Sheathing Requirements
Sheathing Requirements
(OP)
I've got a pre-fab steel building, fully enclosed with a 6" slab foundation. Inside this building my client wants to frame up an interior space and insulate it however he wants to spend as little money as possible and does not want to apply sheathing to the interior walls (12' height) or to the TJI joists of the ceiling. Of course there will be some shearwalls for the seismic requirement, but other than that is there some code that requires full sheathing of the perimeter walls or can he just get away with putting up some fire retardent plastic over top of the insulation (I know doesn't sound like much of a structure to engineer). With the ceiling joists I'm basically of the opinion the whole diaphragm needs sheathing to get the appropriate diaphragm action out of it.
I had previously posted some related questions to this project but now I'm back to the drawing board since the client feels strongly that I've completely over engineered the (interior) structure.
I had previously posted some related questions to this project but now I'm back to the drawing board since the client feels strongly that I've completely over engineered the (interior) structure.
A confused student is a good student.






RE: Sheathing Requirements
Mike McCann, PE, SE (WA)
RE: Sheathing Requirements
A confused student is a good student.
RE: Sheathing Requirements
You mention diaphragm action. If the interior demising walls are not a part of a necessary diaphragm or shear wall consideration, there is no requirement for their materials or finish, so long as they don't change the fire rating of the structure.
If the use of the building requires storage or activity separations that would involve fire ratings for the interior walls, then sheathing and special finishing would be required.
I suppose the bottom line is that if the building is OK structurally without any interior walls and there is no fire rating requirement, your ignorant client can do whatever he pleases with the interior walls.
RE: Sheathing Requirements
On his own time, with his own money, and not under your seal. Just my two cents (which I couldn't give you even if I wanted to, being in Canada).
RE: Sheathing Requirements
I guess I'll try to trim the fat. 24" o/c studs. Only enough OSB on any of the walls to suffice for the seismic lateral loads and ensure the holdown forces do not exceed the capacity of a TitenHD embedded to 4". I do worry about the 12' studs wanting to buckle without any sheathing on one side or the other though at the heaviest loaded bearing walls (TJI ceiling above). Even with that the client has stated he would rather throw some diagonal bracing at it than sheath it with OSB. I'm not sure why the strong aversion to OSB sheathing, with a nail gun and studs at 24" o/c this should literally fly together.
Quality is not the factor here, absolute bare minimum is. Avoid such projects in the future.
A confused student is a good student.
RE: Sheathing Requirements
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: Sheathing Requirements
Mike McCann, PE, SE (WA)
RE: Sheathing Requirements
Gyp sheathing on the ceiling and or 3/8" plywood decking.
Engineering something down to the bare minimum is a challenge in itself. You don't need osb shear walls do you?
When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.
-R. Buckminster Fuller
RE: Sheathing Requirements
RE: Sheathing Requirements
My shearwalls are at the wall lines indicated. I definitely think I can cut back some of the sheathing (segmental shearwall length) on Walls 1,2,3,4 and B while still maintaining acceptable holdown forces (TitenHD into 6" slab on grade), however I still have to use some OSB. The SDPWS-2008 does not give any numbers for using metal straps for shearwalls and gyp. board and lumber are less effective and probably more expensive. Simpson's wall bracing products explicitly state that they are for resisting racking during construction and not a substitute for structural panels:
http://www.strongtie.com/ftp/catalogs/c-c-2015/C-C...
As for the TJI ceiling, the Bldg. dept. will not let me sheath the top since that would allow the occupants to potentially turn the "roof" into a second story. So my next option is to sheath the underside of the TJI ceiling joists with OSB. I've still got to brace the topsides of TJI joists for lateral torsional buckling so I've call out some 1x4 diagonal bracing on the top. However, the question is how do I eliminate some or all of the OSB sheathing on the ceiling. The client just wants insulation, not gypsum or anything else fancy.
I was thinking the diagonal 1x4 bracing will provide some diaphragm action but I have no idea how to calc. that out and prove that it is sufficient given the reactions from the shearwalls.
My seismic data:
SDS = .997
SD1 = .721
Shearwall Loads due to Seismic:
SWLA 8761 lbs
SWLB 8806 lbs
SWL1 2823 lbs
SWL2 5232 lbs
SWL3 4877 lbs
SWL4 2949 lbs
I was also thinking maybe I could just sheath the ceiling around the perimeter in the highest shear areas, but then one would need collectors installed (blocking) at the opening edge so maybe that method just entails more labor.
A confused student is a good student.
RE: Sheathing Requirements
1. Is this a gable roof?
2. What is the issue with just using the perimeter walls for shear walls? Sheath as much as the perimeter wall as you need to.
3. The roof is sheathed, correct? I would say you only need to sheath part of the ceiling near the gable ends (or create some sort of truss). Maybe I'm missing something though.
EIT
www.HowToEngineer.com
RE: Sheathing Requirements
The interior wood frame walls indicated will be used as shearwalls, as I mentioned above they will not need to be entirely sheathed what will govern how much I need to sheath and the length of these shearwalls is the amount of holdown force I can accept given I have no footings under these walls just a prexisting 6" slab with minimal reinforcing. If the shearwalls are too short the holdown forces will be too great and I then would be forced to cut up the slab and install footings underneath which I would like to do at all costs.
A confused student is a good student.
RE: Sheathing Requirements
A confused student is a good student.
RE: Sheathing Requirements
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: Sheathing Requirements
A confused student is a good student.
