Suggested reading material for my structural engineer?
Matteus_Olmedo
| Posted in Project Management on
I just received my preliminary structural drawings and the engineer obviously ignored my request for advanced framing to be used. Granted I’m in D2 seismic zone but I know less wood could be used. Anyone know of any good articles by SEs for SEs on utilizing advanced framing techniques in the structural calcs? Here is one I came across, for example…
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Replies
Matteus,
Are you using exterior insulation, or other wall assemblies that are more efficient than the standard one commonly specified? If so that's where the lion's share of the gains are made, not in the advanced framing - and to me that's where I'd concentrate may efforts, rather than compromise on structural integrity in a high seismic zone.
An old GBA post from 2011 with no responses: https://www.greenbuildingadvisor.com/question/spray-foam-and-shear-walls. The post mentions gluing of shear wall panels to studs with or without mechanical fasteners as being a possible code violation. Wondering if use of adhesive on exterior insulation would have any change on desirable behavior of shear walls?
The 2011 poster's ultimate question was:
"Curious how spray foam would affect stiffness, since it is very adhesive and would seem to also stiffen the wall considerably, and if this could result in the same issues as with gluing the sheathing to the studs? Any ideas?"
Shear handling during construction is good too if in seismic/wind zones, I saw an architect's framed custom 2 story home become a 1 story home after a not so strong storm.
PBP1,
I have only heard of problems with adhesive on shear-walls when it is used in-between the shear panels and the framing underneath. The panels need to be stiff, but also be able to give a small amount under the shear forces of seismic events so the sheathing isn't damaged. I'd imagine exterior foam would detach at the surface before it caused problems for the plywood underneath.
Thanks, sounds reasonable. Lived in a concrete/cinderblock three story building that got hit by an earthquake at 3 AM about 20 years ago to the date, w/little ability to handle shear, there were cracks in all the walls and the grinding noise was hair-raising.
From a quick search: "Thermal and Shear Wall Performance of Building Assemblies with Insulated Frames" https://web.ornl.gov/sci/buildings/conf-archive/1998%20B7%20papers/062_Charlson.pdf Appears to be for mechanical attachment of extruded foam insulation between shear panel and structural frame.
There is some research showing that in a seismic event the walls perform slightly better with a slip-sheet of thin foam in-between the plywood and framing. But that's at the expense of a lot more lateral movement. You give up some stiffness for better resistance against total collapse. I guess that begs the question as to how much damage are you willing to accept before you wished your house had just gone ahead and collapsed?
Malcolm, thank you for the reply. I am planning on using exterior foam but it is still frustrating to receive a design with 4x6 corners instead of two studs with drywall clips like I requested. At the end of the day you are using more material to accomplish the same result and good engineering should be much more efficient.
Matteus,
I agree there is some redundancy in standard platform framing, but consider that one of its positive attributes. For the small amount of additional lumber you get a more robust structure able to adapt to any damage or unforeseen forces that may occur in the future.
That general proposition aside - yeah, I'd be pretty annoyed to find details like 4"x6" corners on an engineer's drawings. It does sound like they haven't taken your concern with efficiency at all seriously.
From a theoretical standpoint advanced framing makes a lot of sense. Less material, higher assembly R values. Win/Win. As a engineer, I really like the concept.
In reality it doesn't work that way. I've tried most of the details and only a couple are really worth the headache.
-24" OC framing
-2 stud corners with clips (or 2 stud with 2x4 backer for drywall)
-raising structural headers into the rim joists
-2x6 backer for interior wall intersections (much simpler than ladder frame and makes air barrier transition easier)
None of these are require much, all are part of most prescriptive code packages. Even the raised header is probably something they have already done for any large opening as it is the typical way to support floor to ceiling windows.
These few items gives you most of the gain from advanced framing and requires no learning curve from the framing crew.
Akos, thank you for the reply. I regularly use these methods (as well as single top plate, header hangers, and continuous drywall), but this is my first time straying from a prescriptive build and I unfortunately failed to adequately communicate this when hiring an engineer. How can I best influence him to agree to utilize these prescriptive methods in his drawings? Also, do you see the FTAO or PSD methods as being favorable to reduce framing? My engineer is using SSD method and it is frustrating as a builder and designer because of it's inefficiency in failing to account for shear nailing above and below windows.
I'm not in a land of seismic or high wind, so I can't comment much on the best approach.
One thing you can ask is if the engineer cares about the detail on the drawing or was included as part of boiler plate drafting. If it is not needed, it can be removed from the drawing and you can use prescriptive details. I've run into this before where the structural engineer speced $2500 worth of Hilti hardware because of copy and paste when in reality a couple feet of 1/2" threaded rod was all that was needed.
Akos, good to know. Thank you
Hi,
Do the 4x6's in the corners have hold downs? If so they are the ends of a shearwall. The 4x6 are typically used if the nailing is 4"0c or less or for the compression load of the shearwall chords.
Yeah they all have either ST6236 or MST48s. It is my understanding that PSD or FTAO shear methods can reduce the end wall requirements