I am looking for advice on leveling a floor system. The joist are 2×4 top and bottom chord and are spanning almost 29′. The company that designed this job is out of business. The underside of this floor is a garage that could have a beam placed down the middle without much problem of course with engineered footings, poles and beam. My question is, will the open web joist lift from a center point ?. Some of these joists are 1′ center at the 30′ span and some are 16″at the 27′ span. I can also install a squash block above the new beam. So far I’ve had no luck with local truss companies wanting to get involved with this. Any advice or similar experiences appreciated. In the mix of this floor system is a pair of LVLs that have also sagged that are carrying a bearing wall.
Edited 7/12/2008 3:37 pm ET by shellbuilder
Replies
depends on where you are in the food chain...
if this is for a customer, i'd seriously think about getting a Structural PE to come up with the fix
on the other hand... if i were there looking at it , I might decide to go ahead anyway with some shade-tree engineering
it does seem like cutting the span in half and taking care of point loads should be the cure
I agree. Any structural engineer should be able to analyze the design and offer the engineering for the fix. The sagging lvl is easy...add more. The spans on the web sound easy too once the beam is in. If it were my place, I'd just start adding beef till it was solid. Bob's next test date: 12/10/07
The engineering time is likely to be less than $300 and could easily save more than than in shade tree engineering and it's attendant overbuilding. Bring in the expert and ask for an elegant solution.
That said I will sometimes propose and do cost estimates for a couple of options before I call the engineer. It's good for him to see my preferred choices and their attendant costs so he can pitch the most economical option that best fits my preferred method of work.
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"You cannot work hard enough to make up for a sloppy estimate."
"...will the open web joist lift from a center point ?"
Nope - It ain't that easy. Adding a center bearing changes forces all around. The truss may need to be beefed up in places you wouldn't expect.
As others have said, a PE familar with wood trusses may be your best bet. A truss company that didn't build the trusses won't want to get involved in this for liability reasons.
How deep are the trusses?
21" tall joists spanning max 27'. LVL spans 24' and carries a exterior wall where the front wall was inset to create a covered porch, so its a in the mix of the joist This is my own house, when I built this house I asked the engineers to upsize the joists and unfortunately that obviously didnt help. There is a see thru fireplace with some cabinetry flanking it with stone tops in the center of the 24' span. This area and the recessed front wall (the shorter spans) is where I'm seeing sag and problems with the doors going to the covered porch. I was involved with a job 10 years ago trying to jack up LVLs and they wouldn't go , the ends actually lifted and all were replaced with steel.
I stuck a 6x6 on a 20 ton hydraulic jack a few months ago under the LVLs to see if I could get some up movement and the jack wouldn't budge it. I probably pushed the garage slab down some trying this. Any advice is very appreciated!!
Edited 7/12/2008 7:37 pm ET by shellbuilder
In the first post you said the floor trusses span 29'. Then you mentioned a 30' span. In the last one you said 27'. What's the deal?Are you sure they're 21" deep? I don't see many truss companies making floor trusses in odd depths.Keep in mind that with typical deflection standards (L/360 live, L/240 total) a 27' truss is allowed to have 1.4" of deflection. So your trusses may be withing what's allowable. Are there special point lods on the trusses? Any chance of getting pictures of them?
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My mistake on the spans. The first dimensions were outside spans on block walls. They are 21" tall, at this point there is no access to take a picture, its all finished. The 1.4" deflection....... that's not good. At this point it doesn't matter where the problem started or ended. I need to jack up the LVL that is supporting a wall with 3 patio doors leading to a deck that are showing a problem. If the LVL will go up and the adjacent floors will go up then I have success. The other scenario would be the joist lift, crush at lift points and the LVL won't budge because i can't provide documentation. These joists are also full of ductwork and wire.
Edited 7/13/2008 10:26 am ET by shellbuilder
Sometimes, you have to concede the sag but beef it up to stop further damage. Once it's beefed up enough, it becomes a blend job. Bob's next test date: 12/10/07
The LVL can probably be jacked up and straightened out. But the sag that's in it was put there over a long period of time, and will also come back out very slowly. It might take jacking it up 1/4 turn evrey few days for a couple of months.As for the floor trusses - No fix that an engineer calls for is gonna be easy. If you put in a mid span beam they will call for some plywood gussets at some of the joints. Obviously that will be difficult when you have wiring and such running through there. And the fact that the space is already finished will only make it more difficult...
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I was thinking that after he put the steel in, the spans would be small enough to sister in 2x10's. He could just ignore the trusses. Bob's next test date: 12/10/07