Simple weld group engineering question

[theonlynamenottaken]

If I'm calculating stresses in a weld group due to out of plane bending, as in a rectangular tube fillet welded all-around to a rigidly supported base plate:

Section modulus = bd + d*d/3 based on a line thickness of unity (1.0). Then say for instance, that b=2 and d=3 so that the equation yields 9.0 (using line thickness = 1.0). Do you just multiply by weld throat size to "scale" the value down correctly? I.E., if the weld throat was .333 would the correct section modulus be 3.0?

 

[aggman]

Your formula will yield #/inch or kips/in. By applying the general flexural formula you get the following:

fw = M/S

fw = force in weld (kip/in)
M = applied bending moment (kip-in)
S = Section Modulus (in*in)

Then for say a fillet weld...

Fw = Allowable weld Stress * effective throat

effective throat = .707 * tw (for a 45 degree fillet)
tw = weld thickness = 1/4" or 5/16" etc.

setting (Fw = fw) you can solve for tw. I am not sure if that's what your looking for, but that is the general procedure.

 

[theonlynamenottaken]

Ok. What aggman said and what I said result in the same values. If you multiply the section modulus (based on thickness = 1.0) by the throat you end up with units^3. Then you can combine stresses such as P/A, Ty/Ip, V/A. Otherwise I'd have to write A = area as a function of lines with thickness = 1.0, solve everything for tw...