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# Gusset Plate Stiffener Design

## Gusset Plate Stiffener Design

(OP)
Hi, I have a question regarding the calculation for the required thickness of the gusset plate when is used for stiffening the bending of the steel angle. (See attached drawing) Without the gusset plate, the moment resistant of the steel angle is insufficient to resist the moment created by the eccentrically applied load at the tip of the angle flange, therefore we sometimes introduce the gusset steel plate in perpendicular direction between the two legs of the steel angle. I use the section modulus of the gusset plate (thickness and depth of gusset plate) to determine the min. thickness of gusset plate required, but I'm not confidence if I'm doing right.

Can anyone provide me feedback on how to check the required thickness of the gusset plate?

Thank you

### RE: Gusset Plate Stiffener Design

I usually treat it likely a compression member and make sure its thickness has a high enough r to meet the slenderness requirements for a member in compression.

### RE: Gusset Plate Stiffener Design

By inspection I would say 1/4" is sufficient for 10 kN on the attaced drawing. My approach is usually to check elastic stresses in the stiffener, combining bending and shear to get your principal stresses, and comparing to the yield of the material. Jayrods approach seems good as well. A thicker stiffener doesn't add any real cost to the detail, so whatever lower bound solution you can be satisfied with would be good.

### RE: Gusset Plate Stiffener Design

I would think a 5/8" thick angle could take a ~2.25 kip (10 kN) reaction with no trouble. Can't you reduce your considered eccentricity by considering the centroid of an assumed bearing stress (uniform?) on the angle leg and taking the eccentricity to the edge of the fillet of the angle? Also, if you are designing using LRFD methodology, why not consider the plastic moment capacity of the angle leg?

### RE: Gusset Plate Stiffener Design

(OP)
Hi Jayrod12, Could you show me the calculation how you would calculate the r for this triangle shape gusset plate? If this was rectangular shape, the slenderness could've been calculated with the width and thickness of the cross section of gusset plate, but I don't know how I'd approach with this triangular shape gusset plate. Thank you

### RE: Gusset Plate Stiffener Design

(OP)
Hi canwesteng, would you mind show me how you would combining the bending and shear to get the principal stresses for this case? I'd appreciate for that. Thank you

### RE: Gusset Plate Stiffener Design

r of a rectangle is d/3^0.5. d would be the plate thickness.

### RE: Gusset Plate Stiffener Design

Principal stress isn't the right word, I'm using von Mises yield criterion. See the paper by Larry Muir on extended shear tab design here https://pdfs.semanticscholar.org/191a/90afccb1c1b2... (used to be on larrymuir.com but the site is down), under sizing the plate for strength and ductility. Take moment over section modulus, and shear over area, to find your flexural and shear stresses.

### RE: Gusset Plate Stiffener Design

Rotate this thing 90 degrees and you've got a classic beam to column seat connection. And canned, experimentally verified solutions for bolts, welds, stiffeners, and no stiffeners in the AISC manual. They also have a method for evaluating the stiffeners of such connections I believe. I'd think that the most appropriate tool for evaluation your situation.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

### RE: Gusset Plate Stiffener Design

Jsu0512:
One of the things I’d watch out for on the detail you show, is the way the angle is welded to the WF. In either detail, your load on the angle leg tip induces a significant prying/tension/uplift load on the weld terminations right near the heel of the angle. These weld terminations are problematic under any load condition, they are the weak spot in the weld. Then you are applying a concentrated prying load on them. They can unzip pretty easily under those combined stress conditions and be a crack starting point. You might do well to run a 3" long weld across the beam flange and to the 4" angle heel.

### RE: Gusset Plate Stiffener Design

The cost of cutting the stiffener plate on an angle is likely more expensive than leaving it rectangular, just use a grinder to knock off the sharp corner (unless you have a kazillion of them and an automated cutting bed). How is the load applied at the very top of the angle? Without a stiffener, as the angle deflects, the point of load application reduces the eccentricity.

Dik

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