AISC 360-10, Chapter J10.8 Clarifications 1

[question_asker]

Looking for a couple of clarifications in Chapter J10.8 for transverse stiffeners.

1.)

Regarding the 25*tw vs. 12*tw length of web considered to be part of the "built-up" column. If I have a pair of bearing stiffeners *near* the end of my member, but the 25*tw dimension is still within the dimensions of the end of my beam when centered about the stiffeners/bearing CL, can I use the full 25*tw vs. the 12*tw specified for stiffeners at the end of members? My CL bearing will be 9" +/- from the end of beam, and I am using a W36x160 (web = 0.65", 25 * 0.65" = 16.25").

2.)

Additional requirement (2) at the end of J10.8 reads:

"The thickness of a stiffener shall not be less than one-half the thickness of the flange or moment connection plate delivering the concentrated load, nor less than the width divided by 16."

Is the "width divided by 16" referring to the stiffener width divided by 16, or the aforementioned flange width divided by 16? My assumption has been that it is the former, i.e. for a 4" wide stiffener, minimum thickness = 4/16 = 1/4". However, I wanted to get your opinion.

I searched through previous threads for these clarifications but could not find anything. I also looked through the commentary but did not see any guidance on these particular items.

Thank you.

 

[question_asker]

Any thoughts?

 

[JoshPlumSE]

Is the "width divided by 16" referring to the stiffener width divided by 16, or the aforementioned flange width divided by 16? My assumption has been that it is the former, i.e. for a 4" wide stiffener, minimum thickness = 4/16 = 1/4". However, I wanted to get your opinion.

I'm not sure. I've gone back and forth on it. My tendency is to say that it's either. You shouldn't have a stiffener that is stiffening a column flange if the element that's applying the load is wider than 16 times the thickness of the stiffener. Nor should the stiffer thickness be less than 16 times the width of the stiffener.

The commentary does point to some other references for more information on designing stiffeners. You might want to check out those references to see if there is any more clarity there.

 

[KootK]

Your instincts are robust on both counts.

1) Yes. It's an effective width thing. No. Matter where the stiffener is located, you get whatever physically exists with 12x either side of the stiffener.

2) It is in relation to the width of the stiffener being designed. It's basically a b/t slendetnesd ratio to keep the stiffener from buckling.

 

[question_asker]

Thank you both for your input and clarifications.