Extending the Direct Strength Method for Cold-Formed Steel Design to Through-Fastened Simple Span Girts and Purlins with Laterally Unbraced Compression Flanges
Publication: Journal of Structural Engineering
Volume 140, Issue 6
Abstract
A direct-strength method (DSM) prediction approach is introduced and validated for metal building wall and roof systems that are constructed with steel panels through-fastened with screws to girts or purlins. The focus is capacity prediction for simple spans under wind uplift or suction; however, the DSM framework is generally formulated to accommodate gravity loads, continuous spans, standing-seam roofs, and insulated roof and wall systems in the future. System flexural capacity is calculated with the usual DSM approach; global buckling, local-global buckling interaction, and distortional buckling strengths are determined with a finite-strip Eigen-buckling analysis, including a rotational spring that simulates restraint provided by the through-fastened steel panel. The DSM flexural capacity is then reduced with a code-friendly equation consistent with existing standard provisions to account for the additional stress at the intersection of the web and free flange that occurs as the girt or purlin rotates with respect to a suction (uplift) load. A database of 62 simple-span tests was assembled to evaluate the strength prediction accuracy of the proposed DSM approach alongside existing standard provisions. The proposed DSM approach is confirmed to be viable and accurate for simple spans. Modifications to a standard approach are proposed that could improve its accuracy. The R-factor prediction method is accurate for c-section simple spans, unconservative for z-section simple spans, and overall lacks the generality of the other two approaches reported in this paper.
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgments
The writers are grateful to the Metal Building Manufacturers Association (MBMA) and AISI for supporting and guiding the research reported in this paper. The writers offer special thanks to Dr. Lee Shoemaker and Dr. Teoman Peköz for sharing their valuable historical perspectives on girt and purlin research. This paper was written with support from an MBMA faculty fellowship. Dr. Bac Nguyen of the Hadley Group provided valuable comments that improved the manuscript.
References
American Iron, and Steel Institute (AISI). (2007). “North American specification for the design of cold-formed steel structural members.”, Washington, DC.
Douty, R. T. (1962). “A design approach to the strength of laterally unbraced compression flanges.”, Cornell Univ. Engineering Experiment Station, Ithaca, NY.
European Committee for Standardization. (2006). “Eurocode 3: Design of steel structures.”, Brussels, Belgium.
Fisher, J. M. (1996). “Uplift capacity of simple span cee and zee members with through-fastened roof panels.” Final Rep., Metal Building Manufacturers Association (MBMA) 95-01, Cleveland.
Gao, T. (2012a). “Direct strength method for the flexural design of through-fastened metal building roof and wall systems under wind uplift or suction.” Ph.D. thesis, Virginia Tech, Blacksburg, VA.
Gao, T. (2012b). “Supplement to ‘Direct strength method for the flexural design of through-fastened metal building roof and wall systems under wind uplift or suction.’”, Virginia Tech, Blacksburg, VA.
Gao, T., and Moen, C. D. (2011). “Flexural strength of exterior metal building wall assemblies with rigid insulation.”, Virginia Tech, Blacksburg, VA.
Gao, T., and Moen, C. D. (2012a). “Predicting rotational restraint provided to wall girts and roof purlins by through-fastened metal panels.” Thin-Walled Struct., 61(1), 145–153.
Gao, T., and Moen, C. D. (2012b). “Test videos–Flexural strength experiments on exterior metal building wall assemblies with rigid insulation.” 〈http://hdl.handle.net/10919/18714〉 (Sep. 29, 2013).
Gao, T., and Moen, C. D. (2013). “Flexural strength experiments on exterior metal building wall assemblies with rigid insulation.” J. Constr. Steel Res., 81(1), 104–113.
Hancock, G. J., Celeban, M., Healy, C. L., Georgiou, P. N., and Ings, N. L. (1990). “Tests of purlins with screw fastened sheeting under wind uplift.” Proc., Int. Specialty Conf. on Cold-Formed Steel Structures, American Iron and Steel Institute, Washington, DC, 393–419.
LaBoube, R. A. (1983). “Laterally unsupported purlins subjected to uplift.” Rep. Prepared for the Metal Building Manufacturers Association, Cleveland.
LaBoube, R. A. (1986). “Roof panel to purlin connections: Rotational restraint factor.” Proc., Int. Association for Bridge and Structural Engineering (IABSE) Colloquium on Thin-Walled Metal Structures in Buildings, Zurich, Switzerland, IABSE, Zurich, Switzerland.
LaBoube, R. A., and Golovin, M. (1990). “Uplift behavior of purlin systems having discrete braces.” Proc., Int. Specialty Conf. on Cold-Formed Steel Structures, American Iron and Steel Institute, Washington, DC, 381–392.
Lucas, R. M., Al-Bermani, F. G. A., and Kitipornchai, S. (1997). “Modelling of cold-formed purlin sheeting systems. Part 1: Full model.” Thin-Walled Struct., 27(3), 223–243.
Peköz, T., and Soroushian, P. (1982). “Behavior of c- and z-purlins under wind uplift.” Proc., Int. Specialty Conf. on Cold-Formed Steel Structures, American Iron and Steel Institute, Washington, DC.
Perry, D. C., McDonald, J. R., and Saffir, H. S. (1990). “Performance of metal buildings in high winds.” J. Wind Eng. Ind. Aerodyn., 36(2), 985–999.
Rousch, C. J., and Hancock, G. J. (1996). “Purlin-sheeting connection tests.”, School of Civil and Mining Engineering, Univ. of Sydney, Sydney, Australia.
Rousch, C. J., and Hancock, G. J. (1997). “Comparison of tests of bridged and unbridged purlins with a non-linear analysis model.” J. Constr. Steel Res., 41(2–3), 197–220.
Schafer, B. W., and Adany, S. (2006). “Buckling analysis of cold-formed steel members using CUFSM: Conventional and constrained finite strip methods.” Proc., Int. Specialty Conf. on Cold-Formed Steel Structures, American Iron and Steel Institute, Washington, DC, 39–54.
Seely, F. B., Putnam, W. J., and Schwalbe, W. L. (1930). “The torsional effect of transverse bending loads on channel beams.”, Engineering Experiment Station, Univ. of Illinois, Urbana, IL.
Standards Australia (SA). (2005). “Australian/New Zealand standard: Cold-formed steel structures.”, Canberra, Australia.
Vieira, L. C. M., Malite, M., and Schafer, B. W. (2010). “Simplified models for cross-section stress demands on c-section purlins in uplift.” Thin-Walled Struct., 48(1), 33–41.
Winter, G., Lansing, W., and McCalley, R. B. (1949). “Performance of laterally loaded channel beams.” Vol. 2, Engineering structures supplement, Colston papers, Wiley, New York, 179–190.
Zetlin, L., and Winter, G. (1955). “Unsymmetrical bending of beams with and without lateral bracing.” ASCE Proc., Reston, VA, 81, 774-1–774-20.
Information & Authors
Information
Published In
Journal of Structural Engineering
Volume 140 • Issue 6 • June 2014
Copyright
© 2014 American Society of Civil Engineers.
History
Received: Jun 29, 2012
Accepted: Apr 30, 2013
Published online: May 2, 2013
Published in print: Jun 1, 2014
Discussion open until: Jul 14, 2014
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.