Wood Perforated Shear Wall

[kotichaz]

Hey all,

I have a couple of questions regarding the perforated shear wall method. I would really like to implement this method more often in my designs but have a few issues that are bugging me.

1.) Does anyone apply dead load to resist overturning moment using this method? I have been unable to find any design examples that show how to apply the dead load to the wall. I have typically been ignoring dead load due to this but would like to implement it into my spreadsheets.

2.) Per the SPDWS2021:

"3.6.4.2.1 Uplift Anchorage for Perforated Shear Walls: In addition to the requirements of 4.3.6.4.2, per-forated shear wall bottom plates at full height sheathing shall be anchored for a uniform uplift force, t, equal to the maximum unit shear force induced by the design load, νmax, determined in 4.3.6.4.1.1, or calculated by rational analysis. "

Does anyone have any recommendations on how to handle this? Can I use the dead load on the wall to resist this effect? I am wondering what type of connections to use for this condition, especially for multi-story buildings. I am concerned that contractors will ignore whatever I specify to resist this uplift.

Thanks for any suggestions.

 

[DaveAtkins]

I typically include dead load, multiplied by the appropriate load factor.

DaveAtkins

 

[L_Bey]

The perforated tie down requirement is a bit tricky, since it's the one thing that really differs from the standard wall framing. In my experience, typical sill anchors are generally OK for the uplift load at the base, though the spacing might need to be dropped depending on how heavy the loading is. At upper floors it's not quite so simple, since anchoring the wall above to the wall below along the whole length is not typical construction. I think the last one I did we used one of the long simpson framing screws between the bottom plate of the upper wall and the top plate of the lower, spaced at 12" or 24" on center, to account for that requirement.

I do not reduce the code required uplift anchorage along the length of the wall by the dead load. My reading of the code has always been that the anchoring requirement is separate from the overturning stability of the wall, and is related to the testing set up that generated the perforated wall requirements, so reducing the uplift anchorage for the dead load would not be permitted. But I think you could argue that the "calculated by rational analysis" section would allow you to use load combinations there. I definitely do use the weight of the wall and any supported floors in the overturning calculation for the holddowns on each end however.

 

[kotichaz]

Thank you all for the responses. I glad to see there are people using dead load to resist the overturning moment. When calculating the resisting moment, are you guys using a uniform dead load across the entire length of the wall? Or are you applying the load only to the sum of the lengths of the full height segments?

Thanks once again.

 

[DaveAtkins]

I use a uniform dead load across the entire wall length.

DaveAtkins

 

[L_Bey]

The big benefit of perforated shear walls over segmented is that you can look at the entire wall, including openings. With a segmented shear wall each panel stands on it's own, meaning that the overturning/uplift calculation is for each panel alone. With a perforated wall you can run the overturning for the full wall which will greatly reduce the amount of overturning and the loads to the holddowns. For a shear wall with two windows, using the perforated method would result in 6 holddowns whereas a perforated wall would result in 2. However you do need to meet the tension tie requirements from the code, so there is a trade off there. See attached for a sketch of the options.