More Art of Diagonal Bracing
More Art of Diagonal Bracing
(OP)
Hi again guys,
Another question related to the configuration of lateral braces and brace connections...
My steel detailing books do not address the connection of diagonals to column webs. I have only found one online example that uses the method I illustrate here...that is using a wide flange tension/compression brace that is the same depth as the column and has a gamma of 90 degrees so that the flanges of brace and column connect directly. I realize that if the lateral loads are light that this type of brace may be oversized and there are also practical clearance considerations for W8 columns.
I'd just like to hear the thought process you guys go through when choosing members sizes/types/configuration for these types of connections. In my case the bracing loads may be light since only the top 14' of the 64' tower is exposed. In that case I would have no problem using a WT or double angle (possibly x-brace) connected directly to a gusset that is welded to the web, with a web stiffener if needed.
Also is it recommended that the braces align with the intersection of the beam/column or can the diagonal be connected directly to the beam with a slight eccentricity which will always avoid the issue of a column web connection? What if I use only a WT brace in the configuration I show (gamma = 90 degrees). Can the brace connect to the outer flange of the column/beam 'only' or should it align with the centerline of the beam/column width.
Also the contractor has indicated a preference for mostly bolted connections so I'm pretty sure the configuration I show will not be practical.
Thanks again.
Another question related to the configuration of lateral braces and brace connections...
My steel detailing books do not address the connection of diagonals to column webs. I have only found one online example that uses the method I illustrate here...that is using a wide flange tension/compression brace that is the same depth as the column and has a gamma of 90 degrees so that the flanges of brace and column connect directly. I realize that if the lateral loads are light that this type of brace may be oversized and there are also practical clearance considerations for W8 columns.
I'd just like to hear the thought process you guys go through when choosing members sizes/types/configuration for these types of connections. In my case the bracing loads may be light since only the top 14' of the 64' tower is exposed. In that case I would have no problem using a WT or double angle (possibly x-brace) connected directly to a gusset that is welded to the web, with a web stiffener if needed.
Also is it recommended that the braces align with the intersection of the beam/column or can the diagonal be connected directly to the beam with a slight eccentricity which will always avoid the issue of a column web connection? What if I use only a WT brace in the configuration I show (gamma = 90 degrees). Can the brace connect to the outer flange of the column/beam 'only' or should it align with the centerline of the beam/column width.
Also the contractor has indicated a preference for mostly bolted connections so I'm pretty sure the configuration I show will not be practical.
Thanks again.






RE: More Art of Diagonal Bracing
Quando Omni Flunkus Moritati
RE: More Art of Diagonal Bracing
RE: More Art of Diagonal Bracing
Take your loads and examine what your options are for bracing. I normally size in this order barring other considerations:
1) single angle for low loads with low . (sometimes look into
2) double angle once you're at a size where it becomes practical. It's generally cheaper per unit of resistance than a single angle because of the better buckling resistance.
3) WT if you're at a size where double angles aren't reasonable or they don't fit. WT sections are slightly more difficult to connect
4) HSS for larger loads due to the better buckling capacities. I generally only end up here for large trusses, chevron braces that take gravity loads or seismic applications
5) Wide Flange for some types of trusses, but they're often a pain to get good connection geometry on. They're cheaper on a per weight basis than HSS, but HSS has better buckling characteristics and I've had better luck with connections.
Generally speaking you want to optimize the weight of steel in your brace, but you don't want to do that by picking members or geometry that will require difficult connections.
How you connect will depend on how you're building it. Is it bolt up stick built in the field, is it fully shop assembled or is it modular. I don't know what you're building but it looks like something that you could at least modularize and erect in pieces. In that case, it could be weld up in the shop with some field joints.
Depending on the geometry and construction strategy it sometimes makes sense to aim somewhere other than the point where the lines of action for the other members meet but you have to take the eccentricity into account when you do it.
Is this a project where you're doing the connection design, or is it something the fabricator's engineer will do.
RE: More Art of Diagonal Bracing
With WT and single angle braces you can easily run them back to back if there's space in your bay and just put a simple spacer plate and a bolt or two at the junction point if you want the extra restraint.
RE: More Art of Diagonal Bracing
If you can put gusset plates on the outside of the brace/beam and gusset then it makes sense to use wide flanged everything of the same size and oriented in the same direction. Otherwise consider turning your brace back to gamma=0, or using double angles.
Cheers.
RE: More Art of Diagonal Bracing
RE: More Art of Diagonal Bracing
How do you configure the brace to beam/column connection when the web of the column faces inward? For a W8 column the clearance is pretty narrow for welding the gusset and I suppose you might need stiffeners somewhere if the load is high.
Thanks again for all the ideas.
RE: More Art of Diagonal Bracing
RE: More Art of Diagonal Bracing
I can't pull this from my memory banks because it is a situation in which I would not find myself. Connections are, or should be, a consideration in member selection. You might put a gusset between the beam and column, cut a slot in the diagonal, and then use clip angles to connect them. With small sizes, this may or may not be possible. The gusset would have to go in with the diagonal, it could not go first.
Bottom line use double angles or turn the diagonal 90o.
Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin
RE: More Art of Diagonal Bracing
I guess my question is not clear. The drawing I attached is just an illustration of how to solve the problem without welding to the web of the column. But this can result in oversized brace members since the brace must be the same depth as the column and beam.
I am wondering what the connection looks like when the brace is a double angle or a WT and the web of the column faces the beam. None of my steel detailing manuals (Zayat or Hayward) address this condition. Would a gusset be welded to the web of the column? My understanding is that this can be difficult weld to accomplish when the column is less than a W10 due to clearance.
Cheers.
RE: More Art of Diagonal Bracing
A couple thoughts about welding and welded connections....
If your idea that the brace be the same depth as the column or beam sections is so you can weld flange to flange, there isn’t anything real clean or neat about that either. Some of the flgs. will need a bevel prep. for welding, and there is no way to start and stop those welds without a lot of extra work. There is a good chance that those starts and stops will be left as pretty sensitive stress raisers; for lack of fusion, craters, how to terminate without back-up bars or run-off tabs, and clean-up, etc.
As for a rule-of-thumb about welding a gusset pl. to the column web, clearance to make the weld is the issue, but W10 isn’t the magic thumb. You need about a 45̊ line of sight to the welds from the inside tips of the flanges, so you can get a welding gun in there to make the weld. But, this is subject to the exact welding equipment being used, and varies a bit. Ask your fabricator what he can reasonably do with his equipment, and bag of tricks. Thus, those welds could probably be made on a W8 with a 6.5" flg. width, since d/2 (half depth) is about equal to bf/2 (half the flg. width); but a W10x60 might be tougher to do, since you are reaching deeper. Obviously, mat’l. thicknesses and exact gusset location must be included in these calcs.
RE: More Art of Diagonal Bracing
Eliminate all thought of welding the gusset to the column web. That is generally not the way it's done. The gusset plate wants to come out of the shop welded to the horizontal beams. The gusset plate would have a single or double angle connection attached to the vertical edge of the gusset that then field bolts to the web (or flange) of the column.
The connection is virtually impossible to do if you weld the gusset to the column web. If you do that, then how are you going to attach the beam to the gusset? Does the gusset get shipped from the shop welded onto the columns? That is generally not done - at least in my experience.
RE: More Art of Diagonal Bracing
RE: More Art of Diagonal Bracing
These were on 660 and 800 MW boiler house structures.
Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin
RE: More Art of Diagonal Bracing
You'll also weld up the gusset if it's something you can ship assembled or partially assembled.