1. Cris Moen and Ben Schafer AISI COS Meeting February 2009
Provisional ballot: Direct Strength Method for CFS compression members with holes
Cris Moen and Ben Schafer AISI COS Meeting February 2009

2. DSM Holes (3+ years ago…)
Pn = f (Py, Pcre, Pcrd, Pcrl)?
Does f stay
the same?
Explicitly model hole(s)?
Accuracy? Efficiency?
Identification? Just these
modes?
Gross or net, or some combination?

3. Pn = f (Py, Pcre, Pcrd, Pcrl)?
DSM Holes (today)
Pn = f (Py, Pcre, Pcrd, Pcrl)?
Column strength limited to Pynet
Emphasize elastic buckling prediction methods
DSM curves applicable
when elastic buckling
controls, changes needed though in inelastic regime
Suite of approximate methods now available, “Local hole” buckling modes can affect strength

4. DSM Holes (today) Consider three DSM options:
Option 1 - Replace Py with Pynet everywhere
Option 2 - Cap Pnl and Pnd at Pynet
Option 3 - Cap and transition Pnl and Pnd
Assumes net section exists along full length of column, conservative approach, easiest to implement
Places net section strength limit on existing DSM curves, can be unconservative in some cases
Transition from elastic buckling regime to net section cap at “knee” of DSM design curves, most accurate method but also increases work for engineers

5. DSM Holes (Option 1)
Replace Py with Pynet everywhere

6. DSM Holes (Option 1) Replace Py with Pynet everywhere
Note Pynet replaced with Py assumes net section influence over all slenderness ranges

7. DSM Holes (Option 1)

8. DSM Holes (Option 1)

9. DSM Holes (Option 2)
Cap strength at Pynet

10. DSM Holes (Option 2)
Cap strength at Pynet

11. DSM Holes (Option 2)
10%

12. DSM Holes (Option 2)
25%

13. DSM Holes (Option 3)
Cap strength at Pynet
Transition to Pynet

14. DSM Holes (Option 3)
Cap strength at Pynet
Transition to Pynet

15. DSM Holes (Option 3)

16. DSM Holes (Option 3)

17. Experiments
Ortiz-Colberg (1981), Sivakumaran (1987), Miller and Peköz (1994), Abdel-Rahman (1997), Pu et al. (1999), Moen and Schafer (2008)
- All lipped C-sections - 85% stub columns - hhole/h varies from 0.10 to 0.60

18. Simulations All lipped C-sections, variety of short and long columns
Large number of tests, most of them outside of Main Spec dimensional limits
Option 1 – conservative, Option 2 and 3 comparable, Main Spec struggled
All lipped C-sections, variety of short and long columns
- 35 of 99 SSMA cross-sections represented
- hhole/h varies from 0.10 to hole spacing varies from 8 to 24 inches

19. Conclusions Option 1 - Replace Py with Pynet everywhere
Conservative over all slenderness ranges
Easy to implement
Option 2 - Cap Pnl and Pnd at Pynet
Can be unconservative at “knee” of design curve
Option 3 - Cap and transition Pnl and Pnd
Most consistent with observed data trends
Additional effort to implement, use

20. Also worth mentioning
Once DSM Holes is approved, Main Spec distortional buckling design method can be replaced
Should we prequalify hole shapes, sizes in DSM Holes?
Simplified elastic buckling methods could be used to improve Main Spec…
Plate buckling with holes – Section B2, B3, B4 Distortional buckling with holes – C3.4.1, C4.2
Euler buckling with holes – C3.1.2, C4.1
Goal is to incorporate stiffened holes into DSM Holes next…

21. DSM Holes (Option 3)

22. DSM Holes (Option 3)