Most building codes for RESIDENTIAL use specify 1/180 deflection for
roof loads (asphalt shinges) either 1/240 or 1/360 for LIVE load ONLY on
floor joists, 1/720 deflection for special cases like tile floors. Some
codes alow derating for snow loads and the like.

A 1/240 deflection will feel like a cheap building when you walk on it,
pretty bouncy. 1/180 will feel slightly unsafe.

All of these are at the center of the joist span which includes the sum
of deflection on the support beams plus the floor joists.

Steel beam aplications tend to be limited by the strength of the beam,
wood beam applications tens to wimp out on deflection first. You have to
calcualte both.

..033" on 6' span says you are using a steel beam, getting 1/2200
deflection. That is a VERY stiff beam.



Christopher Tidy wrote:

Proctologically Violated©® wrote:

Awl--

When choosing beams for supporting roofs, floors, etc, what is an
acceptable deflection over a given length?

I'm looking at a 12 ft beam, supported at 0, 6, 12 ft, and depending
on the beam I choose (and various point/distributed loads), I'm
winding up w/ deflections of between .010 and .033 between supports,
ie, at about 3 and 9 ft.

What is acceptable? Is this a matter of local codes, or do
rules-of-thumb apply here?
--
Mr. P.V.'d
formerly Droll Troll


0.010 and 0.033 inches? My gut reaction is that this is fine. Some
overhead rolling cranes deflect by this much. But someone will probably
shoot me for saying this without knowing every detail of your design :-).

Chris