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

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

3. Background
Local buckling and distortional buckling are not distinguishedin current specifications

4. Local buckling tests

5. Testing setup

6. Range of tested specimens

7. Experiments on restraint detail
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 screws on both sides of raised corrugation 
8.5Z073-4E3W
0.96
paired panel-to-purlin screws on both sides of raised corrugation
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 test D11.5Z092-3E4W

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.
25% Imperfection
P25%= lbs (102.5% of test)
Real test
Ptest= lbs
75% Imperfection
P75%= 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

19. Acknowledgments Sponsors People 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

20. Finite strip and LB vs. DB

21. 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

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

23. 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.