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Crazy Connection

Crazy Connection

Crazy Connection

(OP)
Check out this crazy connection.....

RE: Crazy Connection

this is what happens when the design engineer does not design their connections. It all looks neat and tidy when it is lines meeting at a point.

RE: Crazy Connection

(OP)
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.

ConnectEngr....thoughts?  

RE: Crazy Connection

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?

We are Virginia Tech
Go HOKIES

RE: Crazy Connection

(OP)
I think it is from a power plant. A colleague sent me the picture.  

RE: Crazy Connection

(OP)
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.  

RE: Crazy Connection

Yes, I meant to say horizontal truss for diaphragm action.

We are Virginia Tech
Go HOKIES

RE: Crazy Connection

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.

RE: Crazy Connection

(OP)
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.  

RE: Crazy Connection

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.

RE: Crazy Connection

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.

RE: Crazy Connection

(OP)
dhengr:
Is that some sarcasm I sense?

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".
 

RE: Crazy Connection

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.  


More examples:
http://www.ferrellengineering.com/ferrell_engineering_022.htm   

http://www.FerrellEngineering.com

RE: Crazy Connection

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.   

http://www.FerrellEngineering.com

RE: Crazy Connection

(OP)
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 upside down

RE: Crazy Connection

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.   

http://www.FerrellEngineering.com

RE: Crazy Connection

(OP)
That would make the modeling easy...just draw it up and don't worry about beam end conditions big smile
 

RE: Crazy Connection

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.

Hg

Eng-Tips policies:  FAQ731-376: Eng-Tips.com Forum Policies

RE: Crazy Connection

I say, bring it on.  

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.   

http://www.FerrellEngineering.com

RE: Crazy Connection

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.

 

RE: Crazy Connection

I love this stuff, I did a lot of detailing early on in my career. With that background, back in the days of manual calculations, I used to send my wind and seismic diagrams to the detailer. He could check or suggest modifications to the ones that we had detailed on the design drawings, and was comfortable knowing the actual combinations rather than just max and min. I still did this with computer printouts later.

I don't know if the printouts can now show the forces for the individual load cases, diagrammatically, but I bet the detailers would like it if you sent then .

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: Crazy Connection

May seem exageration but CTE for example is asking the micropile wall providers 8 times stronger than they sell. Outlawing citizens has always amusing business for barons.

RE: Crazy Connection

Paddington
I started on the drawing board as well.  For most structural steel detailers the force combinations might cause more harm than good.  Regretfully many detailers are facing the same computer transformation.  They don't use calculators to determine angles and detail geometry.  They must lay them out to scale in CAD or model them.  They are rarely even taught engineering vocabulary. An even less about statics or basic engineering design.  Force tables are not very helpful without a basic understanding of shear, moment , and torsion.  

This said, detailing has come a long way since I had to practice with letterguides and rolling pencil.   

RE: Crazy Connection

Sorry TJ I have hijacked another thread with my banter.  Actually I really like my computer and all the software.   

And thanks for the picture.   

http://www.FerrellEngineering.com

RE: Crazy Connection

I'm most curious why the brace beams are laid weak axis to allow the flange tips to weld directly to the diagonals.

RE: Crazy Connection

SEIT, the diagonals usually cross with an opposite diagonal, (X bracing) so it is a matter of optimizing kL/r ratios.

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: Crazy Connection

It's really just vertical bracing and horizontal bracing all meeting at a column.  To me, the only thing that makes the connection appear unwieldy is the number of bolts, which off the top of my head looks out of proportion to the member sizes.  Maybe a smaller number of larger bolts would have been preferable.

RE: Crazy Connection

(OP)
Hokie-
I have a suspicion that the out-of-proportion number of bolts may be because of seismic detailing requirements (again, I defer to Connect here, hi-jack as required, I never really asked a question this post anyway). Same might be true for all the doubler plates.
My only complaint(from past dealings with these things) is some of the problems can be mitigated in these connections by simply choosing a different beam size. On a much simpler level, there has been times when I was doing powerhouse work (not working like a powerhouse) where I would be tasked to design connections for another engineers framing. There would be times when a simple pair of clip angles would suffice for a lightly loaded strut (pure axial) and the design engineer would have something like a heavy W10 or W12. My standard clips (3/8", 1/2", 5/8", 3/4" thick) wouldn't work on a beam of that depth but might have worked on W14. Again, just a simple example.
When I design my own steel and connections I try to use a little foresight; is this beam going to be easy to connect. Member design is mush simpler and less time consuming than connection design.

 

RE: Crazy Connection

Regarding the bolt size.  We typically select two bolt sizes for a project with a 1/4" gaps in size to avoid confusion in the field.  For example 7/8" A325 and 1 1/8" A490.  And a line in the sand is drawn for the cross over in bolt size.  It does appear that reasonably large bolts were used in the beam connection to the gusset plate.  If the beam connection is designed for moment, axial, and shear.  The flanges will be designed for the proportionate axial load and the flange axial load resulting from the moment couple.  This combination and the hole diameter, apparently result in an inadequate net capacity, thus the reinforcement.  If only the axial force exceeded the net capacity, then the web would also have a doubler.  "Clawed-angles" may have been another option, putting the flange bolts in double shear.  But the horizontal bracing, may have required a shear plate instead of the angles shown to fit.  But the flange reinforcement would still be required.  

Often these connections are more like a puzzle.  Tracing the forces and where the components are taken, the eccentricities, and how will it be erected.  This is art.

http://www.FerrellEngineering.com

RE: Crazy Connection

This reminds me of the connections on the New York Times building.  I only worked on a few floors, but other engineers in our office had many connections like this to deal with.  One issue driving the complexity was the need for redundancy.  The client (or perhaps the City of New York) wanted the building to remain stable if a main column is taken out.

RE: Crazy Connection

DHK
You are referring to progressive collapse and "tie forces".  This will be a requirement for many structures with the next IBC.  New York adopted this requirement almost immediately after 9/11.  We provided the connections for Building 7, the one that was allowed to burn until it collapsed.  And one of the first rebuilt.  The design requirements have been refined, but for Building 7 every beam to column was designed for a minimum axial load of 150kips.    

http://www.FerrellEngineering.com

RE: Crazy Connection

Connectegr:

By next IBC do you mean 2012?

Thanks for the warning.

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