# Guesst Plate Design



## MOOK (Sep 11, 2009)

In AISC Seismic Design Manual

Example 2.3 Connection design

In page 2-8 and 2-9

the gusset plate length (L) used to determine bucking = 6.25 (Bottom of page 2.8) and in top of page 2.9 the gusset plate gross area (Ag) = (6.93) * (3/8)

I wonder how the number 6.93 came from? and how exactly the plate length 6.25 was determined?

Thanks for your help


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## kevo_55 (Sep 12, 2009)

Mook,

I don't have my seismic design manual with me but I believe that they are calculating the whitmore section to determine the "effective" width of the guesset plate.

Search for that, and you'll figure it out quick.

I hope this helps!


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## MOOK (Sep 12, 2009)

kevo_55 said:


> Mook,
> I don't have my seismic design manual with me but I believe that they are calculating the whitmore section to determine the "effective" width of the guesset plate.
> 
> Search for that, and you'll figure it out quick.
> ...


Thanks Kevo for your quick reply

I know it is something related to whitmore width but I cannot get the same number in the manual, however, if you get a chance to check your seismic manual please let me know, thanks


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## kevo_55 (Sep 14, 2009)

Mook,

I finally had a chance to take a look at my seismic design manual.

It seems that the manual simply pulls this number out of thin air. Honestly, I would simply use the whitmore width which was calculated to be 6.93 inches and not even think twice about it.

Just my two cents.

I hope this helps!


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## MOOK (Sep 14, 2009)

kevo_55 said:


> Mook,
> I finally had a chance to take a look at my seismic design manual.
> 
> It seems that the manual simply pulls this number out of thin air. Honestly, I would simply use the whitmore width which was calculated to be 6.93 inches and not even think twice about it.
> ...


Thanks again Kevo for your help


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## Hromis1 (Sep 16, 2009)

MOOK said:


> Thanks again Kevo for your help


Great Question Guys! That really made me go back and look up the answer in the steel design manual and I learned something new (or had forgotten in the past). FYI, Whitmore section is calculated a little differently for welded vs bolted connections. It is described on 9-3, with a diagram on 9-4 of the 13th ed.

Keep them coming!


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## Paul S (Sep 16, 2009)

I am also trying to figure out where the 6.25 in is coming from in that example, and I have yet to figure it out! I do, however, respectfully disagree that using the Whitmore length is the correct thing to do. The example is checking the compressive strength of the gusset plate, and the 6.25 in is supposed to be the average length along the centerline of the 2L6x4s perpendicular to the Whitmore length to the edge of the gusset plate. The Whitmore length is 90 perpendicular to the length that we need to check, and really doesn't make any sense to just use it.

If you fire up the fine black cd that accompanies the 13th manual, and locate example II.C-5, there is a diagram that shows the length we need to check on the gusset plate. Following that example, and taking the average length, I would say the 6.25 in is an error and the correct length to use is 8.036 in.

Does anyone else disagree with using K = 0.65 in the original example? K = 1.2 makes more sense to me.

Any thoughts or am I way off on this one?


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## kevo_55 (Sep 16, 2009)

^^ Good point Paul!

I thought the question was how this width was calculated in the first place. Now I see that the real question is "what is the "column" length to use?"

For my gusset designs I always use a K=1 and my length is typically from the center of the gusset/brace connection to the gusset edge. (along a line to the center of the beam/column.)

Maybe I should try to scale this 6.25" length from the picture shown.


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## Hromis1 (Sep 16, 2009)

On further review.....you guys are correct. It has nothing to do with the Whitmore width. It is just a fluke the two numbers are similiar. It is the "column" length for the 6.25 inches....

You could calculate that based on the geometry, CG etc....but I would hate to face that on an exam. The sentence before the 6.25 inches basically implies the whitmore width is only needed to come up with the column length...but they never explain how this is done.


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## MOOK (Sep 17, 2009)

Paul S said:


> I am also trying to figure out where the 6.25 in is coming from in that example, and I have yet to figure it out! I do, however, respectfully disagree that using the Whitmore length is the correct thing to do. The example is checking the compressive strength of the gusset plate, and the 6.25 in is supposed to be the average length along the centerline of the 2L6x4s perpendicular to the Whitmore length to the edge of the gusset plate. The Whitmore length is 90 perpendicular to the length that we need to check, and really doesn't make any sense to just use it.
> If you fire up the fine black cd that accompanies the 13th manual, and locate example II.C-5, there is a diagram that shows the length we need to check on the gusset plate. Following that example, and taking the average length, I would say the 6.25 in is an error and the correct length to use is 8.036 in.
> 
> Does anyone else disagree with using K = 0.65 in the original example? K = 1.2 makes more sense to me.
> ...



Paul

Example II.C-5 in Which Chapter??


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## Paul S (Sep 17, 2009)

MOOK said:


> PaulExample II.C-5 in Which Chapter??


That example is on the black cd that came with the AISC Manual, it is not in the Manual. I have the entire thing printed out and spiral bound for quick reference.


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## MOOK (Sep 17, 2009)

Paul S said:


> That example is on the black cd that came with the AISC Manual, it is not in the Manual. I have the entire thing printed out and spiral bound for quick reference.


I got it, thanks Paul

However, I still have 2 questions regarding the same problem.

1- Why the buckling factor "K" was not multiplied by the Leaning Column Amplifier to determine Pe2 in page

2-26?

2- Why we assumed Plt = zero (Page 2-24)?


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## bcy (Sep 30, 2009)

Paul S said:


> If you fire up the fine black cd that accompanies the 13th manual, and locate example II.C-5, there is a diagram that shows the length we need to check on the gusset plate. Following that example, and taking the average length, I would say the 6.25 in is an error and the correct length to use is 8.036 in.
> Does anyone else disagree with using K = 0.65 in the original example? K = 1.2 makes more sense to me.
> 
> Any thoughts or am I way off on this one?


The average length from the attached sketch agrees with your number, (11.280+8.146+4.686)/3=8.037".

I tend to use k=0.65 as the gusset plate is connected to both beam and column flanges. The extension of the Whitmore section baseline shows that majority of the buckling length is restrained from the beam/column flanges. Sidesway is unlikely to occur. any thoughts?

gusset_length.pdf


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