Working Point for Braced Frames

[Charlie Delta Whiskey]

Attached is a drawing of a braced frame I am working on. It is my first one that I have done and the firm I work at hasn't done any braced frames before. We mainly do residential stuff and this is a small warehouse we are currently working on. My question is about the line of the brace, working point, or W.P. At the base I have the w.p. at the middle of the baseplate. In the middle of the X I have the w.p. centered on the beam. At the upper corners I have the w.p.at the column face at the middle depth of the beam. Is this the correct way to do it? Is there a correct way to do it? I have looked in the AISC seismic provisions and scoured eng-tips to no avail. Any guidance would be greatly appreciated.

 

[canwesteng]

I'd put workpoints at the column center line. That's probably how you've modeled it anyway.

 

[atrizzy]

Center of column and mid-depth of the beam is best practice in my opinion. You can make other arrangements work, but there will be small (though possibly not insignificant) eccentricities you may need to address.

 

[WARose]

I usually dimension off of the TOS (Top Of Steel) or TOC (Top Of Concrete) given in terms of elevation. If I have to provide a WP (Work Point)......it would be the intersection of the center line of the column and the beam.

2 things that are jumping out at me in this is: you are not giving a elevation here and you are dimensioning to a bottom bolt on a brace. For the latter, I would think that would be pointless as the shop will likely try to do something different (in their drawings). For the former, even if you don't have one (via a survey) you need to set one somehow.

 

[T_Bat]

This may be implied by the answers above, but typically the work point at the base plate is at the bottom of the plate and the center of the column. Top of base plate works to but unless you need away from the column I would keep it at the column centerline at the base.

 

[T_Bat]

I'll also add that there is a discussion on this in AISC Design Guide 29: Vertical Bracing. It's free for AISC members if you or someone in your firm is a member. It basically echoes what's been shared above.

 

[Charlie Delta Whiskey]

Thanks everyone for the tips. It makes sense now that I would put the working point at the centerline of columns and beams in order to most closely follow my frame model and to avoid any eccentricities or moments on the baseplate or elsewhere. As for dimensioning to the erection bolt on the brace, that dimension is actually just showing where the top of the thickened slab will be, 1'-0" above the top of the pier. It just happens to go right across that bolt.

Thanks for the tip on that AISC DG.