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Re: W8 Reinforcement

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> From: "Michael Zaitz" <mzaitz(--nospam--at)hgbd.com>

> steel joists, however when we questioned if we could hang from the
> joists we were told no (the joists were to be designed for a 15 psf
> collateral load).  Regarding allowable deflection I am aiming for L/240

Why not run a couple unistruts between a pair of joists, share the load
and get double the capacity and stiffness (e.g. 2*L/180 or whatever -
see below)?

Maybe you didn't ask the right question ... A metal building engineer
will assess the pipe load as an additional load above the 15 psf,
otherwise, you wouldn't be asking. Or, the proposed support locations
and point loads may exceed the effect of a 15 psf UDL, which was
specified.

A sch40 10" water-filled pipe is about 75plf which would exactly match a
15 psf collateral UDL on joists typically spaced 5' c/c, running
parallel.

You have an additional requirement for L/240 which probably exceeds the
joist stiffness (let alone the frame stiffness). A stiffness is rarely
included in a metal building order (pity). I would expect an upper limit
joist stiffness closer to L/180 would be common, when unspecified.
Additionally, the joists are not static and will fluctuate with the roof
loads (wind, snow) which may not be good for a 10" pipe.

With a static member (e.g. independent W8) when you are compensating for
the member deflection with hangers, why do you care about L/240? Aside
from empty and full ... Also, judicious location of supports may
mitigate stiffness and deflection issues.

-- 
Paul Ransom, P. Eng.
Civil/Structural/Project/International
Burlington, Ontario, Canada
<mailto:ad026(--nospam--at)hwcn.org> <http://www.hwcn.org/~ad026/civil.html>