Comparison of AS 3990 and AS 4100 Design Provisions for Application to Bulk Handling Machinery

Transcription

1 Comparison of AS 3990 and AS 4100 Design Provisions for Application to Bulk Handling Machinery Simon Edgar Senior Structural Engineer Structural Integrity Engineering Pty Ltd Slide 1 of 21

2 DISCLAIMER AND COPYRIGHT ACKNOWLEDGEMENT 1. Material presented may be covered by copyright and should not be reproduced without permission. 2. These notes are intended to provide general information only, across a range of matters. They should not be relied or acted upon. 3. The authors, contributors and presenters of these notes do not accept any responsibility whatsoever for any actions or omissions, by any party, arising out of use of these notes or the material presented. Slide 2 of 21

3 BACKGROUND 1. AS is the standard for structural design of continuous bulk handling machinery. 2. AS is currently being revised. 3. Both the 1995 version and the proposed revision of AS offer the designer a choice between limit state design or permissible stress design. 4. Key changes to the proposed revision of AS are the prescription of different (conventional) limit state partial load factors and a change to the minimum permissible stress design safety factors. Slide 3 of 21

4 AGENDA 1. Theoretical comparisons between AS4100 and AS Practical comparisons/case studies for actual machine designs between: a) AS 4100 vs AS 3990, b) AS vs AS Revision 3. Conclusions and Questions Slide 4 of 21

5 AS 4100 vs AS 3990 THEORETICAL COMPARISON APPROACH 1. Desktop comparison of main member strength design provisions of AS 3990 and AS Considers key differences in strength design limitations only. a) No consideration of other theoretical aspects such as stiffness, serviceability, fatigue etc. b) No consideration of practical aspects such as fabrication methods, constructability, steelwork availability, member rationalisation etc. 3. Limit state load factors and ɸ factors set to provide a total theoretical safety factor comparable with the safety factor achieved by compliance with AS Differences are a direct comparison of member stress ratio or member design utilisation expressed as a percentage. Slide 5 of 21

6 AS 4100 vs AS 3990 THEORETICAL COMPARISON BENDING CAPACITY 1. Slenderness limits for slender sections are similar. 2. Section capacity for compact sections: a) Basis of design provisions for compact sections similar, but AS 3990 provisions simplified based on ratio of S/Z ~ 1.1. b) Minimal difference for I-beams with bending about the major axis (S/Z ~ 1.1). c) Possible for ~ 20-40% difference with bending about the minor axis (or for sections where S/Z > 1.1). d) Extreme example - up to 60% difference for tee section. 3. Section capacity for non-compact sections: a) Standards use similar approach. b) Differences are possible due to AS3990 simplifying assumptions. Slide 6 of 21

7 Slenderness Reduction Factor AS 4100 vs AS 3990 THEORETICAL COMPARISON BENDING CAPACITY 4. Bending member capacity: 1.0 a) Capacity based on reference buckling moment for both standards. b) Reference buckling moment differences possible, due to AS 3990 simplifications. c) Additional differences in slenderness reduction factor calculation. d) Practical differences in slenderness reduction factor ~ 10% e) Larger differences possible where reduction factor < F s /F ob (AS3990) or M s /M o (AS4100) AS4100 AS3990 Slide 7 of 21

8 Buckling Reduction Factor AS 4100 vs AS 3990 THEORETICAL COMPARISON COMPRESSION CAPACITY 1. Local plate buckling slenderness limits are similar. 2. Section (yield) capacity for stocky sections are similar. 3. Member buckling capacity: a) Single buckling curve provided for AS b) 5x buckling curves provided for AS c) Extreme differences is the order of 20-25% l/r Ratio AS3990 AS4100 (αb -1.0) AS4100 (αb -0.5) AS4100 (αb 0.0) AS4100 (αb 0.5) AS4100 (αb 1.0) Slide 8 of 21

9 Non-Uniform Stress Reduction Factor AS 4100 vs AS 3990 THEORETICAL COMPARISON TENSION CAPACITY 1. Yield capacity similar for concentrically connected members with no holes. 2. At holes, AS 4100 considers f u where AS 3990 considers f y. Differences vary from 39% (Gr 250 steel) to 9% (Gr 350 steel). 3. Eccentric Connections: a) Both require reduction factor. b) AS 3990 based on proportions of connected vs unconnected. c) AS 4100 simplified for common sections. d) Differences in range of 0-15% UA (~11%) EA (~3%) UA (~9%) AS3990 AS Ratio of Connected Part (A1) / Unconnected Part (A2) Slide 9 of 21

10 Axial Force Utilisation AS 4100 vs AS 3990 THEORETICAL COMPARISON COMBINED ACTIONS 1. Uniaxial bending: a) Generally both standards consider linear addition of utilisations. b) For specific members, AS 4100 provides alternative, less conservative provisions. c) Using less conservative provisions of AS 4100 results in ~ 15% difference for major axis bending. 2. Biaxial bending: a) AS 3990 based on linear addition of utilisations. b) AS 4100 similar, except for specific sections where AS 4100 uses a power law. c) Using power law ~ 20% difference at 100% total utilisation. BIAXIAL BENDING UTILISATION COMPARISON AS 3990 Combined Actions utilisation AS 4100 Combined Actions utilisation ~ 20% Difference Slide 10 of 21

