Any good references for design of a CMU building with a second floor on only half of the building?

[ivanga7]

I am working on a project where a CMU building will have a second floor on only one half. I have a rigid diaphragm at both the roof and floor levels. I am not quite sure how to distribute the forces to the walls where only half of it is resisting second floor loads. I am particularly having a difficult time determining what wall rigidity to use for resistance at the roof and floor level. Please see the attached quick sketch for reference.

http://files.engineering.com/getfil...795c-4ca5-b626-78f89a5985c9&file=scan7318.pdf

 

[dik]

The taller walls have to be laterally supported either horizontally or vertically.

Dik

 

[Mjkkb2]

if you're asking about the lateral loads (stability design), then it all depends how you're designing the two story wall to span. It can either span from grade to roof (vertically) or between the building sides - horizontally.
IF vertical model is assumed then the tall wall will distribute half it's vertical exposure wind load to the roof and the other half to the ground.
IF horizontal model is assumed then the loads will distribute to the vertical walls (N and S) if you're evaluating the W wall wind.

 

[msquared48]

Amrhein...

Mike McCann, PE, SE (WA)

 

[ivanga7]

Mjkkb2 I understand the concept for the out of plane loads, but what is confusing me is the distribution of the seismic diaphragm loads. The taller wall resist diaphragm load from the roof but none from the floor level? Also when doing my roof rigid diaphragm analysis, do I consider the rigidity of the entire wall, or only the piers that will be resisting roof load (tall pier and pier on second floor)? I hope this makes sense.

 

[jayrod12]

The taller wall would in the end resist the second floor loads unless you provide a full height joint where the second floor ends.

 

[Mjkkb2]

Assuming the wall has no joints (one long shear wall) I would assume the whole length and whole height for the rigidity calcs for the roof diaphragm.
For the floor diaphragm I would assume the ground to floor as height and just the half length (where connected to floor) as length.
SO in other words ; for roof use the whole wall length and for floor use just the shorter pier length.

If you put in a joint (which is acually not a bad idea) where the floor ends then you'd have two independent shear walls. The tall one will only carry a portion of roof shear and the one at the floor will cary roof and floor shears. The rigidity will also be simpler to model...

 

[ivanga7]

Mjkkb2, I will have a joint. For the roof shear, I should also consider the rigidity of the wall that spans from floor to roof in addition to the rigidity of the tall one, right?

 

[Mjkkb2]

yes, I would.

 

[ivanga7]

Thanks for the help!