Designing a 3/8" thick steel gusset plate and associated fillet welds to resist angled load

[gmoney731]

Hello,

I have attached an image "Problem.png" that shows the gusset plate of interest, and the context of the loading. The axial compression load of 10 Kips is applied from the L3x3x1/4 brace to the connection at an angle of 45 degrees.

Problem.png:

https://files.engineering.com/getfi...-b3c1-4ef6-a9bb-610f69e1454b&file=Problem.PNG

I have also attached a PDF that is supplemental for my approach of the weld design.

https://files.engineering.com/getfile.aspx?folder=94d15d75-0bc1-4ff9-b199-ff0601d79bbf&file=Weld.pdf

Based on this image, I came up with several checks for both the plate and the weld:

Gusset Plate
-Check for plate bending (the X component of the angled load multiplied by the eccentricity)- AISC Chapter F
-Check for plate shear (again, the X component of the angled load) - AISC Chapter G
-Check for plate combined axial and flexure - AISC Chapter H

Weld
-Check weld per AISC 14th Design Example Chapter J.2 - fillet weld loaded at an angle, which is essentially based on Chapter J from AISC
-Check weld combined stress capacity using attached "Weld.pdf"

The members are already checked and sized using RAM Elements. Aside from maybe checking the bolted connection itself (bolt shear, bolt bearing), is there anything else I am missing?

 

[sbisteel]

Web yielding and buckling should be checked for the W8.

If there's any chance of tension in the brace, block shear & shear lag should be checked on the L3x3.

 

[dik]

Loads are pretty small, in addition, check the Whitmore section for compression of the gusset.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[DrZoidberWoop]

Are you looking for technical theoretical solution or a real world solution? Read Chapter 13 of AISC Manual or Design Guide 29 for bracing examples.

Your weld should be designed for either 1) the peak stress (which you have calculated) or 2) 1.25*average stress, but need not exceed the weld required to "develop the gusset." One thing to note, your peak stress calculations use the elastic section modulus of the weld group. It seems like the newer resources are switching over to the plastic method to analyze these weld groups (Example: AISC Seismic Design Guide 1st edition Example 2.3 uses elastic method S=(L^2)/6, and 3rd edition uses plastic method Z=(L^2)/4 for the analogous example.

For a 3/8" (assuming 50 ksi material) gusset , you are going to be defaulting to 1/4" fillet welds on each side [0.75*0.6*65*0.375/(2*1.392)]=3.94 sixteenths. This is also sometimes the practical minimum sized weld a heavy fabrication shop will apply to primary steel members.

 

[KootK]

If there's a real failure mode to be concerned with here, I'd say that it's probably the torsional rollover of the entire assembly. The plate kind of cantilevers down from the beam. Hopefully there's some transvers framing in play that makes that non-issue.

It seems like the newer resources are switching over to the plastic method to analyze these weld groups (Example: AISC Seismic Design Guide 1st edition Example 2.3 uses elastic method S=(L^2)/6, and 3rd edition uses plastic method Z=(L^2)/4 for the analogous example.

That's interesting, and surprising in my opinion. I've always been under the impression that welds themselves were not ductile enough for plastic redistribution. Do you know the justification for the change of heart?

 

[dik]

Thanks, Doc... for welds I always use the S (Z to Aussies) and for the gusset always use the Z. I never use the plastic section for welds (I think whatever plastification occurs to be a little added strength).

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik