TJI FLOOR JOISTS 8

[Standard American]

Truss Joist TJIs come in a wide variety of chord widths. Is it really practical to use a TJI with a chord width less than 3 1/2" for a floor joist? Less than 3 1/2" chords sound like it will be an issue when decking and if you use the smallest TJI with 1 3/4" chord your floor deck really doesn't have a whole lot of bearing. Anyone know what the cost difference is from TJI 110 to TJI 560?

 

[IceNine]

It's got more bearing than a 2x12...

 

[Standard American]

Solid response

 

[jayrod12]

Yeah I'm not usually concerned about that. I have my own other reservations regarding TJIs, but that may not be the intent of this thread.

 

[phamENG]

but that may not be the intent of this thread.

Too bad. Inquiring minds want to know...

 

[dik]

Only concern about TJIs I have is their action in a fire. They lose strength very quickly and can be a hazard to first responders.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[phamENG]

dik - fortunately, manufacturers started addressing this with some fairly significant R&D 15-20 years ago when those reports first starting coming out and fire marshals were insisting building officials deny permits if the plans specified them. The result is a set of adhesives (both internal to the panels used in the webs and between the flanges and the webs) that have substantially improved resistance to heat. It's been a while since I looked at the test reports, but as I recall the TJI as a whole help up roughly as well as standard dimensional lumber. So yeah, not great, but also not unexpectedly terrible anymore, either.

 

[jayrod12]

Too bad. Inquiring minds want to know...

Fair, so beyond dik's concerns with you've already responded to (I still find the OSB part of the joist to not stand up in a fire compared to solid wood joists), my main concern is diaphragm capacity and how they have found that the capacity of a diaphragm is lower when using TJIs but they don't advertise that reduction. I came across the attached just doing my own digging through their technical letters.

 

[phamENG]

Thanks, jayrod. That's interesting. I guess it has to do with nail penetration in the top flange...can't go any deeper than 1.5". I'll have to look into the US literature and see what they say for applications with NDS.

 

[XR250]

Ask any remodeling contractor if they like TJI's (answer - NO)
They also seem to creep under sustained loads in my field experience (like under kitchen islands)
They also dislike high humidity which adds to the creep.
They also fall apart way quicker than dimensional lumber when exposed to water from, say, a slow plumbing leak.
They also buckle if not blocked under point loads.
They also dig into dropped girders under long 2-span conditions.

Did I tell you I don't like TJI's?

 

[kissymoose]

They also dig into dropped girders under long 2-span conditions

what is this?

 

[XR250]

The bearing pressure due to the small contact area tends to crush the girder and/or the bottom flange of the I-joist. Not a big issue until you have blocking on the top of the girder that does not crush.
Causes a nice hump in the floor.

 

[jayrod12]

I believe he's talking about the localized bearing issues below long two-span joists. Often the high loads coming in on continuous joists cause noticeable crushing of the beam material. Theoretically it could happen with really long span single span joists, but it seems to be less of an issue in those instances.

 

[Aesur]

@Standard American - I assume you are using Forte being that it's TJI's - if you are it gives you a cost index that tells you roughly the cost difference.. I just did a quick example calc and see that TJI 110 cost index is 0.69 and 560 is 1.5, so over 200% more expensive...

 

[dik]

They have a lot of surface area that can 'cook'.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[RontheRedneck]

We sell I-joists, but not the Truss Joist brand.

At the risk of telling many of you things you already know, I hope you don't mind if I list a few things that not everyone reading the thread will know.

Truss Joist brand (TJI) is a brand of I-joists, just like Kleenex is a brand of tissue.
In my experience, Truss Joist is an arrogant company that's difficult to deal with. I try to avoid working with them when possible.

The most common flange width sold around here is 2 1/4" or 2 5/16". They're less than half the cost of the ones with a 3.5" wide (4x2) flange. And much more readily available.

I-joists more than tripled in price during the pandemic, and were sometimes hard to get. Now pricng is softening up a bit.

I have never known the narrow flange widths to be an issue. As IceNine said, they're all wider than 2X lumber.

Someone mentioned kitchen islands.

Floor members of any kind can deflect more than adjacent members under a kitchen island. A lot of time there is nothing sitting in the area on both sides of the island. The deflection under the island may be within the allowable deflection. But the fact that they're setting next to something that's not deflecting nearly as much makes it look bad.

At the place I work at we automatically double up I-joists or floor trusses under kitchen islands for that reason. It doesn't cost much up front, and can save a lot of trouble down the road.

One thing I don't like about the various I-joist suppliers is that they send literature to architects and engineers with every line of I-joists that they can manufacture. But the regional warehouses may not carry but one or 2 product lines, even though they literature shows maybe 4 to 6. So we often get plans with things specified that are not readily available.


I often see the highest line of 11 7/8" I-joist called out. Seems like everyone wants to keep the depth down, and the 11 7/8" depth is what they're after.

But to get that depth, they often go way over the length/depth ratio I like to see. (18-to-1 is my personal limit based on experience. i.e. 18' of span per foot of depth)

Sometimes a series of 14" I-joists is more readily available and less expensive than the super HD wide flange 11 7/8" I-joists. But getting someone to agree to the added depth is often a lesson in futility.


Sorry if I rambled a bit. But I deal with these issues all the time.

 

[dik]

Appreciated...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[1.392DL]

We spec TJI floor joists all the time. They're lighter and easier to get larger MEP openings thru. You can get longer sticks than 20ft. Most importantly, they are true and flat which makes for a good clean install. One downside is needing web stiffeners for higher loaded joists which plays into the decision to use a stronger joists.