that, and I have run into it plenty of times when a nice FEM model gives a beam size that works, and an engineer uses it without regard to how to connect it.
This happens A LOT.
I don't think that the connection looks bad by any means. Although I agree adding member depth and flange width while detailing helps.
Toad:
What framing is this or did you randomly stumble on this? It looks like fin plates welded to a column flange and receiving the brace and beams. It appears to be braced frames in both directions and some sort of horizontal bracing diaphragm?
Slick-
Power structures like these don't really have a diaphragm, just horizontal bracing (I think that is what you meant).
I'll tell you, and maybe I am just a dummy, but these connections are extremely difficult to design. It takes a lot of time and effort.
I've been forced into connections like that on power plants and oil refinery structures, once or twice by circumstances, and once or twice by "executive decisions" made by bosses. I always showed the approximate detail on the design drawing in the hopes of getting changes, but it didn't work. At least, it relieved the detailer of the responsibility.
Michael.
Timing has a lot to do with the outcome of a rain dance.
From my experience, a lot of times what happens is, these beams have very little or no vertical loads, so they are beam-columns and really just columns. The model will spit out a shape that is befitting a column, like a heavy W14.
Then comes connection time and they become hard to connect due to extremely high axial loads.
I really would like to hear what ConnectEngr has to say.
The connection looks pretty good to me. It's a heavily loaded joint, for sure, but I'd say the connection engineer did a good job with what he had to work with.
Looking strictly at this joint, not knowing what else is going on, one could make the following suggestions:
The wide flange diagonals in the vertical braced frame could be turned with their web vertical, so that they could be connected with claw angles to the gusset, like how the horizontal member in this plane is connected.
The wide flange diagonal in the horizontal plane, connected with angles on the web, could be changed to a double angle member (or four angle), although it might be hard to achieve the required member capacity this way.
Toad:
Hell, with a little finesse, there is room for another 6 or 8 members to frame into that joint. CAD and FEA can do anything and everything. If you chase those loads, forces and reactions around enough, you finally lose them and can forget about them.
Reminds me...My father used to say to his sales guys "if you chase the job long enough, you're going to catch it".
I know sometimes these connections are a necessary monster....but I have been forced into them a few times because along with our design assignments we were handed mill rolling schedules so as to say "here you go, these are the beam sizes you can use this week".
I think the connection engineer worked out a difficult condition (IMHO). We see a lot of this in power house work. The columns are usually very large with large bracing loads. With no diaphragm, horizontal bracing loads are also large. We have projects with moment connections and bracing at each joint. Add to all of this, the galvanizing. So all the connections are field bolted and Class A(C) Slip-Critical (even more bolts).
We designed similar connections for a cement plant in Costa Rica, with every beam moment connected and braced vertically and horizontally. 4 moment connections and 16 brace connections at each column grid. Initially they were field welding everything. They had a beam line, but did not trust it's accuracy. Due to obvious construction delays, we were called. We convinced them to trust their beam line equipment, and introduced them to Ken Lohr and tension control bolts. The remaining 5 1/2 stories were completed faster than the first 1 1/2.
Thanks for the picture TJ. I love this stuff. I wish they all looked so fun.
TJ
You are correct with the beam sizing. There is very little shear, so the beams a simply axial loaded struts. Beam end rotation is not an issue. But the beams are generally "column size" in depth and weight.
Connect-
How does one handle design of a lateral system with moment connections and bracing combined? Is the bracing there for secondary forces?
IMHO, the design of these connections is very trying to say the least. Until one embarks on such a design he may not understand just how difficult it can be.
Then again, I may just be a dummy (-:
Moment connections with bracing is another of those gifts of modern computer models. Similar to the recent thread about rigid truss joints. Sure the joints are probably not flexible anyway, why not model them as fixed. The connection engineer can figure out how to combine the axial and moment forces. Gotta love this job.
That was something that bothered me in school. Everything we did was lines and nodes. I asked how this stuff actually gets connected. I was given a booklet about the AISC Connection Sculpture.
Let the software do all the thinking. Why should an overworked and underpaid engineer, second guess a computer. "If it wasn't practical, the software wouldn't allow it". Go ahead, it wouldn't be call "optimized" if the sizes weren't the best choice. Nucor makes all those different sizes for a reason. Print out the fancy analysis, load case combinations, and the cool 3D renderings. Make um all fixed and braced. Show the envelope forces on the contract drawings. And close your eyes...
This is just more work for me. I am confident that in most cases I can design a connection for the forces and interactions. BUT, there is no guarantee that anyone will be able to afford the design, fabrication, and erection costs.
by the way...
I don't think your picture represents this type of thinking. We frequently see those connections in industrial framing with axial forces (no moments) and an open channel to the designer to discuss all options.
May the force be your companion ... we may resume a modern code in say do it as thick as you can and fit every kind of item you can put. This must be good for business.
