Steel Braced Frame - Brace Locations
Steel Braced Frame - Brace Locations
(OP)
Considering the following:
-square
-single storey
-conventionally framed structural steel braced frame
-OWSJ's & metal deck w/ diaphram action
-HSS columns and wide flange beams
-diagnol bracing on each of the four exterior walls
What is everyone's opinion on the ideal braced bay locations and the type of bracing if they can go anywhere and be anything?
Also, does anyone have any literature on best practices for such building stability design.
Thanks!
-square
-single storey
-conventionally framed structural steel braced frame
-OWSJ's & metal deck w/ diaphram action
-HSS columns and wide flange beams
-diagnol bracing on each of the four exterior walls
What is everyone's opinion on the ideal braced bay locations and the type of bracing if they can go anywhere and be anything?
Also, does anyone have any literature on best practices for such building stability design.
Thanks!






RE: Steel Braced Frame - Brace Locations
RE: Steel Braced Frame - Brace Locations
I think an X-brace will be the cheapest, because the members will be tension only (and can be rods or small angles).
DaveAtkins
RE: Steel Braced Frame - Brace Locations
1) You don't have to deal with any significant self weight sag in the braces (rod/angle problem).
2) You can detail the two braces to bypass one another without inducing much eccentricity in the brace-column connection (rod problem).
3) There's hardly any shear lag to deal with (angle problem).
A channel brace usually requires a bit more steel but I've yet to hear anyone complain. In my experience, a double C8 channel will work in the vast majority of low rise bracing situations. It makes for easy preliminary design!
RE: Steel Braced Frame - Brace Locations
Of course, this a very vague conversation to begin with....so....
RE: Steel Braced Frame - Brace Locations
They are large. No argument there. However, they're still relatively insignificant compared to the overall cost of the structure.
Where the loads justify it -- which is quite often -- I go with single C8's. Or C6's if I can get the job done with two or three bolts.
I think the geometry is slick. I center the connection plates on each column, place the two braces on either side of the plates, and connect the braces where they cross using a spacer plate of the same thickness.
It's not rocket science but it sure does make for nice clean brace. I mostly just hate to see sag in my braces when I visit the site. It offends my structural sensibilities.
I also worry that it introduces non-linearity and extra drift into my braced frames that I didn't bother to model. I've used some steel rod bracing in tall glulam frames in the past. Because the frames are wooden, you can't pretension the heck out of the brace from the get-go like you can with a steel structure. When I look at the sag in some of the these braces, I get the sense that the frames would have to deflect a foot before the braces would be fully engaged.
RE: Steel Braced Frame - Brace Locations
I typically use double angles with gussets as you describe and detail them such that they are short according to an old detailing reference I have. The guys in the field usually have to drift-pin them in, but I never have any sag that is readily visable.
Since double angles can get wide and take up wall space, I also use square HSS with knife plates. Very clean looking. On large braces I have used large HSS, pipes, and WF's. You're double channels might be something I could use in the future in place of WF's to simplify details.
RE: Steel Braced Frame - Brace Locations
I use a lot of HSS too. I use them exclusively when the brace is actually within a wall system. You can get some out of plane capacity out of an HSS brace which is good.
Do you use WT's at the ends of the HSS braces or a plate slotted into the walls of the HSS?
RE: Steel Braced Frame - Brace Locations
The HSS I use for braces are usually on WF columns.
I have used through plates to connect to HSS before, however.
RE: Steel Braced Frame - Brace Locations
DaveAtkins
RE: Steel Braced Frame - Brace Locations
RE: Steel Braced Frame - Brace Locations
RE: Steel Braced Frame - Brace Locations
If you only have a few bays then the effects will not be as great. If only two bays, well, then it is obvious which bay to brace:)
If you really have this much flexibility, it sounds like a damn good job to have!!! The kind we all dream about.