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Steel Moment Connection Design 3

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sbaldy

Structural
Jun 5, 2003
1
I have a project designing steel connections. The EOR is specifying reactions for steel beams - as is typically done. There are also several moment connections specified with a triangle symbol without any design moment specified (also typical).
Normally if the moment connection is between a WF beam and a WF column, I would try and develop the full moment capacity of the beam or column, whichever has less capacity. But in this case the WF beams are supported from the side of HSS columns with welded moment plates on the top and bottom flange of the WF beam (no room for collared plates). In this case the HSS column has a much lower moment capacity and the allowable moment is further limited by the compression plate into the face of the HSS column.
Just curious what other engineers would expect for design of these moment connections?
 
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If I am running into issues I occasionally will submit an RFI to the EOR with the capacities I can get with my preferred assembly and ask them very nicely if the capacity is high enough or if they can please provide a design moment so I can sharpen my pencil. I usually preface it with "In the spirit of providing the most economical connection..."
 
Not providing moments may be typical, but it's also wrong.

Submit an RFI requesting the design moments from the EOR. If they give you any lip, quote the Code of Standard Practice for Steel Buildings and Bridges, 3.1.2.
 
Both short but great pieces of advice above.

phamENG said:
Not providing moments may be typical, but it's also wrong.
This 100%.

IMO there is plenty wrong with the designing engineer in steel not designing (or at least substantially considering) the connections. As an experienced steel designer the often determines the member size/type. The is especially true for moment connections where it is often economical for a larger member to be selected so that it reduces or removes the need for web doublers, flange doublers, or even sometimes web stiffeners. The fabrication costs for these type of connections sky rocket quickly.

sbaldy said:
But in this case the WF beams are supported from the side of HSS columns with welded moment plates on the top and bottom flange of the WF beam (no room for collared plates).
I've delved deeply moment connections into HSS columns recently. Things can get tough pretty quickly, though you probably already know that. I found IdeaStatic a fantastic tool to test out various designs quite quickly. I hadn't used it previously as my other tools have been sufficient. (I had to google what collared plates where, they can get seriously sophisticated(expensive) quickly.

sbaldy said:
Just curious what other engineers would expect for design of these moment connections?
How long is a piece of string. It really depends on the structure. Sometimes my moment connections need only a small fraction of either member capacity. Other times I am well over 50% and occasionally 100%.

 
Like phamENG typed send an RFI to get the beam end moments.

If I am in a big hurry and the RFI is coming back too slowly, I'll typically compute the largest moment that will work. Add a highlighted note to the calc package asking the EOR to verify the end moment isn't higher than that. I can't recall a time when I did that and the EOR came back with a higher moment.
 
I did not do the design for the steel connections, but I recently saw a set of plans where the EOR delegated beam to girder shear connections to be designed for "a minimum of 150% of the maximum beam end reaction indicated by the AISC max total uniform load tables." That's a lot more than I've ever seen as a general note. Have any of you seen something like that?
 
RPGs said:
I did not do the design for the steel connections, but I recently saw a set of plans where the EOR delegated beam to girder shear connections to be designed for "a minimum of 150% of the maximum beam end reaction indicated by the AISC max total uniform load tables." That's a lot more than I've ever seen as a general note. Have any of you seen something like that?

That's a new one on me. Any chance these are composite beams? The EOR might know that the UDL approach is unconservative for those.
 
271828 said:
Any chance these are composite beams?
Exactly my thought, but it threw me because the note specifically called that out for "Connections for non-composite beam to girder connections".
 
Well...designing a beam end connection that (theoretically) transfers only shear for a value based on a theoretical maximum moment is a bit backwards to begin with. If everything is uniformly loaded all the time and has a relatively long span then...sure...it works out in the end...but any short beams or concentrated loads near the end of the beam? Those values can diverge pretty quickly.
 
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