Cold-formed steel curtain wall

A non-load-bearing wind stud, to AISI S240-20 and the AISI S100-16 North American Specification with Supplement S2-20. It covers the stud, its track, and the deflection track at its top, and reports the limiting height the way the SSMA tables print it.

Inputs of the cold-formed steel curtain wall #

• Stud: an SSMA designation or custom dimensions; one stud or two, and where it sits in the wall. That choice sets C in S240 Table B3.2.5.1-1. Web holes are an option.
• Supports: single span, two spans, a parapet (a span and an overhang) or a knee wall (a cantilever).
• Wind: components and cladding at the strength level, from your wind calculation. It acts both ways. ASD takes 0.6 of it. The wind pressure is not derived here.
• Superimposed vertical load: S240 defines a curtain wall as carrying at most 100 lb/ft, or at most 200 lb. Over that, the calculation is not feasible: use the cold-formed stud type.
• Flange bracing: discrete bracing on both flanges; structural sheathing on one and discrete bracing on the other (S240 B1.2.2.3: at most 8 ft, studs at most 24 in.); or structural sheathing on both.
• Distortional buckling: computed by default. You may mark it restrained if that is your judgment. kφ comes from S240 Appendix 1.
• Deflection: a wind factor, 0.42 by S240 B1.1.2(c), and a limit, span / n. Your finish decides the limit. An overhang is on twice its length.
• Track and top details: track, deflection track or clip at the top; track or clip at the base. Whether both flanges are screwed, the screw, the track thickness, steel and flange, the slip gap.

Auto-design varies the section (lightest first) and the yield stress when unlocked. Wind, height, spacing and the track are kept.

Checks performed #

The limiting height is the least of flexure, shear and deflection for one or two equal spans, and on two spans bending and shear together at the interior support, with a punchout next to it if you say so. It is reported beside the checks and is not itself a check: web crippling is not in it, and the checks handle that.

Limitations #

• No axial load is combined with bending: the stud carries little, inside its definition. Use the cold-formed stud type otherwise.
• Bridging forces and their anchorage are in the cold-formed steel bridging type. Slide clips and their screws are in the connection type; their reactions are in the results.
• S240 B3.2.5.1(c), the jamb with two studs and a track of the same thickness, is not built.
• Web crippling on a two-stud position outside the equation's range uses each stud as a single web.
• The wind pressure comes from you.

Verification examples #

Verification status: 24 values compared in 23 examples (21 published, 2 hand calculations from the cited equations): 24 within tolerance, 0 recorded deviations. Code basis: the provisions it uses were read in the target edition.

• Published table values: SSMA Product Technical Guide (2022) pp. 26 to 28, 20 limiting heights and spans in single and double span tables. The table's pressures are at 0.6 W and reduced by 0.70 for deflection, which is the 42 % of S240; its 5 psf column is not reduced. Cells marked as limited by web crippling are not used. The two span values are compared with a punched web, as the guide prints them: for depths up to 4 in. the punchout reaches 0.38 of the flat web, and its moment is at the punchout.
• Hand calculations: S240 Eqs. B3.2.5.1-1 and B3.2.5.2-1 from their stated form. No published worked example of a track or deflection track is on disk; the CFSEI tech notes W100 to W103 and the AISI Framing Design Guide are paid.