Alternate Braced wall panel (IBC 2006 2308.9.3.2)

[jeffhed]

My question is simple. I have engineered quite a few houses with 2'-0" wing walls on either side of the garage door. these garages almost always were 7'-0" tall doors, so my shear wall aspect ratio did not exceed 3.5:1. However, over the last couple of years, these homes are being built with 8'-0 tall garage doors, which exceeds 3.5:1 aspect ratio. IBC 2308.9.3.2 shows an alternate braced panel that would work great for these walls. However, I am in seismic design category 'D' and am skeptical this can be applied in my area since the braced wall panels table (IBC 2006 table 2308.9.3(1)) only goes up to seismic design category 'C'. Am I understanding this right? It just seems like I am the only one specifying strong walls at the front of the garages that don't meet the aspect ratio criteria. Although I don't think this is an option in my area, I would like others insight on when this detail could be utilized.

 

[MiketheEngineer]

I believe you are right. Have you looked into Simpson's "Strong-Wall"?? Those should solve your problem and I beleive they are appropriately rated.

 

[jeffhed]

Yes, I have. I actually spec iLevel Shear braces as they are cheaper and provide the same shear resistance as the strong walls. I just wanted to see if I was missing something in 2308.9.3.2 that would allow me to use the alternate braced wall panel in lieu of a strong wall or shear brace because it seems I am the only one specifying them where on these garages.

 

[MiketheEngineer]

You probably are - since the local code bullies haven't caught up yet.

 

[msquared48]

I believe that if the shearwall is a rated and tested system, as is the Strong Wall, the aspect ratio limit does not apply.

It does apply if the wall is constructed from scrfatch in the field as a normal plywood shearwall.

You know, to get back into the aspect ratiuo limits though, all you have to do is raise the height of the concrete stem pall below the shear wall.

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

 

[jeffhed]

msquared48,
You are correct, with the strong walls or shear braces being tested systems, the aspect ratio does not apply. I spec the strong walls when I have walls at the front of the garage that don't meet the aspect ratio. 99% of the time, the shear forces are well within the shear strength range of site built shear walls, the strong walls are ONLY specified to meet the aspect ratio. The taller concrete stem wall is also a good idea. I have mentioned this to contractors before and they act like I gave them an alternate option of building the foundation out of moon rock. I think the taller concrete stem wall seems really easy, but only a handful of contractors have wanted to do that. I do not have much experience in construction, so maybe there is a reason beyond what I can see why this extended stem wall is a problem. In the end I think I was hoping for a little "magic" or hidden exception in the code to save me the "we've been doing it this way for years" excuse for not reading the plans. Sigh.

 

[msquared48]

As opposed to using the Strong Wall, which is much more expensive than using normsal shearwall framing, most of the contractors I have dealt with over the years preferred to raise the stem wall. Interesting.

Where are you?

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

 

[jeffhed]

I am in Southern, Utah. Down here, code has just been a guideline more than the rule until about 6 or 8 years ago. Contractors are resisting the changes less and less, but still resist these "new" code requirements. I think the biggest resistance to the taller stem wall is that the concrete guys will have to actually look at the section details and can't just do whatever they are used to. If its going to be different, chances are it won't get done right anyway. With the Ilevel shear braces typically costing around $300 - $400 a piece, I would think you could do the stem wall too short, tear it out and redo it for less than the cost of a couple shear braces. But, I give them the options and they typically pick the shear braces. Go figure.

 

[msquared48]

Could also get into a small additional pour issue.

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