RE: Sheathing Requirements
My only concern with this method would be that the edges of the sheathing in the north-south direction would need to be blocked and a continuous strap in order to create a chord at these locations. In the other direction the edge of the panel will catch the 2nd TJI in.
A confused student is a good student.
RE: Sheathing Requirements
RE: Sheathing Requirements
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: Sheathing Requirements
A confused student is a good student.
RE: Sheathing Requirements
Seems like a lot of messing around just to save a few hundred bucks on sheathing.
A confused student is a good student.
RE: Sheathing Requirements
The problem is proving the numbers on this might be a bit messy. One could create a model of the whole ceiling arrangement in STAAD or RISA and apply the diaphragm load in both directions. The thing to check would be the forces in the diagonal 1x4 members and then the shear capacity of the nails connecting the bracing to the TJI joists.
Has anyone ever given this a try or am I thinking too far outside of the box?
A confused student is a good student.
RE: Sheathing Requirements
In theory using 1x4 as cross bracing would work. However, there's still a fair chunk of looseness at each crossing connection because they likely wouldn't put in more than 1 or 2 nails. And as the nails are worked the holes will slightly enlarge in the 1x4. But I think it could work.
How is he planning on finishing the walls, he must be putting something either on the inside or out.
And your drywall is expensive, 4x8 1/2" is 8 bucks a sheet at home depot here. OSB is the same.
RE: Sheathing Requirements
You need to work on your client interview process. This is another project of yours where it seems to me you are paying out of your own pocket for the luxury to do the work. I know all about ag clients. Some are good, but others have deep seated issues when it comes to spending money.
RE: Sheathing Requirements
The real problem with the lattice truss concept is that it would be a very weak truss in reality because of the 1 or 2 nail connections as stated by Jayrod12.
A confused student is a good student.
RE: Sheathing Requirements
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: Sheathing Requirements
According to his text the panels around the openings need to comply with the aspect ratio requirements of Table 4.2.4 (4:1 for WSP blocked). I'm exceeding that slightly with an aspect ratio of 4.25 but it is within about 6% so I think it could get a pass.
This method would eliminate approx. 2,400 sqft of ceiling sheething which is equivalent to 75 sheets of OSB, at an average of $10 per sheet we are talking a savings of $750.00.
A confused student is a good student.
RE: Sheathing Requirements
A confused student is a good student.
RE: Sheathing Requirements
With an 8' perimeter this is how it will look. The building dept. is going to think I'm crazy when they see this detail.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Sheathing Requirements
Are they at least sheathing one side? If so, what do you do about compression on the non-sheathed edges when the interior 5 psf goes that way? Do you assume the studs are braced against twist from the sheathing on one side and thus are OK?
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RE: Sheathing Requirements
The client keeps complaining that the structure should be treated like a greenhouse and then I have to explain that there is a few thousand pounds of joists, sheathing, bracing, lights and other potentially unaccounted for loads that are sitting above their heads.
With the shearwalls I've basically decided to cut back on the length while maintaining a holdown force of no more than approximately 2200 lbs. The seismic is governing the design. The idea here is to try and eliminate some of the shearwall sheathing (7/16 osb) but make sure my compression loads at the shearwall chords are still okay to bear on the pre-existing 6" slab. I'm going to use TitenHD anchor bolts for the holdowns and technically my embedment cannot exceed 4" (2" clearance above the soil).
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Sheathing Requirements
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Sheathing Requirements
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Sheathing Requirements
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Sheathing Requirements
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Sheathing Requirements
Most framers that I have talked to say that if you account for the labour costs, sheathing without blocking is cheaper than blocking and cross bracing. Material cost of sheathing may be higher but takes a tenth of the time to install.
RE: Sheathing Requirements
From your wall stud calculation I am getting a 24 psf live and dead loading for the ceiling, is this correct?
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: Sheathing Requirements
TJI DL: 363 plf
TJI LRL: 484 plf
Wall DL: 120 plf
TL: 967 plf
Obviously there is no snow load, however I figured I would treat the ceiling similar to a roof in as much as there would be a construction load (ie. people crawling around on it). The 15 psf dead load is probably a bit conservative but then again the client will be mounting some equipment to the ceiling (distributed) so I feel pretty good about that number.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Sheathing Requirements
blocking at 1/3 points even with sheathing on one side. I also wind to contend with though.
RE: Sheathing Requirements
Will the ext. sheathing count as any sort of bracing at all, I'm assuming not and hence the need for mid-span blocking. I guess I kind of answered my own question there but what constitutes adequate bracing/blocking?
Just from my own experience working with wood and framing a few structures on the farm I know the sideways force caused by LTB is quite small compared with the main axial and bending forces applied to the member.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: Sheathing Requirements
for the entire length. That didn't work so I tried blocking at half then thirds. As far as what constitutes sufficient bracing, I know the steel manual
has a section (look up stability bracing) on it where they actually quantify strength and stiffness requirements but I'm not sure that I have seen
anything like it for timber.
RE: Sheathing Requirements
I say it is highly unlikely that each stud will buckle at the same time, and just as unlikely (or more so) that they'll all buckle the same direction.
RE: Sheathing Requirements
RE: Sheathing Requirements
IT appears as though they say the TJIs could buckle as a unit when only provided with bottom chord bracing, and that they should provide full depth blocking at an intermittent spacing to transfer these loads to the roof diaphragm.
Wall blocking is full depth and as such I would tend to think meets the requirements of transferring the buckling load on the inside of the studs to the exterior diaphragm.
All that being said, medeek's case is unusual where he won't have any diaphragm to resolve the buckling forces into.