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Weld Stress

Weld Stress

Weld Stress

Hello all, I am trying to analyze the stress in an attachment weld in order to determine the minimum allowable fillet weld leg length (w) by using the following formula:

w = f/fw

where f = actual force [lbs]
      fw = maximum allowable unit force on an equal-leg
           fillet weld equal to 1"  [lbs/linear inch]
          = .707*E*Sa
      E = joint efficiency based on throat area
      Sa = maximum allowable stress of the base metal

I am trying to find the correct value for the allowable stress of a weld (Sa).  I am using E70XX electrodes and welding A36 structural steel I beams and angles to a SA-516-70 presure vessel shell.  

My questions are as follows:

1) is the value of Sa = 21,000 psi
2) is it correct to assume an E of 1.0?

I have also seen the formula for fw written as follows:

fw = .707*w T

where fw = allowable force on the fillet weld, 1" long
      w = leg size of fillet weld
      T = allowable shear stress on throat of weld

any comments?

RE: Weld Stress

I have not seen the term "joint efficiency, E" before.  Your two formulae look very similar, otherwise, to me.

If you are designing per AISC ASD, then the allowable stress for E70 electrodes is 0.3 x 70 = 21 ksi.

If you are designing per AISC LRFD, then the maximum stress for E70 electrodes is 0.6 x 0.75 x 70 = 31.5 ksi.

We normally use your second formula.

RE: Weld Stress

Note also that some codes limit the actual allowable to the tensile stress of the base metal.

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