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Analysis and Testing of Cold-Formed Steel Beams

Analysis and Testing of Cold-Formed Steel Beams. Cheng Yu Benjamin W. Schafer The Johns Hopkins University 2003. Overview. Background Experiments Local buckling tests Distortional buckling tests Design methods Extensions (FEA) Conclusions. Background. Local buckling tests.

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Analysis and Testing of Cold-Formed Steel Beams

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  1. Analysis and Testing of Cold-Formed Steel Beams Cheng Yu Benjamin W. Schafer The Johns Hopkins University 2003

  2. Overview • Background • Experiments • Local buckling tests • Distortional buckling tests • Design methods • Extensions (FEA) • Conclusions

  3. Background

  4. Local buckling tests

  5. Testing setup

  6. Range of tested specimens

  7. Specimen Mtest/My Mtest/Maisi note 8.5Z073-5E6W 0.78 0.86 single panel-to-purlin screws - 12" o.c. 8.5Z073-1E2W 0.80 0.88 single panel-to-purlin screwson both sides of raised corrugation  8.5Z073-4E3W 0.86 0.96 paired panel-to-purlin screwson both sides of raised corrugation Experiments on restraint detail 8.5Z073-5E6W 8.5Z073-1E2W 8.5Z073-4E3W

  8. Distortional buckling tests

  9. Comparison of buckling shapes Local buckling test 11.5Z092-1E2W Distortional buckling testD11.5Z092-3E4W

  10. Comparison of load-displacement

  11. Comparison with U.S. Design Compared with North American Spec (NAS 2001) prediction 23 local buckling tests, average Mtest/MNAS=1.02 17 distortional buckling tests, average Mtest/MNAS=0.85

  12. Distortional buckling tests only Compared with North American Spec (NAS 2001) prediction

  13. Direct Strength Method vs. tests Local buckling tests Mtest/MDSL=1.03 Distortional buckling tests Mtest/MDSD=1.03* *formulas similar to AS/NZ Spec.

  14. Extensions • Explicit DB check in North American Spec. • Restraint of existing systems? • Moment gradient influence on DB?

  15. Extensions via modeling

  16. FEA result of local buckling test of Z beams h=8.5 in. t=0.12 in. Simulation @ 25% Imperfection P25%=17968.2 lbs (102.5% of test) Real test Ptest=17524.7 lbs Simulation @ 75% Imperfection P75%=16483.8 lbs (94.1% of test)

  17. Conclusion • Tests that explicitly separate local and distortional buckling are necessary for understanding bending strength • Current North American Specifications are adequate only for local buckling limit states • The Direct Strength expressions work well for strength in local and distortional buckling • More work on restraint and influence of moment gradients is needed

  18. Acknowledgments • Sponsors • MBMA and AISI • VP Buildings, Dietrich Design Group and Clark Steel • People • Sam Phillips - undergraduate RA • Tim Ruth - undergraduate RA • Jack Spangler – technician • James Kelley – technician

  19. Finite strip and LB vs. DB

  20. FE (elastic) and LB vs. DB single screw pattern, t=0.073 in. h=8.5 in. Z beam panels removed for visual purposes only paired screw pattern, t=0.073 in. h=8.5 in. Z beam panels removed for visual purposes only

  21. Direct Strength Method Local buckling strength: Distortional buckling strength:

  22. Local collapse mechanisms (a) Collapse of 8.5 in. Z, t=0.073 in. (b) Collapse of 8.5 in. Z, t=0.059 in. (c) Collapse of 8 in. C, t=0.097 in. (d) Collapse of 8 in. C, t=0.043 in.

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