Got a buddy who has an 8 yr old 2 story home in MN. Kitchen has considerable changes in elevation, and I volunteered to have a looksee ( having done the housejacking thing before.)
Under the kitchen we have a fairly accessable crawlspace with ~ 3.5 feet of headroom. There are two in-line east-west beams that span 18 ft and 20 ft, respectively, and they are in the block wall on each end, meeting in the middle at a “post”.
Post is in quotations, because the builder used 3 PT 2x6s sandwiched together as a post. They go through the poured concrete floor, and must be on some kind of a footer. The 5.5″ dimension runs east-west, in-line with the beams.
The two beams…One is three 1.75″ x 12″ LVLs spanning 20 feet, and supporting the floor above and its roof (no 2nd story). It appear to be in good shape, although it overhangs that post by 3/8″ on either side.
The other beam has problems. It’s two 1.75″ x 12″ LVLs spanning 18 feet, and it carries the load of the kitchen appliances/cabinets and the second story + roof. About 5 feet from the post, right below the ‘fridge, is the low spot of the kitchen floor and the sag. The LVLs have sagged ~1 1/4 inches there.
And finally, the top of the post itself seems to be about 1 1/2″ lower than it should be. Not sure if the footing below has allowed some settling or if the PT 2x6s have compressed/shrunk, but either way, that has to be fixed.
So…. What to do? My inclination is to get the bottle jacks in there (appropriately supported) and give it a lift. Replace the existing post with metal. reclaiming that lost 1.5″. Either cut the 2x6s flush with floor or possibly pull them out of the concrete entirely, if possible. Thoughts here?
Then, the LVL sag. I think we need to cut open the floor, and put in a new footing and a new post under the low spot. Not sure how well LVL “unbends”…can we expect to jack that low spot up and have it go level again, or would jacking the low spot bring the end up off the post? Or are we just doing this to prevent further sag?
How big a footing (frost not an issue; middle of the home’s footprint)?
I have told my friend to expect other problems with jacking, wall cracks (which he has anyway as a result of the sinking) and who-knows what else (plumbing comes to mind). But considering he has doors that are having trouble opening, our concensus is that the cure is likely better than the disease. He plans to stay in the home a long time.
Any thoughts appreciated.
Replies
Just to make sure I understand right - The beams both have a "post" in the middle? The beams aren't clear spanning the 18' or 20'? Or do they clear span the 18' and 20' to meet at one "post"?
Also - Why can't you see if there's a footing under the post(s)? Is there something in the way?
Boss-
Knew I did not explain well enough...The two beams butt end-to-end with each other, and are supported by the same 2x6 post. One clear-spans 18', the other clear-spans 20'.
Those three 2x6s run straight down through the poured concrete floor, so to see what they rest on will require some concrete removal. There must be something substantial there, or the sinking would be far more dramatic.
Edited 5/17/2004 2:50 pm ET by snsteury
I'm not an engineer, but it sounds like your beams are undersized, and there is not enough bearing at the post ends. I have an 18' beam in my house, made up of 3) 14"LVL, that holds up the second floor and a point load from the roof at about 5' in from one end. Allowable deflection was 7/8". I think the bearing at each end was 3" minimum.
A few years back I took out 16' of structural wall (holding second floor only) on a project, and put in a beam. The post on one end was on the foundation, the other post required a 24"x24"x12" pad with 1/2" rods in the bottom third of the pad. This was speced by an engineer.
Might be a good idea to have this repair engineered.
I am in East-Central Wisconsin so our roof loads should be similar.
Edited 5/17/2004 3:07 pm ET by Bowz
That explains a lot. No way should an 11 7/8" LVL span 18', much less 20'.
I'd definitely add one post and footing under the 20' beam, and 2 posts and footings under the 18' one. And fix the footing where the center "post" is.
Soinds like they did some "HOH" engineering. That's where they throw something together without having a clue what they're doing. Then they stand there with their Hands on their Hips and say stuff like: "Looks good to me" or "That ain't goin' anywhere".
Footing sizes are beyond my expertise. The typical ones I see are 2' square and one foot deep. That may or may not fly in your area.
.
When I hear of something like this, it makes me wonder what other surprises might be hidden in the house somewhere...Power does corrupt. Just run a good cross-current past your data cables, you'll see. [Ari Rapkin]
LOL, I was thinking HOH meant Help of Heaven engineering, which had to be what the original builder was counting on. my eyeballs rolled up at seeing 12 deep for an eighteen foot span with all that load. maybe they thought they were working with steel!
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Left o9vers or bad cuts from anoher job... Too much faith???
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming.... WOW!!! What a Ride!
Where's it gonna go?
It has already gone DOWN an inch and a half and developed an additional sag!
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
That explains a lot. No way should an 11 7/8" LVL span 18', much less 20'. Boss, you might be right, but I think you missed a detail...one beam is three ganged LVL's and the other beam is two ganged LVL's.Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
Still far too small. Last time I remember off top of my head for similar situation about a 17' span used three 2x14LVLs
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Still far too small. Ok...just wanted to be sure that wasn't overlooked.Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
"I think you missed a detail...one beam is three ganged LVL's and the other beam is two ganged LVL's."
Once you reach a certain length/depth ratio, it doesn't matter much how many plies you have. Once you get past 14' or so, the value of an 11 7/8" LVL drops off sharply.
That's why I said: No way should an 11 7/8" LVL span 18', much less 20'Every Act of Authority, of one Man over another for which there is not an absolute Necessity, is tyrannical. [criminologist Cesare Beccaria]
I just went into my own basement, for curiosity's sake, and I have quite a few LVL spans. But they are all fairly short; for instance: 14" deep, 10.75 foot span, and they used 3 of 'em. As I was measuring, I noticed that there was also a male turkey in full strut right outside the walkout door, but that's another thread.
