Mezzanine Lateral loads
Mezzanine Lateral loads
(OP)
Hello,
I am modelling a mezzanine with 5x1 25 ft bays. I am wondering whether this should in fact be or not braced. I was debating on the lateral load that should be placed per code and my coworkers argue that it should be .02*(TOTAL DEADLOAD) but I cannot find anything in the code regarding this [I was going to add an accidental excentricity to the columns], this in consequence arises other questions such as: "should it be placed in the center of mass of the diaphragm?" should I have besides said lateral load a given eccentricity as in the case of earthquake loads.
I would check the lateral displacements which for a 1 story mezzanine must be ridiculously small. I am in fact more concerned about the frame that's going to hold a monorail on top of the beam, the whole point of the lateral analysis is to see how it behaves, then again it's only a 1 kip load but still I'd like to see how other people approach these sorts of problems.
I've seen plenty of people modeling them in STAAD or etabs and they model the connections as rigid when in fact they are simply connected, which should increase deflections. Any ideas?
I am modelling a mezzanine with 5x1 25 ft bays. I am wondering whether this should in fact be or not braced. I was debating on the lateral load that should be placed per code and my coworkers argue that it should be .02*(TOTAL DEADLOAD) but I cannot find anything in the code regarding this [I was going to add an accidental excentricity to the columns], this in consequence arises other questions such as: "should it be placed in the center of mass of the diaphragm?" should I have besides said lateral load a given eccentricity as in the case of earthquake loads.
I would check the lateral displacements which for a 1 story mezzanine must be ridiculously small. I am in fact more concerned about the frame that's going to hold a monorail on top of the beam, the whole point of the lateral analysis is to see how it behaves, then again it's only a 1 kip load but still I'd like to see how other people approach these sorts of problems.
I've seen plenty of people modeling them in STAAD or etabs and they model the connections as rigid when in fact they are simply connected, which should increase deflections. Any ideas?






RE: Mezzanine Lateral loads
As for lateral stability, model the structure as it's idealized. If the connections are simple then model them as such. Depending on the post bases you may be able to call them fixed but you'll want to verify the anchor capacity, baseplate, and welds. On mezzanines I've designed typically this isn't hard to do.
I've seen lots of issues with improperly designed mezzanines that had little to no lateral stiffness. In addition, make sure that if you're considering the beams fully laterally braced for LTB that floor plate and not floor grating is being used. Floor plates welded to the compression flange can brace beams, floor grating with metal clips probably can as well but good luck quantifying it (to say nothing about them removing the grating).
The monorail is also something to watch out for. ASCE 7 prescribes some minimum lateral loads that I always use on a monorail, even if it's not a powered hoist. Typically 10-20% of the vertical load. This will help when they inevitably lift something off center. Pay very close attention to that cantilever, if you've never designed a cantilever monorail I have a few papers for you to look at.
Lastly, make sure your deflections are good. As you said, simple span beams will deflect more. A bouncy floor really makes people uncomfortable with loading up a mezzanine to it's maximum rated load.
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)
RE: Mezzanine Lateral loads
It's to cover lateral loads that will be imposed by people walking, moving, and etc (or at least that's how I've thought of it)
RE: Mezzanine Lateral loads
Great, if you don't mind can you share those papers on monorails, I am struggling a bit with them :)
I forgot to mention that on top of the mezzanine, we have 26 gauge type b metal deck with a 3" concrete top. So i'm taking the beams as fully braced. I ended up putting a 10K load [.02*TL at the center of mass of the diaphragm DL=50psf LL=125psf) it gave me no problems with respect to drift or anything, so i decided not to brace it. In fact the existing mezzanine which is basically a copy of the one I am making [except it was designed in 1988] has no bracing and no apparent issues until this day. Apparently it was very conservatively designed, even the point load from the column that's going to be built midspan for the monorail frame didn't even tickle the existing beam.
@ajc
I am using ASCE
RE: Mezzanine Lateral loads
RE: Mezzanine Lateral loads
Simple shear tabs.
RE: Mezzanine Lateral loads
Sponton: http://sydney.edu.au/engineering/civil/publication...
I've also attached a great paper for your cantilevered monorail.
A very good spreadsheet, though it's set for AISC 9th edition, makes a good double check and the flange bending calculations are highly useful: http://www.steeltools.org/resources/viewdocument/?...
I'd also pick up a copy of ASME B30.11 - Safety Standards for Monorails and Underhung cranes. https://www.asme.org/products/codes-standards/mono...
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)
RE: Mezzanine Lateral loads
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)
RE: Mezzanine Lateral loads
RE: Mezzanine Lateral loads
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)
RE: Mezzanine Lateral loads
RE: Mezzanine Lateral loads
RE: Mezzanine Lateral loads
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)
RE: Mezzanine Lateral loads
That is what I was thinking, but wasn't sure about the base situation. For low loads on an industrial slab, a small amount of base fixity could be designed for.
I also agree that most likely there is are some incorrect end releases in the beam/column members. Another thing I have run into, while modeling the diaphragm using plates, I have had too much stiffness when the plates were fixed to the beams. I have not used eTabs so I don't know how your diaphragm is modeled, but that could be a source of additional stiffness.
RE: Mezzanine Lateral loads
RE: Mezzanine Lateral loads
RE: Mezzanine Lateral loads
RE: Mezzanine Lateral loads
RE: Mezzanine Lateral loads
RE: Mezzanine Lateral loads
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)
RE: Mezzanine Lateral loads
RE: Mezzanine Lateral loads
Actually that's how I checked the first time but the lack of response of the system was what was worrying some. Maybe I'm overreacting, which I do quite often, but since the mezzanine is attached to existing columns, I don't want to allow too much bending to occur. (The old construction plans aren't very enlightening and the building seems to be grossly conservative.
RE: Mezzanine Lateral loads
What do you mean by response? Drift?
What is your Sds?
RE: Mezzanine Lateral loads
0.241, but the thing that I think boosts up the loads is the R-value, we have non-braced non-moment frames. which aren't even in a category. [Inverted pendulum, cantilevered column has special steel moment frames or ordinary steel moment frames..]
RE: Mezzanine Lateral loads
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)
RE: Mezzanine Lateral loads
I don't know what that is.
That said, tension-only braced frames are the most efficient lateral frames - is there any chance of using cables or rod, or will walls and doors/windows get in the way?
How about just kickers to brace?
RE: Mezzanine Lateral loads