Cylinder shear? 1

[ctmtwilliams]

Today I was having a discussion with a neighbor while looking at his addition to his home. The neighbor designed the addition and it has some unique design elements. The one element which stands out as being the most obvious is that it is basically a three story cylinder roughly 25 feet in diameter. The structure is conventional stick framed with engineered wood floor joists and beams. Due to the circular layout, the spacing of windows and "sheer wall" became an issue, with the width of the "sheer wall" losing out to the spacing of the windows by the contractor. The county is requesting that the neighbor have his structural engineer re-calculate using the “final” (as built) sheer wall widths. Being a geologist and not a structural engineer my question is this: Is there really sheer concerns with a cylinder shaped building? I thought the sheer wall was to prevent the building from “racking” during earthquakes, high winds, or other unusual heavy side loads. They only way I can visualize a cylinder needing sheer would be if it has some twisting or rotational load applied. Thoughts or clarifications?

 

[14159]

The building officials are correct.

Resistance to wind and earthquake loads should be checked for this structure. The only relevant difference between this structure and a rectangular one is the lack of an obvious pair of principal directions. To design the shear walls, the engineer should investigate lateral loads in any direction. This will be easy if the layout of wall panels is symmetrical around the perimeter because all directions will either have identical or similar results.

The main questions are the same as for any other wood shear wall building:
1. Is there enough length of shearwall to resist the loads?
2. Do the shear walls have a close-enough nailing pattern?
3. Are the shear walls held down to resist overturning?

Almost got me on my soapbox about non-engineers designing stuff. My immense discipline was barely enough to avoid a rant!

Happy digging to you!
DBD

 

[ctmtwilliams]

Thanks for the reply DBDavis! Also, thanks for pointing out the difference with the lack of obvious principle pair directions. And you are quite right, I think this is why professionals must be included in these types of projects!

Regards,

Craig