Weyerhauser TJI Deflection 3

[TORCHMAN]

People in my area love using TJIs. I like spec'ing it as they have a great specifier's guide. But I realize that I am unsure about some aspects of spec'ing this product and I cannot find a good Weyerhauser contact. Does anyone here know how to get in contact with their technical team?

Below are my questions:
1) Do you guys stick to the specifier's guide or do you check deflections using their formula? I find that I can stretch the joists longer than their specifier's guide using their formula (below) while still keeping it well under the L/360 deflection. For instance, their 11-7/8" s47 TJIs @12" o.c., I can get a L/420 (19mm) with a 7.9 span (26') - 1.9kPa Live Load, 0.5kpa Dead Load, simple span. Their table only allows a 21'-10" span. That is a big difference.
I also checked for moment and shear resistances, 15.7kNm and 13.52, respectively and they are much higher than my factored moment and shear, 8.13kNm and 4.12kN, respectively

Is this issue vibration?

2) As mentioned, I use their formula for calculating deflection, but they have different allowable spans based on the different subfloors installed. This is not accounted for in their calculation. Why not? I spec 3/4" ply on longer spans that match their specifier's table, but it would be nice to derive it through an empirical formula.

Your input is appreciated!

Happy Thanksgiving!

 

[Goatenstein]

All the guides I'm finding say that the allowable spans are vibration controlled.

 

[jayrod12]

Deflinitely a vibration thing. I can't see how you can get a roughly 12" deep I-joist to work in locations where we are consistently running 18-24" deep open web wood trusses. I'd bet the vibration calculation is through the roof.

Honestly I can't imagine a l/d of 26 working for wood. I'm usually in the range of 12 to 16.

They do however have a free web app for checking everything, look up ForteWEB. They even do the vibration analysis.

 

[ChorasDen]

Span tables found within the design guide are vibration controlled. Not sure how to call the Canadian engineers, but if you want to discuss with them via email, you can reach out via techsupport@wy.com. Alternatively, the phone number for the U.S. based engineers is 888.453.8358.

 

[Canuck65]

Torchman,

I have never had a problem in Ontario picking up the phone can calling Weyerhaeuser's support number. I have been able to speak with some knowledgeable tech reps.

We (and anyone other engineer I know) only look at preliminary sizing. As the structural engineer of record for the project we provide the loading criteria and quite often we also provide deflection criteria. Depending on the project our deflection criteria often is more restrictive than required by code. Then the lumber supplier provides shop drawings for the floor design that has been generated by Weyerhaeuser's full blown software.

Vibration limits the span of both TJI's and regular dimensional lumber. Take a look at the Part 9 OBC tables for floor joist spans and if you look carefully, there are certain joist configurations that can span further if they have a concrete topping than without. Counterintuitive for sure, but the extra SDL dampens the vibrations.

If you 'calculate' and allow spans that exceed the Weyerhaeuser tables, you will have a floor that won't collapse but will perform very poorly.

Like the additional span tables for glued and nailed floor systems, many of the span tables are generated based on testing, in conjunction with calculations. You cannot recreate some of these tables with only calculations.

 

[lexpatrie]

Isn't ForteWeb.com Weyerhaeuser?

It's pretty basic stuff but it has its uses and I think it will do vibration and stress and deflection. Some of the output isn't my favorite (it gives a maximum unbraced length versus giving a compressive allowable stress, and it can be a little tough to replicate their work but it seems pretty rigorous for what it does). It also does dimensional lumber which is pretty nice. You can't always design stuff full-on in ForteWeb (due to limitations) but sometimes you can establish that you need "at least" something using their software, because you can't model it quite right in ForteWeb.

Regards,
Brian

(Yeah, scrolling up I realize Jayrod12 already mentioned ForteWeb).

Also as a side note, in fire rated construction or UL assemblies, you may need specific minimum depths or spacing for the TJIs. Like a lot of corridor assemblies I see are for 2x10s minimum, a TJI isn't a 2x10.

As another side note, there's been testing on I-joists as to diaphragm strength (because they are what, 1 3/8" versus 1 1/2" for dimensional?).

https://www.structuremag.org/?p=4692

looks right.

 

[XR250]

I generally use their tables but if I was doing the math, I would not be going any less than L/600. In my experience, TJI's and floor trusses creep a lot more then they should - especially under sustained loading - such as kitchen islands.

 

[Eng16080]

I went to an I-Joist seminar a few years ago. I forget if the presenters were from Weyerhaeuser or Boise Cascade, but they referred us to their design span tables and told us never to use the L/360 criteria. I suspect they realized vibration was an issue with the more slender sections used with the L/360 criteria.

Perhaps this isn't relevant to the thread, but it's worth noting that I-Joists are required to be fire protected. This is important where I-Joists would typically be exposed in unfinished basement areas. Refer to IRC Section R302.13. Most engineers/architects that I've mentioned this requirement to had no idea. Apparently, unprotected I-Joist floors perform very poorly in a fire. I've heard (through the internet) that certain fire departments will not enter the first floor of such a building if it's know that the floor is framed with I-Joists.

 

[lexpatrie]

Fire Engineering (the web site/magazine) has some coverage of that issue, as a side note. The IRC requirement is fairly new, perhaps 2012, maybe 2015.

2009 - *images no longer load*

https://www.fireengineering.com/fire-prevention-protection/construction-concerns-5/#gref

 

[TORCHMAN]

Wow, thanks everyone for all your input! What you say makes a lot of sense and also I never knew about the fire rating issue.

I never used ForteWEB but I will be sure to check it out!

This community is amazing and I am glad I joined the forum.

 

[RontheRedneck]

Pardon me if I'm very opinionated on this subject. But I design a hell of a lot of floors, and do it every day.

My rule of thumb is L/D is 18-to-1. So I push hard to not have 11 7/8" I-joists span more than 18'.

I don't care what the span charts say. People come in wanting to put them 12" OC and span 20' or more. I end up fighting this battle a lot.


If you're specifying them, I'd strongly suggest finding out what's actually available locally. We occasionally get plans where they spec an I-joist with a very wide span so they can get them to work at the depth they want. When we call out suppliers, they sometimes tell us that we'd have to order them in truckload quantities, they have long lead times, and they're very expensive.

In most of these cases if they're willing to just go up one depth (like from 11 7/8" to 14") locally stocked I-joists will work fine. And the deeper stock ones are less expensive.


I saw that someone mentioned kitchen islands. We virtually always double up Both I-joists and WW floor trusses under them. The exception would be if it's centered over a beam, or something like that.

I've been following the 18/1 rule of thumb for about 25 years. I've never had an unhappy customer who followed my suggestions. Which is why I'm opinionated.

 

[lexpatrie]

That reminds me: Frank is the guy. I was pretty worried during that VT active shooter.

https://www.woodworks.org/wp-conten...oors_to_mitigate_floor_vibration_problems.pdf

I suspect this is more oriented to trusses and dimensional framing, but it's good background if nothing else.

Regards,
Brian

 

[RontheRedneck]

The research that Frank Woeste did is what convinced me to be more conservative in floor design.

 

[dylansdad]

I took a class back in the day at VT under Mr. Woeste. Great and knowledgeable guy.