Looks like my underbuilt amigo will get some new footings and posts.
The one question nobody directly addressed...will we be able to unbend/flex the 2 LVLs that sag at the 5 foot mark on a 18' span? Or it that not likely?
"...will we be able to unbend/flex the 2 LVLs that sag at the 5 foot mark on a 18' span?"
Yup. If they've bent one way, they'll bend the other. Just go slow.Praise the Lord and pass the ammunition. [Howell Forgy, 12/7/41]
Yeah, I think the LVLs will unbend when properly supported. To take that much warp out you should spread the lift out over a week or so, and watch things to make sure nothing up above starts coming apart. Be especially wary of any plumbing in the area.
At risk of again showing my inexperience... I was recently looking at a GP chart that showed their 12" wood I joists suitable for like 19 foot spans at 16" oc. (500s series, with L/480 deflection) Should these charts not be trusted? I recognize this conversation was geared to LVLs, but the general horror at the span made me wonder...
Paul
Edited 5/18/2004 3:08 pm ET by PaulB
Ever read the Floor Vibration thread? That will give you a lot of info on floors performance.
Beams and floors are not the same. I like to see 11 7/8" I-joist spans limited to about 18'. But I try to avoid using 11 7/8" LVLs when they span more than about 14'.
Granted, I'm a bit conservative on things. But that's my opinoin, and it's worth every penny you paid for it. (-:Remember, Ginger Rogers did everything Fred Astaire did, but she did it backwards and in high heels. [Faith Whittlesey]
Thanks for the comments... I am working on laying out an addition for a friend and was using the GP span charts for sizing so I was concerned. I'm basing my plans on their "Four Star" table, which provides L/960 deflection and a "much stiffer floor for the discriminating purchaser" ummmm... yeah... hope it's true
Paul
Your proposed repair sounds fine. Do you have a 20-ton bottle jack and four big screw jacks? I'd get in there and try to lift things a bit, in the center where the two beams meet (two lifting points, one on each side of the splice) and in the middle of each span. Lift each point a little with the bottle jack and then put a screw jack in place. Leave it a while and then go in and raise it a bit more. I would not go the entire 1-1/4" to 1-1/2" that you mention all at once--maybe go that far in 4 to 6 small lifts. You're going to need to bust out concrete around that center post and find out what's under there. You'r probably going to have to remove 100% of whatever it is and then re-pour your own new pier, and I'm guessing a 24" sonotube with some #4 or #5 will do. Make sure you're on undisturbed soil and if it seems wet in the hole then there's another problem entirely. Pour your pier above the level of the floor and then patch the floor up to it with an expansion joint around it.
The original builder went cheap on this. Sounds to me like two intermediate supports (dividing the 38' into thirds) would have been a helluva lot better. You could also do thirds if you want to leave the original center pier in place--jack things up, pour two new piers at the 'thirds' points, and then span the center third where the beam splice is with a pair of 13'+/- steel C-channels laid alongside the LVLs and bolted thru.
I've been in a crawl space quite a lot lately, and it's good to know someone else it taking over!
I recently installed a double 9 1/2" LVL spanning only 9" and the spec required a 5 1/2" bearing at each end. According to your discription you have 2 1/4" bearing for each beam in the center - ouch!
i don't think a ref. alone will cause the sag. What else is on the joists which run into the beam - 4' from center of sag? Most likely your culprit will be there.
Go to Georgia Pacific http://www.gp.com/build/product.aspx?pname=G-P+Lam¯+LVL&pid=1392&hierarchy=pc and scroll to the bottom of the page. You will find PDF's for length bearing specs, load specs and.........
One more thing, cutting the triple 2x6 wood column flush with the slab and then placing a steel column in its place won't change things much. The load will still be transfered to the footing via the trple 2x6s in the slab. So far we have discussed bearing but how about focusing the load ie: bearing for each beam = width of beam x 5 1/2". This load is then transfered below to an intermediate bearing/ column cross section of 4 1/2" x 5 1/2". I don't know if this is acceptable.
Let us know how things go.
F.
I think what I would do is:
1) Excavate and pour a new footing near the low spot (though maybe a little closer to the middle of the span). Also consider doing the same on the other side.
2) Jack up the whole shooting match using at least 3 and maybe 5 jacks, with one each side of the existing post, one or two under the sagging beam (either side of the new footing), and maybe one near the middle of the other side. You'll need solid bearing for these, and it might make sense to pour some small (1-foot-square by 4" thick) footings for them while you're doing the "real" footings.
3) Get the ends of the beams off of the existing post by the 1.5" plus a smidgen. Craft an appropriate shim to take up this slack. Consider scabbing more 2x on the sides of the post (with carriage bolts or lag screws + urethane glue) to increase the bearing surface for the wide beam (but not really clear this is needed).
4) Jack up enough to bring the sagging LVL to near straight, then install a post on the new footing.
The new footing, and possibly one on the other side, will remove enough load from the existing post that it will probably stop moving. If it continues to move in the future it can be replaced then -- no harder than doing it now, and no sense doing work you don't need to do (especially when it involves excavating in a crawlspace).
Clear spans that long in a crawl space are really bizzare. And this wasn't a cheap way to go. Dimensional lumber with a post every 4 ft. would be cheaper and a lot stronger than those big expensive LVL's. Dividing the spans up with new footings and posts is a good idea. But when something that strange has been done, I'd get a professional opinion not only on the specific fix, but also on the rest of the structure. Pay an engineer or an experienced contractor to look at it in person.
-- J.S.