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# Re: I am beginning to think that those of you using the IBC are not as swift as I thought :)

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• To: seaint(--nospam--at)seaint.org
• Subject: Re: I am beginning to think that those of you using the IBC are not as swift as I thought :)
• From: "Gerard Madden, SE" <gmse4603(--nospam--at)gmail.com>
• Date: Tue, 6 May 2008 16:50:48 -0700

Dennis,

Answer to Question 1
- You must provide 2 frames at the perimeter when your story shear is 35% of the base shear or more. So for a 1 story structure, 100% of the base shear is in the roof and you need 2 frames per side or use RHO=1.3

- In a building more than 3 stories, you may not have to have 2 frames per side per direction on the upper stories (i.e. when the story shears are less than 35%). You need to check the vertical distribution of base shear. A very heavy building with a light roof might change it to a 2 story or 3 story building, but regardless, at the lower levels of ANY building, the story shear is higher than 35% and you need to make the check or provide 2 frames.

- In all cases you can have less than 2 frames per side per direction if the elimination of the element doesn't produce a severe torsional irregularity.

- And, you do not need to have 2 braces on any side, but you must then use a RHO of 1.3. In many cases, the lateral loads are small and it won't make a lot of difference.

In a wood framed building, your perimeter walls are likely your resisting elements, so getting redundancy is usually not a problem by providing 2 walls at least. Similar with Cant. Columns. See the table for dividing shearwalls into more than one element based on the Aspect ratio.

Question 2 Answer
- Not sure what the question is, but Omega is applied whenever there is a lateral discontinuity through the load path to the foundation, that is not new and doesn't matter if you consider the diaphragm flexible or rigid.

Question 3 answer:

-The requirement for re-entrant corners and other horizontal irregularities is to design the diaphragm connection to collectors (boundaries), collectors, and collector connections for 1.25 times the force or by using Omega. Collectors in light frame construction are still excempt (see 12.10.2.1) so I believe you would need to design the boundary nailing of the diaphragm for this 1.25 increased force

hth,
-gm

On Tue, May 6, 2008 at 4:06 PM, <Rhkratzse(--nospam--at)aol.com> wrote:
In a message dated 5/6/08 3:45:37 PM, smaxwell(--nospam--at)umich.edu writes:
... IBC since 2000 and seem to be so much more advanced than us lonely engineers here in California J We really need some straight answers.

Is it really possible to use "IBC" and "straight answers" in the same sentence, with a straight face?

Ralph

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