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Direct Strength Prediction of Cold-Formed Steel Beam-Columns

Direct Strength Prediction of Cold-Formed Steel Beam-Columns . Y. Shifferaw , B.W. Schafer Research Progress Report to MBMA February 2012. Origins of a different approach. Steel beam-column design (hot-rolled and cold-formed) traditionally follows an interaction equation approach.

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Direct Strength Prediction of Cold-Formed Steel Beam-Columns

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  1. Direct Strength Prediction of Cold-Formed Steel Beam-Columns Y. Shifferaw, B.W. Schafer Research Progress Report to MBMA February 2012

  2. Origins of a different approach • Steel beam-column design (hot-rolled and cold-formed) traditionally follows an interaction equation approach. • The origins of which can be traced back to the much beloved engineering solution to stress in a beam:

  3. Origins of a different approach (cont.) • First yield (for section symmetric about axis of bending) follows this linear interaction:but, basically nothing else! • In CFS design it is presumed that first yield may be replaced by nominal capacity: For CFS recall that these capacities are determined from relatively complex calculations, that we may summarize as.. Py and My might behave, but what about all these “cr”’s, local, distortional and global buckling??

  4. Traditional CFS interaction approach(locally slender example) Py Pn Pcrl Mn My Mcrl

  5. Let’s fire up my favorite tool and explore what stability does under the more complex demands of a beam column

  6. CUFSM

  7. Approx. 8 ZS 225 x 065 (55ksi)

  8. Axial only

  9. Stability under axial only

  10. Restrained bending only

  11. Stability under bending only

  12. Reference stress 0.25Py,0.75My Applied as reference loads 1/3 P/M ratio… 0.25Py 0.75My

  13. Comparing stability solutions Stability does not follow the linear interaction, can be better, worse or same…

  14. P,Mxx,Mzz all at the same time! +0.25MZZy -0.25MZZy

  15. Origins of a different approach (cont.) • Conclusion from this little FSM study is that elastic buckling is dependent on cross-section and on applied demands (P, Mx, Mz) in a nonlinear fashion. • Cross-section stability analysis which picks up this dependency is available. • Standard interaction approach is limited and can not take advantage of situations when stability is favorable, instead always assumes a worst case linear reduction…

  16. Traditional CFS interaction approach(locally slender example) Revisited Py Pn Pcrl Mn My Mcrl

  17. CFS interaction(locally slender example) unsymmetric bending axis.. Py Pn Pcrl Mn My Mcrl

  18. CFS interaction(locally slender example) unsymmetric bending axis.. Py Pn Pcrl Mn My Mcrl How to generalize formulation to take advantage of this, is the research!

  19. Research • Proposal goes back to 2008, solicited from AISI • 2011 MBMA partnered with AISI to help fund the first year of the work • Research is now underway • Long term potential is greater than CFS, but with DSM in AISI-S100 it is the logical starting place

  20. Current Progress

  21. Year 2-3 work (if funded)

  22. Current Progress

  23. Industry assistance • ADTEK (Jeffrey Klaiman), • NUCON1(Rick Haws, Anwar Merchant & BaoPham), • MESCO (Harley Davidson), • BUTLER (Al Harroldand FredericoBueno) • ALPINE (Tamil Samiappan and Bill Babich). and • MBMA (Lee Shoemaker) • AISI (Jay Larson) 1. R.I.P.

  24. Selecting industry relevant beam-columnsTruss

  25. Selecting industry relevant beam-columnsCFS Framing Model buildings from • Devco (CFS-NEES) • Adtek • Nucon CFS-NEES building

  26. Selecting industry relevant beam-columnsMetal building

  27. Focus on Secondary (CFS) members Like eave strut.. and of course purlins and girts

  28. Enjoying learning integrated building design

  29. Identifying key beam-columns… M only P+M d=1.079” t=0.068” 0.25 0.68 0.25 0.68 0.94 0.36 0.36 Combined axial and bending stress index 0.14 0.14

  30. Continuous Eave strut design example LC30=1.0D+0.750L+0.750WPA2 W( 1.0D+0.750L) P=( f(0.750WPA2))

  31. Current Progress

  32. Preliminary formulation Demands set the Pr/Mr ratio of interest, which is the slope of this line! Py Pn by Pcrl bn bcrl Mn My Mcrl

  33. Preliminary formulation (2) For local buckling of a stub section, P or M simply replaced by b! y

  34. Automating CUFSM (P+Mx)

  35. Automating CUFSM (P+Mz)

  36. Current Progress

  37. Selecting industry relevant beam-columnsCFS Framing Model buildings from • Devco (CFS-NEES) • Adtek • Nucon CFS-NEES building

  38. Focusing on most efficient sections Pn/A All CFS framing members Most efficient Mn/A

  39. Selection based on predicted limit states Axial local Bending dist. Axial dist Bending local Axial local Bending yield Axial dist Bending yield Local only! Distortional only! Focus is here in the limited year one work, expansion to more complicated cases in years 2 and 3 if funded Color indicates an efficient section

  40. Modeling • Nonlinear shell FE models of imperfect CFS member • End displacements over desired P, Mx, My • Boundary conditions and lengths to isolate local and distortional buckling • Preliminary models completed with success

  41. P-Mmajor, distortional, C section

  42. P-Mminor, distortional, C section

  43. Potential! Local DSM vs minor axis strength bounds for C

  44. Current Progress

  45. Related Recent Testing (Setup)

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