Looking for an elusive stress formula

[DesignerMike]

I have been digging through my old text books looking for a formula (that I used about a year ago and misplaced).

I need a simple formula to find stress of a flat square plate, fixed on edges, with a pipe welded to the center. There is a relatively large moment force on the pipe, and I know the plate is very weak (can't do a gusset either)

Thanks for the help.

 

[prex]

If you mean that the plate has a center concentrated couple, Roark has formulae for a circular plate with built in edges. You can use a circular plate with the same area, or, if you want to stay on the safe side, with a diameter equal to the side of your plate.

prex

http://www.xcalcs.com

Online tools for structural design

 

[borjame]

Is there a moment like you're pushing on the opposite end of the pipe so it will "tear" out or is there a couple so that the pipe is twisting out. Two separate problems.

Both are shear problems where either the weld will give or the plate. It sounds like the plate will give first since any weld bead will locally thicken up the plate (given a good weld).

If you're twisting the pipe, shear due to torque is

shear = T*c/J
T - torque
c - radial distance area of concern
J - polar mom of inertia (pi*r^4/4)

If you're prying the pipe out it's much more complicated as the plate will bend taking some load and how the plate is supported beyond it's edges comes into play (i.e. is the plate on the ground so one edge of the plate can't deform down as you pry, etc). 6 24 21b A good start would be Roarks (6th edition, table 24, case 21b) like PREX said, I would post but there's a table so it gets messy to type.

Hope this helps.

 

[DesignerMike]

Sorry about a lack of info.

Actually, very little torque on the pipe.

Basically, weld a pipe to center of a flat plate (perpendicular, like a lampbase). Then take the pipe with plate and weld around the plate to a vertical column. Hang some weight at end of the pipe (kindoff like a sign sticking out from the face of a building). No other support, just cantilevered pipe welded to a plate.

Pipe is like 22" diam with 3/4" wall to a 1/4" thick 51" x 51" plate. (knowing the plate is far to thin at this point, and pipe is much larger than required for the loading, but it is that size for other reasons).

I wish I could post an image or drawing to explain myself better.