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Re: Theatre Roof

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Paul Ransom,
Gary Hodgson,

        Thank you for replying to my posting on the Theatre Roof.  I
appreciate it.

Best regards,

H. Daryl Richardson

Paul Ransom wrote:

> > From: Daryl Richardson <h.d.richardson(--nospam--at)shaw.ca>
>
> >         I'm designing a theatre which will have exposed steel trusses in
> > the order of 20' centres radiating from the general area of the stage.
> > The span at the centreline ridge is 82'; there are four additional
>
> > 1.)  Can I design the truss verticals and the purlins as a rigid frame
> > "T" to provide support for the bottom chord via this frame action?
>
> Yes.
>
> > 2.)  Can I frame a "knee brace" from the mid height of the truss
> > vertical to purlins on one or both sides?  I have done this before for
>
> Yes. This is a minor variation on x-bracing between joists. Watch
> bending stiffness in the vertical.
>
> > Neither the AISC or the CISC codes address this problem directly (at
>
> Stability bracing. Lateral-torsional. See Yura/Hellwig and the SSRC
> Guide to Stability Design Criteria for Metal Structures. Note that their
> recommendations are conservative. It depends on how much time you want
> to spend to optimize the design.
>
> >         I have designed triangular trusses with two separate top chords
> > and one bottom chord before and I could do it again, however, the
> > changes in slope complicate the construction and it may not look too
> > good.
>
> Sounds like an inverted bridge truss. Pony Truss? The knee-brace
> approach will probably be more material/cost efficient but the T may be
> more appealing to the architect. The bottom chord rotational restraint
> will be a function of purlin bending stiffness.
>
> Don't forget to resolve the truss lateral forces between stabilizers
> (e.g. roof diaphragm or other bracing).
>
> --
> Paul Ransom, P. Eng.
> Civil/Structural/Project/International
> Burlington, Ontario, Canada
> <mailto:ad026(--nospam--at)hwcn.org> <http://www.hwcn.org/~ad026/civil.html>
>
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