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Matthew Shear wrote:

I am designing a one-story building of light frame construction using SCBF; I was wondering when a zipper column is required? I have been unable to find a source on when it is required.

Thank you,


A zipper column is used to change the brace configuration from an inverted V (2 braces meeting at the middle of the roof beam) to a pair of diagonal braces. There used to be an exemption in the AISC Seismic Provisions that allowed you to ignore the effects of the maximum unbalanced seismic forces (2005 AISC 13.4a (3)) for one story buildings and the upper story of multistory buildings. This exemption has been eliminated in the latest edition (AISC 341-05 13.4a). As a consequence, for inverted V brace configurations, the W beam can get very big, see the new AISC Seismic Design Manual, page 3-46. The zipper column may result in savings by reducing the W beam size, although there is the additional weight of the new column and costs from more fabrication.

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