Re: steel tubing strenght formulas ??

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<davemucha@j...> wrote:

> yikes ! A 3 inch squate tube with 1/8 wall and only a 50 pound
> load will deflect about 4 thou.
>
> A 100 pound load will deflect about 8 thou.
>
> Neither is too bad for a plasma cutter, but both are horrible for a
> router.
>
> Dave

Dave, the end conditions are a big factor in deflection. if you have
a leg at each end of the tube and nothing else but the single tube
tying the legs together then the ends of the tube would be essentially
free and you'd get max deflection for a given load. If there's a
second member tying the two legs together, then the end condition of
the tube more approaches fixed end conditions which result in less
deflection. Vertical bridging between the two horizontal members
creates a truss which can drastically reduce the deflection since its
roughly related to the cube of the height. The AISC Manual for Steel
Construction covers situations like this, but structural analysis in
general is not a quick and simple thing once there are redundant load
paths, etc.