11 APPROACH TO PRACTICAL COMPARISON (CASE STUDY) 1. AS 3990 vs AS 4100 case studies: a) AS 3990 vs AS 4100 using minimum AS requirements. b) AS 3990 vs AS 4100 using AS per common industry practice. c) AS 3990 vs AS 4100 using AS Revision requirements. 2. AS vs AS Revision case studies: a) AS vs AS Revision using limit state design to AS b) AS vs AS Revision using PSD to AS c) AS vs AS Revision using PSD to AS 3990, based on current common industry practice. 3. Comparisons made between: a) Load / Capacity Ratio for the limit state design approach. b) Stress ratios for the permissible stress design approach. Slide 11 of 21

12 APPROACH TO PRACTICAL COMPARISON (CASE STUDY) 4. Some 2100 individual members assessed for 6 actual / existing machine designs. 5. Sample main, additional and special load combinations considered (Generally 6x load combinations per machine). Case Study Machine AS Wind Machine Type Approx. Mass No. Supplier Region No. Members 1 1 Reclaimer 2000t D Stacker 400t D Reclaimer 2000t D Stacker 400t D Shiploader 1000t D Stacker 500t D 380 Slide 12 of 21

13 APPROACH TO PRACTICAL COMPARISON (CASE STUDY) 6. Differences are presented as the magnitude of difference in design utilisation or stress ratio (expressed as a percentage), calculated as: a) For AS 3990 vs AS 4100 comparisons, differences are calculated as: Difference = Member Design Stress AS 3990 Permissible Stress Limit State Design Action AS 4100 Design Capacity Negative results indicate AS 4100 is more conservative than AS b) For AS vs AS Revision Comparisons: Difference = (AS Utilisation ) (AS Revision Utilisation ) Negative results indicate AS Revision is more conservative than AS These comparisons are made to the member capacity limit and not to each other. Slide 13 of 21

14 Mean Difference in Design Utilisation AS 3990 vs AS 4100 PRACTICAL COMPARISON (CASE STUDY) 1. Results for AS 3990 vs AS 4100 comparison of mean differences in utilisation or stress ratio: a) Results for minimum requirements of AS shown. b) Case study machine 2 has maximum differences. c) Case study machine 6 has minimum differences. 5.0% Machine 1 (Mean) 2.5% Machine 2 (Mean) Machine 3 (Mean) 0.0% -2.5% Slide 14 of 21 E I II/1 III/6 III/8 III/10 AS Load Combination Machine 4 (Mean) Machine 5 (Mean) Machine 6 (Mean)

15 AS 3990 vs AS 4100 PRACTICAL COMPARISON (CASE STUDY) 2. Case study machine 2 results (maximum differences in design utilisation or stress ratio): Governing standard: Load Case AS Minimum Requirements Mean Difference Standard Deviation AS Common industry Practice Mean Difference Standard Deviation AS Revision Minimum Requirements Mean Difference Standard Deviation E I II/ III/ III/ III/ Slide 15 of 21

16 AS 3990 vs AS 4100 PRACTICAL COMPARISON (CASE STUDY) 3. Case study machine 6 results (minimum differences in design utilisation or stress ratio): Governing standard: Load Case AS Minimum Requirements Mean Difference Standard Deviation AS Common industry Practice Mean Difference Standard Deviation AS Revision Minimum Requirements Mean Difference Standard Deviation E I II/ III/ III/ III/ Slide 16 of 21

17 Mean Difference in Design Utilisation AS vs AS REVISION PRACTICAL COMPARISON (CASE STUDY) 1. Results for AS vs AS Revision comparison of mean differences in utilisation using the limit state design approach. Proposed AS Revision is slightly more conservative. 0.0% AS Load Combination E I II/1 III/6 III/8 III/10 Machine 1 (Mean) -2.5% Machine 2 (Mean) -5.0% -7.5% -10.0% Differences are small for operational loading (< 3%) Differences for wind while idle (LC III/10), differences ~ 5-10% Machine 3 (Mean) Machine 4 (Mean) Machine 5 (Mean) Machine 6 (Mean) Slide 17 of 21

18 Mean Difference in Stress Ratio AS vs AS REVISION PRACTICAL COMPARISON (CASE STUDY) 2. Results for AS vs AS Revision comparison of mean differences in stress ratio using the permissible stress design approach. Proposed AS Revision slightly more conservative. 0.0% AS Load Combination E I II/1 III/6 III/8 III/10 Machine 1 (Mean) -2.5% Machine 2 (Mean) -5.0% -7.5% -10.0% Slide 18 of 21 Differences are small for all load combinations (< 5%) Machine 3 (Mean) Machine 4 (Mean) Machine 5 (Mean) Machine 6 (Mean)

19 CONCLUSIONS 1. Limit state design vs permissible stress design: a) The theoretical comparisons show potential for large differences in individual member design. b) The theoretical differences amount to little practical difference in overall machine design outcomes for typical case study machines. 2. AS vs AS Revision: a) The revision provides slight increase in safety factor / reliability for both design approaches. b) The slight increase in safety factor / reliability amounts to little practical difference in overall machine design outcomes for typical case study machines. Slide 19 of 21

20 THANK YOU QUESTIONS? Structural Integrity Engineering Pty Ltd Slide 20 of 21