Opinions on Reason for Moment Connection

[TEDstruc]

I have a situation where I am being asked to remove (or relocate) several column posts from a mezzanine in an industrial plant setting. The mezzanine is made up of posts from the floor at about 25 foot spacing in both directions. The Building Columns are at 50 foot spacing in both directions and the mezzanine posts sit between the building columns. The mezzanine beams tie into the building columns. At all of the posts in between columns, the mezzanine beams are connected to the posts with robust moment connections, and I'm having trouble coming up with a reason the engineer did this. The only thing I can really think of is that they did this for deflection control. I don't think the mezzanine was designed with the building, as part of the lateral force resisting system.

Any opinions would be appreciated.

Here is a screen shot of the mezzanine steel layout, with an example post that has the moment connection circled in red.

I'll add another view of the connection at this location, in my next post



Thanks

 

[TEDstruc]

Attached is a screen shot of the connection at the top of the post

 

[TEDstruc]

And here is an actual picture of the connection

 

[WARose]

With the information given....it's hard to say. I doubt it was for deflection control. Usually (with steel) you get enough rotation at the joint to where it's not that big of a impact as far as deflection goes. (And usually a deeper beam is more cost effective.)

The only things I can think of: it originally was the LFRS, they were thinking of using some sort of trolley on the beams, or perhaps, in the absence of a diaphragm/plan bracing (neither of which appear in the pic you show), the "moment" connection acts as a drag strut to get it to the LFRS. The old timers did that a lot.....they didn't like transferring axial load through web connected angles. Another possibility it's for some localized condition/piece of equipment that needs its own LFRS.

 

[EZBuilding]

Maybe it's an attempt to resist minimum stability forces, ASCE 7-10 1.4.3?

 

[SlideRuleEra]

The mezzanine beams tie into the building columns.
I don't think the mezzanine was designed with the building, as part of the lateral force resisting system.

Perhaps to keep the mezzanine from transferring it's on lateral loading to the building columns (whose lateral load capacity may have been unknown). And doing this without any bracing to clutter the space under the mezzanine.

http://www.SlideRuleEra.net

 

[msquared48]

I agree with sliderule.

The mezzanine may have been designed and installed after the building was designed and erected.

Mike McCann, PE, SE (WA)

 

[TEDstruc]

SlideRule and Msquared,

That makes the most sense to me. Thanks for all of the replies.

 

[FloydLloyd]

I agree that the mezzanine should be self supporting for lateral forces.
Reference: ASCE/SEI 7-2010 and 2016, Chapter 15, Seismic Design Requirements for Nonbuilding Structures.
I reviewed a "big box" store a few years ago where there was damage to walls from unrestrained rack structures which transmitted seismic forces to non structural partitions, and masonry infill walls.

 

[JAE]

Do the beams work for the original mezzanine loading? Perhaps used to keep the moments to a level where the beams work with light storage live load or something.

I note that the photo shows empty bolt holes - where an end plate moment connection was originally intended but abandoned for the welded plate connectors.

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[KootK]

Is there any discrete horizontal bracing in the floor deck? Often, bar grate is deemed to posses no diaphragm capacity and, thus, framed joints not aligned with primary columns would need to be internally stabilized like this.