Design of Irregular Wood Diaphragms

[rodan2000]

I cannot find a decent enough reference that covers my situation with this irregular diaphragm. Here is the layout of the diaphragm with shear walls along A/B and 1/2 (note they aren't full length but we'll ignore that for now):

A B
| |
_____ _1
| |
_ |_ |__
| |___| |
| |
|___________| _2


The loads to the diaphragm are small. I know that if I throw in some perimeter edge nailing (PEN) along the reentrant corners, it'll be fine because the loads are so low. Yet, I do not feel I can justify this design with numbers or accurate analysis. I know there are some assumptions I can make that would produce an overly conservative design but I still want to be able to understand how this diaphragm will perform.

Most of the references I have or found (Breyer Wood,

http://soe.uaa.alaska.edu/soe/courses/ce434/docs/Lects/HorizDiap2.ppt)

only get into L shapes, Z shapes, and simple openings within a diaphragm.

I have also thought about buying this but I'm not sure if it would help:

http://www.atcouncil.org/Design-of-...f-Horizontal-Wood-Diaphragms/flypage.tpl.html

If you know of a reference or have any suggestions on how to approach this, I would greatly appreciate it.

 

[msquared48]

Break it up into rectangular sub-diaphragms with drag struts and associated shear walls/frames.

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

 

[frv]

As usual, Mike is right.. just use drag struts to get your shear into your shearwalls.

 

[rodan2000]

I guess I'm not sure how to split it into sub-diaphragms. I have two cantilevered diaphragms with an unusual opening placement while having awkward shear wall placement as well. I cannot wrap my head around how to break this up into something manageable.

I know how to take care of the cantilever to the right of Grid B: a collector force diagram with the unit shear from each side and the wall shear below. Typical.

The cantilever between A and B is giving me the hardest time. In the transverse direction (vertical on the page), I'm not sure how or where the shear from the cantilever will go: to shear wall A or shear wall B because of the discontinuity at that opening?

Also, once I get that figured out, I'm having trouble determining where my chord forces will end up: at the opening where the diaphragm has a small cross section or all the way up to grid 1 or somewhere near the opening?

 

[msquared48]

In regards to breaking it up, just add internal vertical and horizontal line extensions to those already existing until all you have are rectangles. Then see which ones you can develop with drag struts and links to shear walls or frame locations.

As for the cantilever to the right of Grid B, there is a size limit by code as to the area you can cantilever. You may need to add a steel frame at what would be grid "C", which is unmarked.

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