TJI w/ web stiffeners flexural strength 1

[cbinder]

A contractor approached me about a fix for a house I designed. Specifically, the stairs don't meet minimum head heights. What he wants to do is stiffen the web on both sides with 1" plywood, provide a small stud pack on either end of the span and then cut out 5 inches of the joists depth. Obviously, this would:
1) remove the bottom tension chord from the TJI and a few inches of the web.
2) turn that 4' span into a composite beam

The load pathing of the proposed fix all makes sense and will work, my only question is how would I go about determining the allowable bending stress of that composite. Total thickness and depth of the remaining wood would be 2 3/8"x6". Our wood species of choice is Douglas Fir Larch.

Thank you in advance for any advice

 

[KootK]

I'd be inclined to discount the TJI remant entirely and evaluate the member assuming that the two 1" pieces of plywood are all that there was s to it. You know, if that works.

 

[cbinder]

That was one option I was thinking, but I don't know where I can find the allowable bending stress of plywood.

 

[cbinder]

and as I post that, I find this

https://www.pfsteco.com/techtips/pdf/tt_plywooddesigncapacities

 

[cbinder]

also, found this

http://www.ecodes.biz/ecodes_support/free_resources/Standards/APA/PDFs/H815_2008.pdf

Section 1.5

 

[phamENG]

As one who recently went down the rabbit hole of TJI reinforcing, DON'T DO IT. When you start messing with these things they don't come back very easily. I didn't look into flange damage all that closely (I was concerned with a damaged web), but from the little I did look at that it was typically worse than web damage.

Here's a link to the thread I had on the topic. Near the end I post a link to a PhD dissertation that looks at both web and flange cuts.

I would strongly suggest adding the studs, cutting the TJI back to bearing on each side (along with necessary bearing details, etc.) and add a new member that is the correct depth - be it dimension lumber, LSL, LVL, etc.