Perforated shear wall at garage

[jeffhed]

Every once in a while I have a residential project where the front of the garage could be analyzed as a perforated shear wall. i.e. The walls at the side of the garage door meet the height-to-width ratios and the Co number doesn't get too low so the shear wall nailing and sill plate uplift is reasonable. I have always chickened out in the end and used the segmented shear walls. Has anyone else ever designed the front of a garage as a perforated shear wall on a residential project before?

 

[EngineeringAdam]

My office is involved in many small residential projects that involve needed shear resistance at the garage.

We have not used perforated design for garages because the opening doesn't have sheathing above and below the opening, and according to the ANSI SDPWS-2008 perforated shear walls need sheathing above and below the opening - at least that is how I interpret it.

Force transfer around openings might be able to be used at a garage, but typically we either use shear walls or shear panels at the garage.

I work in California in a Seismic area, so using shear panels is not uncommon at the garages we engineer.

 

[jeffhed]

EngineeringAdam,
You can do perforated shear walls with a doorway in the middle. See Table 4.3.3.5 in the SDPWS-2008. The table shows shear reduction values for opening up to the full wall height. However, the problem with large openings we usually run into is high sill plate anchorage forces, that begin to force you back to a segmented approach or the force transfer method. The shear panels on each side of the garage is not uncommon here either. Just for fun I check to see if it would even work as a perforated shear wall. Once in a while it does, although as I stated before, even when the numbers work I have still used the segmented approach.

 

[MiketheEngineer]

Or you can use the Narrow APA wall or the Simpson product that does the same

 

[jeffhed]

MiketheEngineer,
I was wondering about using the perforated wall to eliminate hold downs. The narrow APA wall or the simpson strong wall would require the same amount of hold downs. I am in seismic design category D here, I am under the impression that the narrow APA wall is only for seismic design categories A, B and C, so we don't use that much.

 

[EngineeringAdam]

Jeffhed, forgot that table 4.3.3.5 covers full height openings - good find. Well, I guess since you know you can do why not just do it?

 

[MiketheEngineer]

I do believe you will need hold downs of some sort - and I didn't know you were in "D"

 

[jeffhed]

EngineeringAdam,
Its kind of hard for me to swallow looking at the front of a garage with only two hold downs instead of 4. Just looks weird. Maybe I'm a little too paranoid, I don't know. The numbers work, just wanted to see if anyone has used it before to try and make myself more comfortable with it if I can use it in the future.

MiketheEngineer,
Yes, I would probably need at least two hold downs unless I had quite a bit of gravity load to resist the overturning, which in my experience would be rare. We can get into to "C" once in a while, but most times we are in "D". There are plenty of times I would love to use the APA narrow wall, but just cant'.

 

[msquared48]

If you use a glulam beam over the garage door and extend it to the exterior walls, connecting the shear walls to the beam, you can get away with two holddowns at each end of the beam at the foundation level, and two strap ties at the top of each shearwall where they connect to the beam.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[jeffhed]

msquared48,
So you would be strapping the garage header to the wall to make it a fixed connection at the top of the wall? Then you are looking at the front of the garage and providing hold downs for the whole panel overturning?

 

[msquared48]

Yep.

The proper connection of the beam to the shear wall(s)allows you to use smaller holddowns at the extremeties of the beam at the foundation.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com