Vertical Distribution

[SalDorado]

I am working on a structure that has a landing/second floor at 14'-6" above finish floor and a roof at 26'-0'. The landing/second floor is on one corner only, it is not the full width and length of the roof plan area. Also, the floor/landing is being supported by hangers from two sides and connected two the walls on the other two sides. Laterally the floor/landing has a shearwall on one side supported from the roof and it is connected to a full ht shearwall on the other side. Is a vertical distribution of seismic forces required?

 

[msquared48]

So, as I understand the framing, the wall studs will have to take any torsional forces that will be distributed to the roof diaphragm. If anything, additional forces will be distribted to the roof, not the mezzanine, so do the distribution.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[rscassar]

Are the shearwalls oriented in the same direction or are they perpendicular to each other. This sounds like an intricate detail. Has the roof been designed for the "hold-down" force of the boundry element for the shear wall. In terms of lateral distribution, I would ensure that the mezzanine is laterally braced in both directions and distribute the mass to the roof which it is being hung from.

 

[Den32]

Does a 'mezzanine' count as a 'floor' in seismic calcs? What about a catwalk system? I recall looking for this answer in the code (ASCE 7) without any luck.

For your seismic load distribution, seems like a 'mezzanine' or 'catwalk' system should be treated as a 'Non-structural' component and not considered a floor. This would change how the seismic loads are distributed.

I am not in a high seismic region, so just my 2-cents

 

[msquared48]

Den32:

If it is a catwalk, yes, but the weight still has to be added for the seismic.

If it is a mezzanine that is self supported laterally, totally separate from the rest of the structure, then yes again - no redistribution needed.

However, that does not appear to be the case here as the mezzanine is attached to the structure, and has shear walls only on two sides. Here I would redistribute.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[BAretired]

The floor does not seem to be well restrained against torsion. I would be concerned about a pendulum-torsional effect with the floor rotating about the exterior corner where the two shearwalls meet.

BA

 

[MiketheEngineer]

I hate to be a party pooper - but don't you need landings every 12' of elevation - IBC 1009.6

 

[rscassar]

With any seismic calculations or dynamic analysis it is essential that all mass is accounted for in the design.