Lateral bracing to existing steel beam
Lateral bracing to existing steel beam
(OP)
I am designing lateral bracing to several existing steel beams that were installed many years ago, at the underside of a waffle slab. Attached are 2 options, but both require a fair amount of field welding which is expensive and time consuming. The first option probably does not work because the minimum required concrete thickness for the KWIK bolt is 3" and the waffle slab is only 2½" thick (although perhaps the topping could be considered as adding to the slab thickness, but probably not prudent to do so).
Does anyone have any ideas for a better brace, with less field welding? Note that the position of the steel beam varies relative to the rib of the waffle, but it never is directly under the rib.
Does anyone have any ideas for a better brace, with less field welding? Note that the position of the steel beam varies relative to the rib of the waffle, but it never is directly under the rib.






RE: Lateral bracing to existing steel beam
And I wouldn't worry about the welding. A lot of times field welding is preferred by contractors to field bolting, because there is more tolerance in the field.
DaveAtkins
RE: Lateral bracing to existing steel beam
I have an idea though...use a "U" shaped plate say 4" long and 4" wider than the concrete rib, to fit under the rib and extend say 4" up each side of the rib. The bottom of the U shaped plate would be shop welded to a small L strut extending to the flange of the steel beam that is to be laterally braced. The spaced between the U shaped steel plate and the concrete rib would be filled with grout. I will try drawing it up and see how it looks.
Thanks for the comments.
RE: Lateral bracing to existing steel beam
I cant tell what is directly above the steel beam, but below the underside of conc rib. if there is space there, you could use a single angle on top, exting out in both directions, and then add some type of stub up between each rib, using compression only, would avoud you having to drill anything into the concrete.
RE: Lateral bracing to existing steel beam
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Lateral bracing to existing steel beam
BA
RE: Lateral bracing to existing steel beam
I am a bit reluctant to field drill a hole thru the beam flange. Can they do that neatly without weakening the flange? I like the BARetired idea, but I am not sure if it may be grouted above the beam, all the way up the waffle void to the underside of the 2½" slab. It is currently all covered with spray fireproofing so I can't see until removing the fireproofing, but I suppose could break any grout out locally. Is a bit confined to reach in to weld on top of the beam, but we can ask the welder if he can do it.
Thanks for the time and thought you all put into this. It is very much appreciated.
RE: Lateral bracing to existing steel beam
RE: Lateral bracing to existing steel beam
They can. As long as flange net rupture strength exceeds gross yield strength, you're good. We do it all the time for wood nailer attachment.
One attractive feature of BA's scheme is that all of the assemblies would be identical.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Lateral bracing to existing steel beam
The ability to drill the flange acceptably is just dependent on the equipment. The dimensions of the drill, i.e. length including bit, and clearance from web, need to be checked. Overhead drills like this are heavy, and magnetic is best. You probably don't need a 3/4" bolt.
RE: Lateral bracing to existing steel beam
That's exactly what it's for. I considered one side -- and even bottom -- but the asymmetry gnawed at me. In the interest of avoiding the cut:
1) Channels if they'd work.
2) Two 4x4 angles, diamond like. Same torsional value.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Lateral bracing to existing steel beam
RE: Lateral bracing to existing steel beam
You would have to have two 8x8 angles to achieve the same torsional profile.
The asymmetry would not bother me for torsional resistance, but I like BA's simple top flange brace better.
RE: Lateral bracing to existing steel beam
Heck, could probably be unistrut and some screws for all the difference it would make.
U-shoe thing would be extra slick if the bottom of the shoe were level with the underside of flange. You could use a horizontal angle brace and conceivably bolt all of that together.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Lateral bracing to existing steel beam
For how much of the length of the beam would the torsional strengthening be required? How can that be determined?
Yes I can I believe make the bottom of the "U" flush with the beam flange.
Thanks everyone for the ideas and time that you have put into this. It is very much appreciated. Now I have to think and decide.
Another matter - has anyone ever had a problem with this site, that after typing in a whole lot, it suddenly disappears, possibly due to inadvertently touching the wrong key I suppose? Is there any way of getting it back when that happens?
RE: Lateral bracing to existing steel beam
It can be. You just improve the torsional parameters that go into your LTB bracing calc until you don't need bracing.
It could surely be cut short a bit but I doubt it would be worth the hassle of trying to sort out the theory.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Lateral bracing to existing steel beam
RE: Lateral bracing to existing steel beam
if field drill is needed, it would be an electromagnetic drill likely, depending on flange size, may be a little tough to fit, bot not impossible
RE: Lateral bracing to existing steel beam
what often happens to me on all forums, bulletin boards and documents is I highlight a word or short section with the mouse, then start to type what I want to overwrite the highlighted section. Apparently the un-tended mouse shifts a little bit, and highlights a huge alternate section when I'm not looking, so my new typing replaces it.
<CTR> Z often takes me back
RE: Lateral bracing to existing steel beam
To TMoose - very interesting. I will give CTR Z a try next time it happens.
RE: Lateral bracing to existing steel beam
RE: Lateral bracing to existing steel beam
One of the thinks that I enjoy about ajk1's threads is that the crux of them usually revolves around coming up with a creative, build-able detail for a tricky renovation situation. They're like clean little homework problems where you don't need to bother with any math. Plus you get to do some drawing and compare your answers with the other kids.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Lateral bracing to existing steel beam
heh well it'll be hard to top bolting on two 1/2 HSS sections to prevent LTB
RE: Lateral bracing to existing steel beam
Right? And you'll notice that, despite that solution being whacky and an unlikely final choice, ajk's still willing to give it some legitimate consideration. Safe space -- I love it. And, one time in ten, that whacky solution winds up being the dark horse best solution.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Lateral bracing to existing steel beam