huangyhg

handrail post weld
i have a retarded question.
if i have a standard pipe 1.5" diameter that works (s > sreqd for 35 ksi) for a 200 pound load applied at 2'10" above base, then would'nt an all around weld that has thickness equal to the thickness of the pipe work for transfering the moment?
however, when i run the numbers using the properties for treating a weld as a line (refer blodgett), i end up getting a 1/4" weld all around.
can anyone explain the load transfer and how to size these weldments?
thanks
the weld only transfers load in shear, it is not quite an extension of the post in that it doesn't transfer the load in bending. it's not quite apples to apples.
i don't know why streit says the weld only transfers the load in shear, because welds work in bending, tension, compression, whatever. if you work out the force/inch you need in bending, then select a weld size for that force, you have it. that is, as long as the weld size is not too big for the pipe wall thickness.
there are at least two differences that come to mind.
first the shear stress on a fillet weld is calculated on a plane 45 degress to the thickness, hence the term .707t
second the weld has a different allowable stress = .3fy (=.3 x 70ksi = 21 ksi for e70xx electrodes)
the above two give the value of capacity of a weld equal to
(.3fy)(.707t)l where l = length of weld & t = weld thickness
i get a 3/16" weld as working using vector method, the actual requirement is slightly more than the thickness of the pipe. same comments for reason why as steve1.
hokie-
i did not mean that the weld can't transfer a moment from the post to the support only that it does so through shear. any weld calculation is a shear on the effective throat of the weld.
just to tie my last post together with the first. the fact that it transfers the moment through shear in the weld means that simply adding a fillet with the same leg size as the pipe wall thickness doesn't automatically work. you just have to check it like you did.

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