotary Load Setback Load Environmental Loads Condition (%) (%) (%) (%) (%) 1a Operating b Operating 100 TE*100% Expected 100 TE*100% a Unexpected 100 TE*100% b* Unexpected Erection Transportation Note: Load combinations 3b, 4, & 5 for Earthquake loads, Erection, and Transportation, respectively, were not included in this study

25 Design Basis Load and Resistance Factor Design 05 Load and Resistance Factor Design (LRFD 05) Effective length method General second order analysis method (includes p Δ and p δ) Without 1/3 rd increase in allowable for wind load combinations Hook, Rotary, & Setback loads are considered as permanent equipment loads with 1.3 load factors similar to DnV Load Factors Case Design Loading Dead Load Hook Load Rotary Load Setback Load Environmental Loads Condition (%) (%) (%) (%) (%) 1a Operating b Operating 130 TE*130% Expected 130 TE*130% a Unexpected 130 TE*130% b Unexpected Erection Transportation

26 Comparison of Analysis Methods AISC 05 Specification Direct Analysis Method Effective Length Method First Order Analysis Method Specification Reference Appendix 7 Section C.2.2a Section C.2.2b Limits on Applicability No Yes Yes Type of analysis Second Order Second Order First Order Member stiffness Reduced EI and EA Nominal EI and EA Nominal EI and EA Notional lateral load Yes Yes Yes Column effective length K=1 Sidesway buckling analysis K=1 Note: In AISC 10 specification, Direct Analysis is moved to Section C. Effective length and First Order Analysis Methods are moved to Appendix 7 26

27 Comparison of Analysis Methods Direct Analysis Method Effective Length Method First Order Analysis Method Specification Reference Appendix 7 Section C.2.2a Section C.2.2b Limits on Applicability No Yes Yes Type of analysis Second Order Second Order First Order Member stiffness Reduced EI and EA Nominal EI and EA Nominal EI and EA Notional lateral load Yes Yes Yes Column effective length K=1 Sidesway buckling analysis K=1 Not considered in this study 27

28 Effective Length Method Details Effective Length Method Amplified First Order General Second Order Linear Load combination No P Delta K=1 Force effects are amplified by B1 and B2 factor to account for P Delta** Non linear load combination P delta Effective length from StruCAD model (side sway buckling analysis was not performed) Notional lateral load for gravity load combinations is not included 28 ** B1 and B2 factors account for the P δ and P Δ. For the current API 4F study, to study the effect of changes in the specification for member strength, the B1 and B2 factor of 1.0 was used. Comparison of design results between the ASD 05 (First order) and ASD 89 will show the effect of changes in specifications.

29 StruCAD vs SAP2000 Load Comparison Using RIG #4 for comparison Reactions Reactions (X,Y,Z) are generally within 1% 29

30 StruCAD vs SAP2000 Comparison ASD 89 (Green Book) Rig # # Elem. RIG #1 363 RIG #2 924 RIG # RIG # RIG #5 467 StruCAD W/O 1/3 SAP 2000 W/O 1/3 StruCAD W/ 1/3 SAP 2000 W/ 1/3 StruCAD ALL LDCOMB 30

31 COMPARISON OF ANALYSIS RESULTS Dnv Based Load Factors (Committee 6/5/13) SAP2000 Analyses RIG #1 Bootstrap Mast RIG #2 Mast with Substructure RIG #3 Derrick RIG #4 Dual Derrick RIG #5 Guyed Workover ASD 89 W/O 1/3 ASD 89 W/ 1/3 ASD 05 PΔ Factor 1.6 ASD 05 PΔ Factor 1.3 LRFD 05 31

32 Stability Analysis Methods Comparison From AISC Webinar by Louis Geschwinder, Design for Stability using the 2010 Specification 32

33 Contact Information Michael (Mike) Effenberger, Sathish Ramamoorthy, Stress Engineering Services Westfair East Drive Houston, Texas Phone: (281) Fax: (281)