1979 Wood I-Joist Capacity 2

[JrStructuralEng]

Hi,
I was inspecting a 1979 condo unit (in Canada) that has original Wood I-Joists with no clear identification on the drawings or on the product.

Does anyone know how I can detemine the capacity of such a product? Currently the joists appear to be under-designed based on deflection and we are anticipating having to cut down the span. I was hoping to find span tables on the joist but I am worried this will come back to first principles. Any advise on either way. I don't even know where to start for designing an I-Joist from first principles.

The joist appears to be douglas fir top and bottom chord. 1.5" deep by 1.75" wide. The web is 3/8" thick fir plywood that is embedded in the fir chords 5/8". The joist is a total of 11-7/8" deep.

There was only one stamp on a single joist (on the plywood) that indicated:
B0131
COFI Exterior Canada
CSA 0121-1X
DFP

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Any Help Would Be AWSOME!! Thanks!

 

[Lion06]

If you know the species this should be a fairly straightforward calculation. Assume a grade (pick a low grade first to be conservative) and do your checks based on those values in NDS.
The chords take the moment, the plywood takes the shear.
Check deflection using the E of the chords. I would probably neglect the contribution of the plywood web in the calculation of I.

 

[unclesyd]

You might want to contact several of these links for information on your joist.

http://i-joist.org/links.asp

 

[unclesyd]

The reason I posted the above links is that I've got 2 B&C books dated 1975 and neither even mention I-Joists. I also have part of a magazine article (1980) that states that there are no standards yet for I-Joists and one has to depend on the manufacturer for details. This article also states that there are only 4 types and if you want anything else it has to be custom.

 

[msquared48]

You might want to contact Truss Joist MacMillan Corporation and see if they have any leads for you. With those dimensions, they sound like standard 11.875" TJI's, just a different era. (1-800-628-3997) or

http://www.trusjoist.com.

Mike McCann
MMC Engineering

 

[JrStructuralEng]

StructuralEIT, I do not have much experience with wood design (nevermind I-joists). I am assuming there are some reduction factors that need to be used. When calculating the moment would you neglect the web altogether to simplify the calculation? If I want a more accurate capacity wouldn't I need to take into account shear flow between the two members?

Can anyone post a simple example for I-joist design? or point me in the right direction?

 

[JrStructuralEng]

Mike, thanks for post, I will try them on MOnday. If anyone else has any info in meantime that would be good

 

[Lion06]

Yes, there are factors that need to be considered in the determination of your allowable stresses. I would neglect the web when calc'ing the allowable moment.
The shear flow between the chords and the plywood web won't affect the capacity of the member in bending. The connection needs to be able to take the shear flow but it doesn't affect the moment capacity (unless it can't take the shear flow, but then you don't have a composite section anymore and your plywood web is doing a lot of work in bending).

 

[unclesyd]

You might be able to glean some information for the literature at APA site.

http://www.apawood.org/level_c.cfm?content=pub_joi_libmain

Here is Jager Engineered Wood Products a company that has apparently been in the business since 1980. They might be able to give you some information about the early I-joists. There is a lot of info at this site.
I might add their construction details are outstanding.

http://www.jagerewp.com/data.aspx?path=JSI Joists

 

[JrStructuralEng]

Does anyone know when Canada implemented vibration controls for engineered wood products. Based on my current research that appears to be the only case where these joists are not meeting current code requirements.