Braced Frame

[ars13]

I have a 2 story braced frame. The diagonal braces are broken at the 1st story and designed using those lenghts respectively. The beam at the first story is not braced by the floor diaphragm. Am I right to say that the beam at the 1st story has to be designed as a lateral brace or provide stability for the diagonal members? If so, how much should it be designed for? Does the AISC have a design guide for lateral bracing?

 

[vandede427]

If you designed the brace for the total distance, I believe you'd have to transfer the out-of-plane bending moment of the brace through it's connections to the beam. I may be wrong on that.

I would design the beam to have enough out-of-plane stiffness to "brace the braces" (for lack of a better term) for 2" of the max brace compression force should be adequate.

If it's only 10' long and not tied into a floor diaphragm, you could just rotate the beam 90 degrees on it's longitudianl axis and provide a small more column like section like a W8x31 or something.

 

[DaveAtkins]

What you are doing is unusual--can't you orient the diagonals in a more typical fashion, where the ends of the diagonals occur at the intersections of beams and columns?

DaveAtkins

 

[PEinVA]

Only guess on the layout is some architect wants doors (left side on the 2nd floor, and right side 1st floor)

We as SE have to learn to just say no sometimes I think.

However, that being said, if that beam isn't in the diaphragm, why do you need it there?

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[csd72]

ther has been a recent post on a similar issue with bracing. Use the ggogle search at the top of the page.

 

[ars13]

Thanks for the responses. Yes, the reasoning for the configuration is because of an exterior door. The 1st floor beam is a horizontal wind girt.

After taking another look, we were able to relocate the door slightly. Now I can fully brace the upper frame and bring the brace of the lower frame into the beam/column node at the first floor.

Thanks for the help.