dold
Structural
- Aug 19, 2015
- 613
Hi all,
I'm working on an upfit project where we're demoing about 2/3 of an existing storage mezzanine in a retail store. Mezz is horseshoe/U shaped and wraps around the perimeter (3 sides) of the store (see pic below - columns exaggerated). Rough dimensions are 20ft in width around the perimeter and each run of the U-shape is about 150ft. Mezz is conc slab on deck-on-bar joists-on-wideflange girders. There appears to be no lateral support (x bracing, etc) except for at the building walls as shearwalls at either end, which ends up having a pretty high diaphragm aspect ratio. However, the building columns supporting mezz are super beefy wideflanges. I'd guess (based on pictures only, site survey pending) W10x49 or heavier (all flanges bf at least as wide as depth d). Strong axis of wideflange column oriented as would be needed to resist the lateral load from mezz shaking. Further evidence would be that the columns are much heavier toward the center of the diaphragm span where trib width to each column is greater. There's also one spot over a receiving area where the mezz floor opens up a bit and there's a single wideflange column in the middle of the area that is a beast. The remainder of the building columns are just pipe columns or HSS, sized as you'd expect for a single story retail.
This leads me to believe that the lateral system for the mezz is strong axis bending of these wideflanges (essentially like a strongback). I can't find a reason why such a heavy column would be used except for giving lateral support to the mezzanine? Best i can tell, the columns don't receive any crazy eccentric loads from mezz framing, so the only bending moments would be from lateral loads from mezz. But i would expect to see a more significant connection at the roof, so as to transfer these mezz seismic loads to the roof diaphragm - i see no such connections other that typical steel framed (joist/joist girder) construction details, not detailed to perform as a rigid frame system. The framing and connections below do not indicate moment frames either.
Has anyone seen this sort of lateral system used before? What sort of system would this be classified as? Not quite a cantilevered column system, and it can't be Steel Not Detailed because this is SDC=D (at least not for current codes, building was built prior to '94.
See pics below, and thanks in advance!
note strong axis orientation perp to long span of diaphragm.
I'm working on an upfit project where we're demoing about 2/3 of an existing storage mezzanine in a retail store. Mezz is horseshoe/U shaped and wraps around the perimeter (3 sides) of the store (see pic below - columns exaggerated). Rough dimensions are 20ft in width around the perimeter and each run of the U-shape is about 150ft. Mezz is conc slab on deck-on-bar joists-on-wideflange girders. There appears to be no lateral support (x bracing, etc) except for at the building walls as shearwalls at either end, which ends up having a pretty high diaphragm aspect ratio. However, the building columns supporting mezz are super beefy wideflanges. I'd guess (based on pictures only, site survey pending) W10x49 or heavier (all flanges bf at least as wide as depth d). Strong axis of wideflange column oriented as would be needed to resist the lateral load from mezz shaking. Further evidence would be that the columns are much heavier toward the center of the diaphragm span where trib width to each column is greater. There's also one spot over a receiving area where the mezz floor opens up a bit and there's a single wideflange column in the middle of the area that is a beast. The remainder of the building columns are just pipe columns or HSS, sized as you'd expect for a single story retail.
This leads me to believe that the lateral system for the mezz is strong axis bending of these wideflanges (essentially like a strongback). I can't find a reason why such a heavy column would be used except for giving lateral support to the mezzanine? Best i can tell, the columns don't receive any crazy eccentric loads from mezz framing, so the only bending moments would be from lateral loads from mezz. But i would expect to see a more significant connection at the roof, so as to transfer these mezz seismic loads to the roof diaphragm - i see no such connections other that typical steel framed (joist/joist girder) construction details, not detailed to perform as a rigid frame system. The framing and connections below do not indicate moment frames either.
Has anyone seen this sort of lateral system used before? What sort of system would this be classified as? Not quite a cantilevered column system, and it can't be Steel Not Detailed because this is SDC=D (at least not for current codes, building was built prior to '94.
See pics below, and thanks in advance!
note strong axis orientation perp to long span of diaphragm.
