Holddowns at multi-level wood shearwall design
Holddowns at multi-level wood shearwall design
(OP)
Hi all, this is my first post here! I couldn't find a topic specifically pertaining to this, so I decided to make a new thread for it. Basically, I am wondering how those of you who do a lot of wood shearwall design handle overturning forces, primarily when it comes to tension. When I have a single story structure, or even a two story structure, I just use segmented shearwall design. If there happens to be a tension force I need to design for, each shearwall end post gets its own holddown at the foundation level. This means that if a tension force from a shearwall above does not land directly over the shearwall end post below, then both shearwall end posts receive their respective holddowns at the foundation level (rather than relying on the strap above to transfer the tension load out to the end posts of the shearwall below).
Once a third story comes into play, however, and especially when the wall segments have end posts that do not align with the segment end posts below, I have a huge smattering of holddowns all over my foundation stem wall! At this point, do you guys and gals switch to a perforated shearwall design to keep the tension strapping to the ends of the entire wall elevation? Or do you stick with segmented design and determine that the shearwall panel below transfers the tensile overturning above out to the end posts of the wall segment below?
I'd love to hear your thoughts on this, there is a HUGE amount of book keeping that needs to happen once that third story comes into play, and I would really like to simplify my approach as much as possible. BTW I do primarily residential design here in Seattle.
-Brice
Once a third story comes into play, however, and especially when the wall segments have end posts that do not align with the segment end posts below, I have a huge smattering of holddowns all over my foundation stem wall! At this point, do you guys and gals switch to a perforated shearwall design to keep the tension strapping to the ends of the entire wall elevation? Or do you stick with segmented design and determine that the shearwall panel below transfers the tensile overturning above out to the end posts of the wall segment below?
I'd love to hear your thoughts on this, there is a HUGE amount of book keeping that needs to happen once that third story comes into play, and I would really like to simplify my approach as much as possible. BTW I do primarily residential design here in Seattle.
-Brice
RE: Holddowns at multi-level wood shearwall design
RE: Holddowns at multi-level wood shearwall design
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.
RE: Holddowns at multi-level wood shearwall design
I may just need to do a free body of a mid-wall strap. The strapped studs of course will receive panel edge nailing in addition to the strap nailing. It would really be nice to be able to use the full length of a wall segment without having to put so much hardware in at the lower level. It seems that perforated shearwalls are not a popular approach?
RE: Holddowns at multi-level wood shearwall design
RE: Holddowns at multi-level wood shearwall design
I drew a free-body diagram, and it seems that if you place a strap in the field of a wall, and provide panel nailing at the strapped stud, you will increase the shear in the wall by T/(2*H) where T is the tension force, and H is the height of the shearwall. I may just start beefing up my shear panels to meet the extra capacity required and not put the additional holddown below.
My main issue, as stated above, is confusing the residential contractors I work with by trying to force things to align. Obviously, they will know where the end of the wall is above because they HAVE to know where the windows go, and those dimensions are readily provided in architectural documents.
If someone has tried the method of increasing required shearwall capacity by T/(2*H) please let me know, or if I'm way off please also let me know why, I would really like to hear your thoughts and hopefully simplify the residential design approach among those of us who do this work!
Thank you
RE: Holddowns at multi-level wood shearwall design
I try to get holdowns to line up as much as possible, but sometimes that doesn’t work. In those cases, I have a typical wall elevation detail showing holdowns that don’t align. Developing typical details like this for perforated, segmented and force transfer shearwall can save you some time.