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Re: Steel Deck Diaphragm

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Per UBC 1997 1630.6, "diaphrams shall be considered flexible for the
purposes of distribution of 
story shear and torsional moment when the maximum lateral deformation of
the diaphram is more
 than two (2) times the average story drift of the associated story."

However the SDI (Steel Deck Institute) design manual has a chart for
flexible, semi-flexible, 
semi-rigid, and rigid. It also has an example showing how to determine
the stiffness value. 
It is based on spacing of support members, number and spacing of puddle
welds, etc. 

Hope this helps.

Desi J. Kiss, MS, PE
Mission Viejo, CA 92692

On Fri, 10 Jan 2003 13:14:14 -0500 "Daniel Souter, E.I."
<dsouter(--nospam--at)> writes:
> My question relates to the use of steel deck as a roof diaphragm on a
> building with Masonry Shear Walls.  My understanding was that 
> normally steel
> roof deck with no concrete fill would be considered a ?flexible 
> diaphragm?.
> The Masonry Designer Guide by TMS contains a table (8.4.1) ?Maximum 
> Span to
> Width Ratios for Horizontal Diaphragms to be Considered Rigid?.  
> According
> to this, ?Metal Deck with No Fill? may be considered rigid if it has 
> a span
> to width ratio of 2:1 or less.
> The IBC states that a diaphragm is rigid unless; ?Lateral 
> deformation of the
> diaphragm is more than two times the average story drift of the 
> associated
> story determined by comparing the computed maximum in-plane 
> deflection of
> the diaphragm itself under lateral load.?
> Do these provisions mean that metal roof deck can transfer torsional 
> shear
> provided the proposed building meets the above criteria and of 
> course that
> the values for diaphragm strength and stiffness and diaphragm chord
> strengths are acceptable?
> I would appreciate if somebody could recommend any reference or 
> resource
> dealing with steel deck diaphragms, in addition to the ?SDI 
> Diaphragm Design
> Manual? which I already have.  Specifically anything that might deal 
> with a
> diaphragm cantilevering in plan out from the shear wall and the 
> limitations
> on this type of potential building plan.
> Thank you.
> Daniel Souter
> Florida

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