JHU Experiments on Braced Thin-Walled Cold- Formed Steel C and Z Beams in Flexure

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Geoffrey Ellis
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1 Experiments on Braced Thin-Walled Cold- Formed Steel C and Z Beams in Flexure Ben Schafer Asst. Professor The Johns Hopkins University June 2001

2 acknowledgments Sponsors AISI and MBMA CECO Buildings, VP Buildings, Clark Steel People Cheng Yu - graduate RA Sam Phillips - undergraduate RA Liakos Ariston - undergraduate RA Jack Spangler - technician Chuck Pearson - Prosser Steel

3 Background Objective Setup Typical results Influence of details Preliminary results Continuing work overview

4 background / motivation Effective width of a web of a cold-formed steel beam? Unification of design? North American Specification American (AISI) vs. Canadian (S136) method AISI expressions inconsistent and discontinuous AISI predicted strength > S136 predicted strength Industry skeptical of academic test data showing problems with AISI predicted strength Definitive testing needed

5 plate buckling coefficient for the flange k f local buckling with web/flange interaction ξ = 3 ξ = 2, pure bending ξ = 1.4 ξ = ratio of web height to flange width (h/b) ξ = 3 ξ = 2 ξ = 1.4 ξ = 1 local buckling finite strip analysis

6 objective New tests are needed to provide direction for the Specification and definitively determine the role of local web/flange interaction for the web effective width Requirements Simple repeatable tests on industry C s and Z s Account for issues in practice related to local buckling of these members, such as attachment to sheeting Focus on local buckling limit states leave distortional and lateral buckling issues for later

7 testing matrix Dimensions: h, b, d, t. Isolation of h/t variation sought MBMA Z s (purlins): h,b,d, fixed, t varied SSMA C s (studs, joists): b,d fixed, h and t varied h/t h/b b/t d/t d/b Tests to be performed num min max min max min max min max min max bracing configuration 3 Z: h,b,~d fixed, t varied same Z: h,b,~d fixed, t varied same C: h,b,d fixed, t varied same same C: b,d,t fixed, h varied same 12 same 0.31 same miscellaneous 4 TOTAL

8 members

9 testing setup standard decking fastened through flanges of purlins to retard lateral and distortional buckling. fastener patterns and spacing investigated. spreader beam to apply the load at 1/3 points tubes at ends and at support points bolting the two specimens together, top of tube flush with top of purlin to avoid crippling at loading point. 1 1/4 x 1 1/4 x angles connecting tension flanges of 2 specimens to insure they act as a unit 12 on center 4x4x1/4 angles bolted to end plates and specimens to avoid crippling at ends. each span is 5 4 on center. Length is selected considering: shear demands, actuator capacity, actuator stroke, and future testing (dist. buckling when panel is removed)

10 overall view

11 typical failure mechanism

12 typical online results

13 elastic buckling modes local ½λ ~ 5 in. distortional ½λ ~ 20 in.

14 elastic buckling 1.70 h=8.5 in. b=2.5 in. d=0.8 to 1.0 in. t=0.059 in. to in. f y =60 ksi M/M y Local Elastic Distortional Elastic web slenderness (h/t)

15 continuous spring analysis (finite strip)

16 fe (elastic) model to develop detail

17 distortional predicted as lowest eigenmode (single screw pattern, t=0.073 in.) panels removed for visual purposes only

18 influence of details

19 local predicted as lowest eigenmode (paired screw pattern, t=0.073 in.) panels removed for visual purposes only

influence of details Specimen M test /M y M test /M aisi note 8.5Z073-5E6W 8.5Z073-1E2W 8.5Z073-4E3W 0.78 0.86 single panel-to-purlin screws - 12" o.c. 0.80 0.88 0.

20 influence of details Specimen M test /M y M test /M aisi note 8.5Z073-5E6W 8.5Z073-1E2W 8.5Z073-4E3W single panel-to-purlin screws - 12" o.c single panel-to-purlin screws on both sides of raised corrugation paired panel-to-purlin screws on both sides of raised corrugation 8.5Z073-5E6W 8.5Z073-4E3W

21 prediction of 8.5 in. Z s AISI (1996) direct strength: local direct strength: distortional web slenderness (h/t) M/My

22 prediction of 8.5 in. Z s inelastic reserve capacity M y <M<M p M/M y direct strength: distortional fastener pattern / spacing influence AISI (1996) direct strength: local 0.7 specimens damaged before testing web slenderness (h/t)

23 comments web/flange interaction details ongoing work testing on C s improved monitoring of testing numerical modeling and extension of results refining design methodology future remove panels, allow distortional buckling move away from effective width?

24 Z C detailed testing plan out-to-out-dimensi inner nondimensional ratios studied h b d r θ t E f y h/t h/b b/t d/t d/b (in.) (in.) (in.) (in.) (deg) (in.) (ksi) (ksi) AISI and S136 different

25 typical results

99 paired panel-to-purlin screws on both sides of raised corrugation

26 influence of details Specimen M test /M y M test /M aisi note 8.5Z059-1E2W 8.5Z059-4E3W paired panel-to-purlin screws on both sides of raised corrugation and in pan paired panel-to-purlin screws on both sides of raised corrugation 8.5Z059-1E2W 8.5Z059-4E3W

27 industry vs. academia? h/t b/t d/t h/b d/b min max min max min max min max min max MBMA Z s SSMA members Rack members Elhouar and Murray (1985) Schafer and Peköz (1999) available members experimental data h/b=

JUNE 2003 REVISION. Submitted to: The American Iron and Steel Institute (AISI) Principal Investigator: Ben Schafer Assistant Professor

JUNE 2003 REVISION. Submitted to: The American Iron and Steel Institute (AISI) Principal Investigator: Ben Schafer Assistant Professor JUNE 2003 REVISION DISTORTIONAL BUCKLING OF C AND Z MEMBERS IN BENDING Project Plan for PHASE 2 of TEST VERIFICATION OF THE EFFECT OF STRESS GRADIENT ON WEBS OF CEE AND ZEE SECTIONS Submitted to: The American