Shear Buckling of Thin-Walled Channel Sections with Complex Stiffened Webs (No. R924)

Abstract

For cold-formed channel section design in shear, the traditional approach has been to investigate shear plate buckling in the web alone. Recently, an improvement in the elastic buckling stress of the whole thin-walled channel section including flanges and lips in pure shear has been demonstrated. For webs with relatively large depth to thickness ratios, the local buckling mode in shear occurs mainly in web. The structural efficiency of such a web can be improved by adding intermediate stiffeners cold-formed longitudinally in the middle of the webs. This report presents numerical buckling analyses implemented by means of the Semi-Analytical Finite Strip Method (SAFSM). The shear signature curve from the SAFSM is used in a design proposal for a newly developed Direct Strength Method (DSM) for shear. The DSM was formally adopted in the North American Design Specification in 2004 and in the Australian/New Zealand Standard for Cold-Formed Steel Structures (AS/NZS 4600:2005) in 2005 as an alternative to the traditional Effective Width Method (EWM). The theory and development of the shear signature curve has been clearly presented and discussed by Hancock and Pham (2011). The objective of this report is to apply this methodology to investigate the effect of web stiffeners on the elastic shear buckling stress by varying the number, shapes and locations of the longitudinal web stiffeners. A series of shear signature curves and corresponding buckling mode shapes are studied in three different cases of web stiffener geometry where the variables are stiffener position and dimensions. The results from the analysis are included to identify local and distortional buckling caused by shear stresses. The explanation of the occurrence or disappearance of the minima of the shear signature curves where local or distortional buckling occur is also discussed.