Attic floor with trusses in zone D1?

I’ve looked at some drawings of a plywood decked floor system that sits under the trusses on the second story of an ARXX ICF shell in a high snow load/D1 sceismic area. I’m not talking plywood on attic trusses, but an entire structrual floor, decked and blocked every 2′, with J bolt and steel clips attachments every two feet to keep the top of the ICF walls where they should be during a shake.
For you guys in 100 lb snow load areas and D1 sceismic zone, how common is the full blown attic floor with trusses? What design options are there? Trusses designed to take the place of the separate attic floor, perhaps with the plywood decking on the underside of the trusses?
It’s a detail that’s never come up before.
Beer was created so carpenters wouldn’t rule the world.
Replies
Don,
Trying to understand what you are describing.
Sounds as if it a shear element attached to the top of the ICF walls then standard trusses above.
Is that correct?
Snow load shouldn't create the need for such a structural element beneath trusses. IMO
Maybe designed because of wind loads on the building as well as seismic?
Like Dovetail, I have no idea what you're getting at.
It's driving me crazy trying to find the diagram, but I have found a refference to such a beast in the 2003 IRC (R611.9.1) ICF wall to top sill plate (roof) connection for Seismic Deisgn Categories C, D1, and D2.
"... the top of an ICF wall at a gable shall be attached to an attic floor... "
"... attic floor diaphragms shall be constructed of structural swood sheathing panels, attached to wood framing in accordance with... Edge spacing of fasterners in attic floor sheating shall be 4 inches on center for Seismic Design Category D1..."
Beer was created so carpenters wouldn't rule the world.
I'm having a hard time figuring out what the problem is or just exactly what you're after. But maybe it's because I've only dealt with wind design, and not seismic. I'd help you if I could...
The qualities that most attract a woman to a man are usually the same ones she can't stand years later.
Boss,
Reading Don's copied stuff I see that the point of the diaphragm is to stiffen the GABLE walls against seismic activity. It doesn't mention the bearing walls at all. Roof sheathing should act as the diaphragm for the bearing walls as ,long as it is all well tied together if I understand the engineering at all correctly. The last winery I did we had to do a whole lot of blocking and bracing and use a bunch of Simpson stuff to the same effect if I correctly understood the engineer at the time.
They can't get your Goat if you don't tell them where it is hidden.
Well, I believe ya. This just isn't something I have an expertise with.
How can a president not be an actor?" [Ronald Reagan, when asked "How could an actor become president?"]
An engineer described a house in an earthquake as being like a pencil on end, it wiggles back and forth, but not a lot of stress. Now add a significant snow load and it's like having a lemon stuck to the end of the pencil and the whole structure needs to be able to handle the extra stresses. I think he could have come up with a better analogy, but it make sense that more weight up top effects what happens throughout the structure.
Now I'm not suggesting that the "attic floor" under a set of trusses is the standard way to go, but it's an option used by some. I can't imagine the trusses can't be engineered and cross blocked, perhaps sheathed on the underside with ply and accomplish the same thing.
Beer was created so carpenters wouldn't rule the world.
I would think the same. the trusses should be able to be designed to allow for that to happen as long as the connection at the gable end was sufficient.
They can't get your Goat if you don't tell them where it is hidden.
Trusses can be designed for just about any situation. We can input something like 40 load cases for each truss. and produce a mountain of paperwork to support it. Most of the time all these different load cases don't really change the truss. It's just done to satisfy architects an engineers.
Work your fingers to the bone, waddaya get?
Bony fingers.........
Don't know if this works anywhere else, but in Alaska if you engineer for the winds, the seismic is usually taken care of.
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