Shearwall Rigidity - Explanation and Example 1

[P1ENG]

I took yesterday to wrap my head around shear wall rigidity. I don't normally engineer buildings that require shear distribution per wall rigidities because I normally assume flexible diaphragms. However, sometimes I have a building that does not have a wall with a shear wall due to aspect ratios or large openings, and I am left with a "3-sided" building. Therefore, I educated myself on rigidity.

You can find my explanation in the attachment below. Somebody let me know if there are any mistakes. I am assuming wood shear walls.

The method, not necessarily the equations, are the same for other lateral force resisting systems (steel frames, masonry shear walls, concrete shear walls, etc.)

Juston Fluckey, E.I.
Engineering Consultant

 

[RFreund]

At first glance this seems reasonable and it depends on how picky you would like to be. Some additional info for wood:

The deflection of shear walls can be found using either a 3-term or 4-term equation that accounts for flexure, shear, nail slip, and holddown deformation.

3-Term see here:

http://www.awc.org/pdf/2008WindSeismic.pdf

4-Term is listed in a few places include IBC but also see here:

http://www.apawood.org/level_c.cfm?content=pub_searchresults&pK=l350&pT=Yes&pD=Yes&pF=Yes

Using these equations you could get the relative stiffness.

To simplify for Masonry, Concrete and Wood if the walls are the same height then I would just use Length to get a reasonable estimate as you have shown.


EIT

 

[P1ENG]

Good call on the other terms that can account for shear wall deflection. The file I attached is limited to considering only flexure and shear deflections. I actually stated this at the beginning of the document, so it is important to note that care should be taken to verify all the assumptions I made. Thanks for having a look.

Juston Fluckey, E.I.
Engineering Consultant

 

[msquared48]

I agree for the wood shear walls with the comment above.

As for masonry, the best examples I know of for a rigid diaphragm analysis are in Jim Amrhein's book, "Reinforced Masonry Engineering Handbook", pages 203 through 226 - a design for a seven story masonry apartment building.

If you can get your hands on a copy, check it out and save it for future reference.

Mike McCann
MMC Engineering

 

[HuckleberryFinn]

+1 for the Amrhein comment, the tabulated rigidity values for masonry shear walls are just plain handy.

I would also reccomend you check out the old army guides, they have some really good explanations and presentation of design material in there. They are also free.

Check this out (Start reading around Chapter 7):

http://armypubs.army.mil/eng/DR_pubs/DR_a/pdf/tm5_809_3.pdf

Funny story about engineering books. Generally I've found that the older the book, the more it makes sense and isn't asinine. Just my two cents.

-HF

 

[asixth]

I agree with the logic of the publication that you posted. For diaphragm stiffness you may also want to look at Naheim's (ed.) book on seismic design.