Perforated Shear Wall Anchorage Between Ends

[cfox142]

We usually do a couple 3 story wood framed apartment buildings a year. I have always designed these with segmented shear walls and had hold downs at pretty much every corner and wall opening. Recently contractors have been complaining about the cost of this system. To limit the amount of hold downs I am starting to look at designing the shear walls as perforated. I have found some design examples to work through and am trying to get comfortable with this system. The only issue I have so far is trying to resolve the uplift force between hold downs. I am not asking about hold downs at the ends of the wall. It looks like I have to design the bottom wall plate to transfer tension and shear so that if I have 300 PLF at the top of the wall I need to specify a connection to transfer this load in shear and tension. This seems pretty easy at the ground floor but I can't find a good way to do this at the second and third floors. Am I missing something? How do you transfer this load?

 

[jdgengineer]

I'm confused. If you are designing either a perforated shearwall or a Force-Transfer-Around Opening shearwall you only need holdowns at the end of the wall. The force transfer around opening method has straps and blocking designed specifically to tie the wall together around the openings to behave as one single wall. The perforated wall method uses black magic to avoid the need for the straps and instead reduces the shear capacity of the wall and increases the holdown forces a bit to account for openings. In both of these options you should only have uplift at the ends of the wall.

3 story apartment, I would be using shrinkage compensating tie downs instead of holdown anchors. If you don't make sure you account for shrinkage in your drift calculations.

 

[KootK]

Am I missing something? How do you transfer this load?

Nah, it sounds at though you've got it figured out. This document describes the phenomenon and includes some tension tie down details: Link

This method is another option to be considered: Link. It can negatively affect constructability, however, depending on what is being proposed in terms of prefabrication etc.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[cfox142]

jdgenineer I am talking about the uplift forces between shear wall ends called out in SDPWS 4.3.6.4.2.1. It says to design for an uplift equal to the shear force at the top of the wall so that if I have 300 PLF at the top of the wall I need to design the bottom plate to transfer the 300 PLF in shear and also in tension. This seems to be how the perforated wall method gets around hold downs at openings.

 

[cfox142]

Kootk, thanks for the links. The first link is what started this discussion. In the example on Pg. 7 they have a uplift/shear force of 509 PLF. How can you design the bottom plate to 509 PLF of tension? I haven't ran the numbers but that would an awful lot of nails to resist that load. What am i missing here?

 

[KootK]

How can you design the bottom plate to 509 PLF of tension?. I haven't ran the numbers but that would an awful lot of nails to resist that load. What am i missing here?

As far as I can tell, you're not missing anything. It's a lot of load and a connection that essentially bypasses the sill plate may well be the way to go.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[cfox142]

I found another reference that works out the connection details of the example KootK posted. They do just use a lot of nails to make this work.

KootK - Do you reduce the uplift load by including dead weight of the wall?

 

[KootK]

KootK - Do you reduce the uplift load by including dead weight of the wall?

I do indeed.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.