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Towards a Direct Strength Method for Cold-Formed Steel Beam-Columns

Towards a Direct Strength Method for Cold-Formed Steel Beam-Columns. Structural Stability Research Council Orlando, Florida May 2010 Y.Shifferaw 1 , B.W.Schafer 2 (1),(2) Department of Civil Engineering- Johns Hopkins University. Acknowledgments. National Science Foundation.

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Towards a Direct Strength Method for Cold-Formed Steel Beam-Columns

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  1. Towards a Direct Strength Method for Cold-Formed Steel Beam-Columns Structural Stability Research Council Orlando, Florida May 2010 Y.Shifferaw1 , B.W.Schafer2 (1),(2) Department of Civil Engineering- Johns Hopkins University

  2. Acknowledgments • National Science Foundation

  3. Overview • Introduction • Basis of DSM: yield and elastic critical buckling • Finite element collapse analysis in the P-M space • Direct Strength Method preliminaries for local and distortional buckling in the P-M space • Conclusion • Future research

  4. Postulated b n curve for all P and M ratios Postulated b n curve for all P and M ratios Postulated b for a given P and M ratio Postulated b for a given P and M ratio Py My Introduction • Current and postulated beam-column design approaches

  5. 1.75 in 1.75 in 1 in. 250 1.625 in. 0.5 in. 3.625 in. 6 in. 0.5 in. 1 in. 2 in. 1.625 in. Eave Strut Channel t=0.08in. fy=55.9 ksi Sections considered

  6. DSM basis: major axis yielding and elastic buckling

  7. DSM basis: minor axis yielding and elastic buckling

  8. DSM basis: biaxial yielding and elastic buckling

  9. Finite element modeling • Objective To study combined P-M collapse loads in CFS beam-columns for local and distortional limit states. • Method • Material and geometric nonlinear analysis in ABAQUS using S9R5 shell element models; geometric local and distortional imperfections considered • Models generated from purpose-built Matlab code

  10. Local FE

  11. Major axis local for channel

  12. Major axis local for eave strut

  13. Distortional FE

  14. Minor axis distortional for channel section

  15. Minor axis distortional for eave strut section

  16. Overview • Introduction • Basis of DSM: yield and elastic critical buckling • Finite element collapse analysis in the P-M space • Direct Strength Method preliminaries for local and distortional buckling in the P-M space • Conclusion • Future research

  17. Preliminary DSM beam-column strength prediction LOCAL

  18. Local DSM vs major axis strength bounds for channel

  19. Local DSM vs minor axis strength bounds for channel

  20. Local DSM vs major axis strength bounds for eave

  21. Local DSM vs minor axis strength bounds for eave

  22. Preliminary DSM beam-column strength prediction DISTORTIONAL

  23. Distortional DSM vs major axis strength bounds for channel

  24. Distortional DSM vs minor axis strength bounds for channel

  25. Distortional DSM vs major axis strength bounds for eave

  26. Distortional DSM vs minor axis strength bounds for eave

  27. Conclusion • Under combined loading the assumptions in linear interaction equations are invalidated in CFS members due to • Un-symmetric shapes of common CFS sections • Consideration of cross-section stability • Finite element models for local and distortional models are developed to examine load-bending collapse envelopes. • Preliminary Direct Strength Method design expressions for beam-columns in local and distortional buckling as a function of elastic section slenderness are established and compared with the FE models developed. • Significant efficiency in the proposed DSM approach in comparison with traditional design.

  28. Future work • Incorporation of recently proposed inelastic bending provisions • Further preliminary studies including global buckling • Beam-column tests • Comprehensive FE parametric study • Formal DSM proposals for beam-columns

  29. ?

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