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RE: ROOF DECK EQUIVALENT THICKNESS

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JJ,

This is the approach that I took once to include a flexible metal deck
in a FEM model.  I took the example on pg. 68 of Vulcraft's roof deck
manual and created a model with shell elements that had the same loads
and dimensions as the example.  The thicknesses of the steel shell
elements were then varied until the deflection in the model equaled the
deflection in the example.  This gives the equivalent thickness for the
roof deck with a particular fastening pattern.

As Christopher mentioned, the in-plane and out-of-plane stiffnesses of
the equivalent shell will not have the correct relationship as for the
actual metal deck.  The bending stiffness of the shell will also not be
correct for parallel vs. perpendicular deck spans.  The shells will only
be good for in-plane loadings.  All gravity loads will have to be
directly applied to the supporting members.  Also, the shell elements
will affect the bending stiffness of the supporting members.  I would
save the model to another file and run it with the shells deleted to
verify the supporting members without any effects from the shells.

This approach is basically only good for distributing loads and
calculating lateral roof deflections between lines of vertical
resistance.  The shells are time consuming to put into the model and can
be time consuming in terms of the model run time.  The load distribution
and deflections are easy to calculate by hand in most cases.  From my
experience, including the deck in the model was more trouble than it was
worth.

David Dickey
Lexington, KY


-----Original Message-----
From: John J. Treff [mailto:jjtreff(--nospam--at)hotmail.com]
Sent: Sunday, August 14, 2005 7:13 PM
To: seaint(--nospam--at)seaint.org
Subject: ROOF DECK EQUIVALENT THICKNESS


Hello,
Are there any formulae, tables or procedures to calculate the equivalent

thickness of a roof deck as a flat plate?  I'd like to use shells in a 
software program as roof sheeting and need to come up with an equivalent

thickness for the shells since I can not input the steel sheet shape. I 
assume the material I will specify for the deck will be the same as the
one 
the steel deck.

Thank you,

JJ



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