Hi guys,
I am building a new home soon and had a question on TJI span.
Some details; the widest portion of the basement foundation is 35’6″. There will be a 2X6 bearing wall (instead of a beam) that splits the span into two sections – one that will span 16′ and the other will span 19′.
My question is that the lumberyards/truss companies have all spec’d 11 7/8 inch TJI’s 16 inches on center for the floor system, will this be adequate?
I do not want a bouncy floor or one with a lot of vibration. The portion with the larger 19′ span will be under the master bedroom, master bath, and hall bath (a lot of weight and some tile).
Would it be a better idea to go with 14 inch TJI’s to be on the safe side? I would rather spend the extra and have a solid floor.
Need some expertise.
Thanks
Jim
Replies
I saw a buider did 12 oc cross whole two car garage that is over 20', probably 24'. I went to the master bed above the garage and surprised to see the floor being very sturdy. I also think too thick of joists doesn't look good.
From a table found here http://www.ilevel.com/literature/TJ-4000.pdf, the TJI 230 series joist at 11.875 depth will handle spans up to 19'2" and deliver floor performance of L/480 at a loading of 40 psf live / 20 psf dead.
As Miles Davis said to a reporter when asked whether he smoked dope, "Wuz wrong wid dat?"
What are you hiding in your grand piano that makes it so heavy?
Gene,
Do you happen to have access to the "TJ Pro Ratings" as described on page six of the link you posted?
I recently spec'd some TJIs using only the manufacturer deflection tables, but apparently that table led to a design that did not typically result in "customer satisfaction."
I'm assuming the "TJ Pro Ratings" have something to do with floor vibration as BossHog has mentioned numerous times.
One thing to consider in this particular case is that the floorjoist design is not for a simple span, but for one continuous across a single central bearing, with the spans being unequal.
Equal or no, a beam sized for a simple span condition (in this case the larger side, or 19 feet) but that will actually be done as a longlength continuous, results in a selection of a larger section than what might otherwise be chosen.
I speak of "beam" in the structural engineer's sense (I can't help it.) Any floor joist is analyzed as a beam, one whose loading is figured from the tributary area (sorry for the engineer-speak) of floor load being carried, which is of course dependent on joist spacing.
Thus, the TJI230 11.875 will likely deliver higher "performance" (i.e. less deflection, less vibration) than otherwise, the design being for a continuous span.
A word about span. Sizing for a floor frame, the building width being 16 plus 19 feet, total 35 feet, but with end bearings of, say, 2x8s sitting atop ICF walls, and the partition bearing being a 2x6 wall centered on the 19-foot line, the two between-bearing spans turn out to be 15'2" and 18'2". One wants to be sure to use these, and not the "nominal" numbers of 16 and 19. Loading correlate to the square of span, and inches count.
Gene,
The "engineer-speak" is fine -- using the right vocabulary aids in the discussion. And I have an ME degree myself, so I remember basic beam loading scenarios. The more complex loading arrangements are things I've managed to forget since college. ;)
in this particular case is that the floorjoist design is not for a simple span, but for one continuous across a single central bearing, with the spans being unequal.
Where did the OP say he was going to be using a continuous beam?
Anyway, I think you forgot to answer my question about the "TJ Pro Ratings" as described on page six of the link you posted -- do you have access to that, or have you used that database before?
Re continuous, since TrusJoist makes the joists in long lengths, I presumed his vendor was quoting full length stock. Depending on your dealer's ability to handle things, joists are available at lengths close to 45 feet.
Yes, the I-Level download I cited shows the ProRatings stuff on a later page. As you know, tables aren't given, or at least they are not seen in my download. It looks as if the TrusJoist wholesalers have some company-provided software that permits some more detailed analysis and sizing.
"Depending on your dealer's ability to handle things, joists are available at lengths close to 45 feet. "
Around here (where the OP is located) everyone stocks 48' I-joists.
I've never known of anyone to stock longer ones than that. Eventually they get too heavy and too flimsy to handle.
Better to remain silent and be thought a fool than to speak out and remove all doubt.
"Where did the OP say he was going to be using a continuous beam?"
With I-joists, I think that's generally assumed. One of the benifits of I-joists is that you can use one long piece instead of lapping them over a beam.
I don't think I've ever done lapped I-joists where a one piece I-joist would work.
In the city, you can only see from horizon the horizon what man has made.
In the country, you can see from horizon to horizon what God has made.
If you want is solid, put in 12" high steel "I" beams.
Unless you have a standard there is no way you will be happy.
I find a l/360 deflection at 40# live load suitable.
Thnaks guys for the helpfull answers. Sounds like the 11 7/8 TJI's should be fine.
GHR - I was looking for some real feedback not a smart a** answer.
