How to analyze plywood over SIPS panel
How to analyze plywood over SIPS panel
(OP)
I have to determine the capacity of a floor that consists of a new layer of 3/4" T&G over an old SIPS panel. The building is being converted from residential to office space and the extra floor live load has to be addressed. The remodel is already done, building red-tagged, and I am now justifying the as-built.
My first thought was to find the properties of the new total section (convert the moment of inertia, etc), but this neglects the shear deflection of the core and may be unconservative (this may be why SIPS uses tested values). I also considered looking at the individual rated spans and just superimposing them, but this neglects that the bottom face of the SIPS panel is taking all the compression from bending.
Actually, my very first plan was to tell the contractor to add some beams, but he'd like to know it doesn't actually work, first. Any thoughts?
My first thought was to find the properties of the new total section (convert the moment of inertia, etc), but this neglects the shear deflection of the core and may be unconservative (this may be why SIPS uses tested values). I also considered looking at the individual rated spans and just superimposing them, but this neglects that the bottom face of the SIPS panel is taking all the compression from bending.
Actually, my very first plan was to tell the contractor to add some beams, but he'd like to know it doesn't actually work, first. Any thoughts?






RE: How to analyze plywood over SIPS panel
RE: How to analyze plywood over SIPS panel
RE: How to analyze plywood over SIPS panel
The live load is going from 30 psf to 50 psf.
RE: How to analyze plywood over SIPS panel
RE: How to analyze plywood over SIPS panel
However, since both pieces are rated products rather than calculated sections, that transformed section calculation uses alot of guesses and completely neglects the shear deflection of the foam core.
RE: How to analyze plywood over SIPS panel
I would draw a section of the spline+ 7/16 osb on each side of the foam + 3/4 new plywood on top of it (4 ft wide). Just assume everything is DF #2. If you go this direction, I have a feeling the inspector would want to see the shear flow calc on the new plywood.
RE: How to analyze plywood over SIPS panel
Dik
RE: How to analyze plywood over SIPS panel
I only have to justify it to myself - not much building department second guessing in this area. In any case the shear flow between new and old won't be a problem, it's well attached. But because I don't have a feel for SIPS panels, I'm worried about overstressing the bottom plywood and worried about excessive deflection I can't predict.
RE: How to analyze plywood over SIPS panel
RE: How to analyze plywood over SIPS panel
Another option is to adjudicate the floor loading to a lower occupancy. Office occupancy at 100 sf per person may be reudced to say, 200 sf per person. The building would have to be posted for the reduced occupancy but seldom do the number of occupants reach what Chapter 10 Means of Egress allows. Just an idea if you are short a couple of psf in your analysis.
Don Phillips
http://worthingtonengineering.com