Beam Loading Help

[ttaylorcad]

I haven't done this in years so I am hoping someone will refresh my memory. I need to find the maximum weight that can be handled safely on structural tubing (ANSI A500) class B - 2 x 2 x 16 ga wall. The weight will be uniformly distributed along a 48" span. The supports will be fixed at either end. I know this seems simple but I just want to make sure I am doing this correctly. Thanks in Advance

 

[geoffdale]

If its just strength you are looking for, do the following:
1) Determine Sx of your section.
2) Determine allowable stress (fy) of steel. Normally .66 Fy therfore you have (0.66 X 50)=33 ksi.
3) Determine allowable moment of your section.
Mmax= Fa (in psi) * sx (in in 3)/ 12
4) Mmax= w* l * l/8
where l is your span (4'-0). This will give you in pounds per foot.
Hope this helps.
Geoff

 

[JStephen]

Double check that you have the right tubing spec- I didn't realize it went down to anything that small and light. Also, check to make sure it qualifies as compact, or whatever the criteria is (IE, not too thin-walled relative to width).

 

[IFRs]

Possibly also check for crippling of the webs and shear issues at the ends. If this is a critical member, upsize it - there is essentially no money involved here. Watch for corrosion issues also. Especially if it is outdoors or the end fixity is developed by embedding in concrete.

 

[TPNY]

A500 Class B for a square tube: Fy=46ksi, not 50 ksi.

The maximum moment for the fix-fix condition (which occurs at the ends) is =wL^2/12 (not wL^2/8).

I prefer LRFD method instead of ASD, so I would take .9(Fy)Sx for the nominal moment allowed and compare it to factored max moment. Then solve for Sx. This only works if the section compact, and I think in your case, 48" is too long and the walls are too thin, therefore the section is probably non-compact.

 

[TPNY]

No solve for Sx, solve for w. Whoops, I'm thinking design, not analysis.