Jim
Ignore GHR - He's never once posted anything useful on BT. He just likes listening to himself. Have you read the thread I did on floor vibration? You can find it here:http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=21010.1Persnally, I don't like going over 18' with 11 7/8" I-joists. But the brand and series we sell is rated for 19' 8" at L/480, and many people go right up to that. We haven't had too many problems with vibration call backs.And chance you can move the wall, even a few inches? Any amount that you can reduce the span will help. Is the 19' you mention the clear span between walls, or is that maybe from the outside of the foundation to the center of the wall?I would not recommend going to 14" I-joists if you can avoid it. The 11 7/8" I-joists are a hot commodity around here, and are fairly inexpensive. But 14" I-joists are a special order, and there's a significant upcharge. Best of luck with the house...
Happiness, n.: An agreeable sensation arising from contemplating the misery of another.
The 19' is the clear span between the walls. From outside of the foundation to the center of the 2X6 wall is 19' 10".
As far as the spans, I have read span tables that are broken down to simple span and multiple span - I think Gene was refering to these.
Thanks Again
Jim
I've never seen anything that suffested that mulitple spans made any difference when it comes to vibration. It certainly affects strength. But vibration is a different issue altogether.
I have a great new motivation tecnique, it is donuts, and the possibility of more donuts. [Homer Simpson]
You took your plans with all the dimensions and loadings to a professional with software and you were uncertain about the professional's design.Now, you come here ready to take advice from a bunch of idiots who know nothing about your needs or your design.---As I said without a standard you will be unhappy.
Now, you come here ready to take advice from a bunch of idiots who know nothing about your needs or your design.
Don't be so hard on yourself, GHR. Not everyone here thinks you're an idiot.
I can't decide if you're a dumbasz or a just a dick...?
LOL.....View Image
reducing the spacing of joists always seems to not give you a lot in return. It seems like you gain little in stregth or stiffnes for the amount of lumber added. Always struck me a sort of odd.
look in the span charts
Thank you all for your opinions!
Reading from the Floor Span Table, a TJI-560 Joist 16" depth, 16" oc can span 29'-8". So if I have a 28x40 foundation, there's no lally posts are needed. This will sure make a large, nice basement. But I haven't seen any house without lally columns. Is this a good construction w/o lally posts? Thanks.
The 16" TJI's will be fine, but expensive. Might be worth it for the design freedom you gain in the basement. Will it be a shop, living space, or just a basement?BillP.S. You might be better off with floor trusses at 28' span. Ask Boss Hog.
Edited 8/24/2007 2:22 am by BillBrennen
It will be a living space.
Thank you all for your responses.
My 95-year-old aunt has a roughly 20-year-old "garden apartment" condo with floors that squeek big time. I investigated to figure out why and found that the joists span the width of the home, with no center support (crawl below). The squeeking comes from the floor moving up and down relative to the wall running down the center. I suspect it's then nails in the bottom plate that are squeeking as they slide in and out of the floor. The floor motion is imperceptable, but it squeeks big time.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Anything that suggests using at that layout would be for live load on the floor system only. Add walls and roof load transmitting and you come up with serious problems.
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A 16" I-joist spanning 29'-8" would have TERRIBLE performance, IMHO.I ran it through my spreadsheet, and it came up with a score of 10 for the "F" value. Ideally, the "F" value should be 15 or more.
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Out of cuiroisty, Boss. What depth of truss woud be needed to make that span?
If you were talking wood webbed trusses, I'd go 22" or 24" deep. That's a lot of depth. But you can get all your mechanicals in there that way - Even HVAC. And having no beams or posts is great.
Life is what happens to you when you're making other plans. [John Lennon]
I ran it through my spreadsheet, and it came up with a score of 10 for the "F" value. Ideally, the "F" value should be 15 or more.
What's the "F" value, Boss? Frequency?
Edited 8/24/2007 3:54 pm ET by Ragnar17
A value of 15 or more for the "F" value should be acceptable to most anyone. A value between 12 and 15 is marginal.Anything below 12 is generally unacceptable.
Thanks for the response, Boss. I guess my question should have been: how is the "F" parameter calculated, and what are its units?
Since you said you got the number out of your spreadsheet, I'm assuming it's something more quantifiable than TJI's "customer satisfaction index" (or whatever it is they call it).
The "F" value is calculated in the spreadsheet. And I based the spreadsheet on info I got from some research at a university. Unfortunately I'm at my Brother's house now, so I don't have any of that stuff available to me at the moment. (That's also why I'm not adding tag lines)If you don't mind replying to this message so I see it on Monday, I'll try to dig up some more info then.
Thanks, I'll try to remember to do that.
Boss,
You have my pure and total interest with your spreadsheet knowledge.
I'm building a two story cabin that 16'x32'. Lumber costs are only 15%-25% of retail, so I've aquired a lot of lumber. For the ceiling joists that support the second floor I made them using 16' long 2x8's with a 2x4 glued, ringshank nailed and screwed together, making an I-beam. They actually measure 10-1/4" by 16', and are placed on 16" centers.
