Question regarding weld subjected to combined shear and moment (EIT)

[onlym112]

Hello,

I have a question about AISC 15th edition manual equation 8-14 for calculating shear per linear inch of weld due to an applied moment. It is my understanding/intuition that welds are brittle, so when calculating fb, I would divide the applied moment by the elastic section modulus rather than the plastic section modulus. I believe that a weld would not behave so plastically, so using the elastic section would be prudent. Can anyone explain why AISC uses the plastic section instead of the elastic? or could you point me to a source that can help me understand this topic better?

Thank you

 

[271828]

You're looking in the section called "Plastic Method." The text says the strength could be computed using the instantaneous center of rotation method and the equations you're looking at are a simplification.

The ICoR method relies on the weld having some ability to deform inelastically as described near Equation 8-3 and Figure 8-5. It is a well established method.

 

[onlym112]

Makes sense. Thank you!