Wood shear wall barely overloaded in current house design, ideas?
Wood shear wall barely overloaded in current house design, ideas?
(OP)
Hey guys, since I just ran into this issue and am going home for the night, I was wondering if anyone can brainstorm ides here.
I had a wood shear wall with a capacity of 1330 plf in a schematic design before we know all the finishes. The architect decided to casually mention the stone facade, and all the stone pavers on the roof, and the large amount of landscaping soil they want to put over the garage. This increased the seismic weight substantially, but I had enough padding in most of my design that it's working. I will probably need to add a concrete shear wall in the first floor, but the first floor already has several concrete walls so this should be fine.
However, this shear wall in question is at the second floor (there are 3 floors plus a penthouse level). We already have a few moment frames, but I really don't want to add another one! Now this shear wall has an 1800 plf demand. The maximum double-sided shear wall available per the NDS SDPWS has a 1740 plf capacity. So close!
I am personally ok with this.
(1) I am designing as a flexible diaphragm, but in reality the wood diaphragm will provide a good deal of rigidity, taking some load away from this interior shear wall to the exterior shear wall.
(2) The client asked for a high importance factor for their house, so we are designing the whole thing for the extra 50% loads.
But for permit submittal I assume I would have to somehow show that the shear wall will be ok, and I can't do that technically without a very time consuming semi-rigid diaphragm analysis. I could try and add a 3rd layer if the architect OKs an extra thick wall at this location. This may be the easiest option, but was wondering what are the community thoughts on this?
I had a wood shear wall with a capacity of 1330 plf in a schematic design before we know all the finishes. The architect decided to casually mention the stone facade, and all the stone pavers on the roof, and the large amount of landscaping soil they want to put over the garage. This increased the seismic weight substantially, but I had enough padding in most of my design that it's working. I will probably need to add a concrete shear wall in the first floor, but the first floor already has several concrete walls so this should be fine.
However, this shear wall in question is at the second floor (there are 3 floors plus a penthouse level). We already have a few moment frames, but I really don't want to add another one! Now this shear wall has an 1800 plf demand. The maximum double-sided shear wall available per the NDS SDPWS has a 1740 plf capacity. So close!
I am personally ok with this.
(1) I am designing as a flexible diaphragm, but in reality the wood diaphragm will provide a good deal of rigidity, taking some load away from this interior shear wall to the exterior shear wall.
(2) The client asked for a high importance factor for their house, so we are designing the whole thing for the extra 50% loads.
But for permit submittal I assume I would have to somehow show that the shear wall will be ok, and I can't do that technically without a very time consuming semi-rigid diaphragm analysis. I could try and add a 3rd layer if the architect OKs an extra thick wall at this location. This may be the easiest option, but was wondering what are the community thoughts on this?






RE: Wood shear wall barely overloaded in current house design, ideas?
Mike McCann, PE, SE (WA)
RE: Wood shear wall barely overloaded in current house design, ideas?
The Arch. added thickness to the wall, and mass to the EQ design, after the fact, you didn’t. So why should there be an argument about a thicker wall, or when you submit an invoice for the re-do and all the extra work? If you are using double sheets of sheathing, you may want to stagger the edge joints and may need thicker studs and blocking at these new joint locations for the added edge nailing. Those Archs. blow through money like it is going out of style, on really important stuff like gold plated fixtures, etc., and adding a ton of mass up on the roof; then they have the gall or lack of construction knowledge to question that you might need another moment frame for the loads and special conditions they just brought to the table?
RE: Wood shear wall barely overloaded in current house design, ideas?
For the permit submittal, either mention the 3% overstress is acceptable, or mention your other reasons for accepting the overstress.
DaveAtkins
RE: Wood shear wall barely overloaded in current house design, ideas?
For your permit submittal - take away the higher importance factor - which sounds like it was an owner preference and not a code mandated value.
You can add the importance factor into the "for-construction" design and go from there.
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RE: Wood shear wall barely overloaded in current house design, ideas?
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: Wood shear wall barely overloaded in current house design, ideas?
RE: Wood shear wall barely overloaded in current house design, ideas?
Google "Lightweight Soil Planted Roof." It made a difference on a project I worked on years back.
Eric McDonald, PE
McDonald Structural Engineering, PLLC
RE: Wood shear wall barely overloaded in current house design, ideas?
RE: Wood shear wall barely overloaded in current house design, ideas?