Because of the heavy bouts with a very wet spring and summer, after I had mounted them across the 16' span, I discovered I had some extra time and many long 2x4's left over. So, applying subfloor adhesive, I clamped and face glued one on each side of the 2x8 I-beam web, and ringshank nailed one on each side so they formed an "X".
I just finished using 14 sheets of Sturd-i-board decking, subfloor adhesive, and ringshank nails. I am amazed at the solid feeling this floor has. I weigh 275, and when I jumped up and down, the only tiny flex I could feel was if I happend to come down on the plywood between the I-beams.
How does this type of I-beam construction with the addition of the 2x4's-16' "X" figure using your spreadsheet? Your insight, please.
Bill
Just Bill,Very cool. What sort of glue did you use? If the bond holds, your floor should be about as stiff as one framed with 4x11's would be. 275# jumping on midspan is quite the field test!Bill
Bill,
You've made an interesting joist, to say the least. ;)
Ignoring those diagonals, I can tell you that you increased the bending strength of the 2x8s by a factor of 5.26 just by applying the 2x4 flanges at top and bottom. That's theoretical, of course, assuming that you have a perfect glue bond between the web and the flanges.
In case Boss needs these numbers for his frequency analysis (or whatever it is his spreadsheet does), the "moment of inertia" of a 2x8 is 47.6 in^4, and your I-joist has a moment of inertia of 251 in^4. (Again, these numbers ignore the 2x4 diagonals on the web). In case you're interested, a 1-1/2 x 10-1/4 joist would have an I-value of about 135 in^4, so yours are nearly twice as strong due to the added width of the flange.
Looking at the joists with the diagonals, the bending strength is actually going to vary along the length of the joist. The way you laid it out, the maximum bending strength will be nearest the supporting walls, and the minimum bending strength will be right at midspan (the opposite of what you really need).
Fortunately, those I-joists are very stout even without the diagonals, as I'm sure you already know without me having to tell you.
I'll be interested in what Boss says about them, too.
I can't decide if you're a dumbasz or a just a dick...?
Why do you have to choose?
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"he ot the placed closed down whyyy thhhattt nnooo gooodddd" - sancho
Because if someone is a DA then you can forgive them being a dick.
Also plan on strapping the bottom o the joists together at 1/3 span per the APA document "Construction Practices for Wood I-Joist Floor Vibration Retrofit".
http://www.apawood.org/level_c.cfm?content=pub_joi_libmain
One thing that I've never seen mentioned is what I might call "relative bounce". The bounce of a specific joist may be well within "reasonable" limits, but if it runs parallel to a joist or whatever that doesn't bounce at all, AND if you place, eg, a curio cabinet on top of the floor between the two, you can have the sensation of bad bounce, as the curio cabinet rolls forward and back and everything in it rattles.
So where a joist runs parallel to a wall, it may be worthwhile to double up on the joists, or at least pay extra attention to blocking. (And note that this is an area where blockiing may be omitted because it's too inconvenient to install.)
Anyone has an opinion on 12" oc instead of 16" oc floor joist? Is it good or bad? Thanks.
Well, closer will always be better for the same size joist, but also more expensive, and it makes the mechanicals much more difficult.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Spacing the joists closer together will typically work to reduce deflection to within spec. However, in general terms, deeper joists at wider spacing result in less bounce/vibration than shallower joists at denser spacing.
And like Dan said, the denser joist spacing can make running mechanicals more difficult.
Sure. Doubling up joists doubles strength, but doubling the height of the joist roughly quadruples the strength, IIRC.
But as I was pointing out earlier in the thread, you may only need the added strength in certain areas, in order to control bounce.
Edited 8/23/2007 6:48 pm by DanH
Since bending strength is a cubic function of the depth of the joist, doubling the depth would actually increase bending strength by a factor of eight.
Lots of bang for your buck when increasing joist depth. ;)
Yeah, couldn't remember whether it was squared or cubed.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
couldn't remember whether it was squared or cubed
The mnemonic I use is "centroids cube." Just about any change in centroid location has a cubic effect from changing the moment arm distances.
Now my father, who is still a brilliant mathematician (all learned analog) remembers these things by remember the the curve order you graph by. Moments are third order, ergo you cube.
Me, I'm happy if I remember to wake up breathing in the morning.Occupational hazard of my occupation not being around (sorry Bubba)
From direct, recent experience, 19' with 11 7/8" 16" o.c. will feel very *live*. I would go to 12" o.c. or a deeper joist.
Jeff
Acceptable floor performance is a subjective thing, but here is another way to think about it (in a very basic way):
A 19' span at L/360 allows .633" deflection.
A 19' span at L/480 allows .475" deflection.
Do you think either of those would be acceptable to you?
Also, when comparing projected performance #s, be sure that you know if #s are for live load, total load, etc.
Call Penner Building Centre (905) 468-3242, Ask for Darren Ward or John Redikop. These guys are great and really know their stuff. Tell them Dave Bevington referred you.
Good luck
Dave