Acceptable deflections
 

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

Acceptable deflections
 

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

Acceptable deflections
 

Proctologically Violated©® writes:

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

For tile, specs usually call for L/360 or L/720.

Acceptable deflections
 

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

Acceptable deflections
 

Some interesting stuff comes out of BeamBoy.

That .033 deflection was for a 4x13 beam (13, for the uninitiated, is the
lbs per foot of the section--the stock book from a decent steel house gives
the actual dimensions--Ryerson or Thypin, for example, good books to have).
The deflection is even smaller in a 6x9 beam, despite the much lower wt per
foot.
In 6x12, smaller still.
And a mere .009 for the same wt per foot, but in a 8x13 wide flange.

Unfortunately, I have some head room constraints, so the 4x13 beam may be
the only option. But fortunately still a viable one, deflection-wise.

It seems, from some preliminary pricing, that steelhouses charge basically
by the pound, so a 6x9 beam would in fact be substantially cheaper--and
stiffer--than a 4x13. Go figger.

Cost adds up quickly w/ this stuff. I'm looking at a few grand, just in
goddamm beams!
Might be worth bumping my head, once in a while. :)
--
Mr. P.V.'d
formerly Droll Troll
"RoyJ" wrote in message
nk.net...
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