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Deflection limits for skylight support framing.

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I am looking for deflection limits for designing skylight support framing.  I have a 40' x 180' gabled skylight bearing on a perimeter of W-beams spanning between steel columns at various spacings of 15' to a maximum of 40'.  The skylight MFR. has told me I must maintain a max. deflection in any direction of L/750.  That seems somewhat reasonable for horizontal deflection of a gabled skylight, but that seems way to strict for vertical deflection.  In AISC Design Guide #3, on page 21, I find a DIFFERENTIAL vertical deflection limit of L1/240 (max of 1/2") where L1 is the span of the skylight.  This would be no problem to achieve for most beam spans.  I also see L/300 for live load deflection (p. 4)... again, no problem.

I understand that AAMA has a reference: TIR A11-96.  Does anyone have this document?  Any experience with vertical deflection limit of skylight support framing would be helpful.

Bruce D. Holcomb, PE
Butler, Rosenbury & Partners
300 S. Jefferson, Suite 505
Springfield, MO 65806-2217
ph (417) 865-6100
fax (417) 865-6102

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