Wood shear wall question
Wood shear wall question
(OP)
Wondering what others thoughts are on this one. I have a 15' tall x 15'-8" wide wood sheathed wall for a commercial building that has 2 large openings in the middle (door + window above) essentially leaving only 3'-10" wide legs on either side. The height exceeds 10' to address as a conventional portal frame wall and the aspect ratio of the legs is greater than 3.5:1. The in plane loading is relatively light.
Would seem that an engineered solution is certainly possible as a portal frame (2 stacked on top of one another) or as (2) individual shear walls but that code restraints may not allow such proportions. Is there something in the code that I am unaware of that would allow this to be engineered.
If not, I fear I need to approach the client to ask them to make the legs of sufficient width so that 3.5:1 aspect ratio is met. Unfortunately this could be an awkward conversation as "another" engineer/firm provided drawings on a previous project of the same dimensions and provided what I believe was something that may not have technically worked. Their design treated the legs as individual walls but provided hold downs only at the boundary element of the entire wall (at say 1' and 14'-8" marks), and provided no detailing for strapping or nail patterns of the headers to the walls.
The project is SDC "D" in WA.
Would seem that an engineered solution is certainly possible as a portal frame (2 stacked on top of one another) or as (2) individual shear walls but that code restraints may not allow such proportions. Is there something in the code that I am unaware of that would allow this to be engineered.
If not, I fear I need to approach the client to ask them to make the legs of sufficient width so that 3.5:1 aspect ratio is met. Unfortunately this could be an awkward conversation as "another" engineer/firm provided drawings on a previous project of the same dimensions and provided what I believe was something that may not have technically worked. Their design treated the legs as individual walls but provided hold downs only at the boundary element of the entire wall (at say 1' and 14'-8" marks), and provided no detailing for strapping or nail patterns of the headers to the walls.
The project is SDC "D" in WA.
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RE: Wood shear wall question
2) Minor point but I'd be inclined to consider the upper tier as two cantilevered, segmented walls rather than a portal frame owing to the limited beam depth available.
3) It sounds as though the previous engineer employed something like the perforated shear wall method.
RE: Wood shear wall question
It is unclear to me what the previous engineer employed. I tend to agree perforated due to the hold down locations except they also extended the low lintel to the boundary of walls similar to a portal. Due to the lack of detailing, it is unclear.
I am going to look into this some more but I believe my approach may be a discussion with the client to explain that we could provide an engineered design that we feel satisfies the spirit of the code but that to we could be at the mercy of what a plans reviewer will want to see or how they view the scenario. This would then let them make the decision to give it a shot or circumvent the potential revision later and just widen the legs now.
RE: Wood shear wall question
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RE: Wood shear wall question
If they went segmented:
1) They may have done it as a two tier thing, for the same reason that you may.
2) To call it two tiered, with any validity, they'd need to run the low beam end to end to serve the function that the top plates normally would.
Just spitballin'...
RE: Wood shear wall question
Personally, I'd put in two strong walls and call it a day (one strong wall calcs, but I'd prefer two for redundancy). But I'm in a market where that wouldn't be an issue.
RE: Wood shear wall question
Expensive, but saves a lot of construction headaches.
Mike McCann, PE, SE (WA, HI)
RE: Wood shear wall question