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I am working on a project that has three 2x12’s supporting a load of 12,000 lbs. similar, but not exactly, to how joists support a house.

The 2x12’s are supporting about 6,000 lbs. on each end.

The three 2x12’s are: a) Each cut to 90in.

b) The load takes up 24in. from each end of the 2x12’s leaving 42in. of free space in between.

c) The three 2x12’s are spaced parallel to each other, with one 2x12 being 24in. in front of the other.

d) The 6,000lb. (On each side) load is laying on a thick wooden plank (on each end) that is perpendicular to the three 2x12’s. Similar to this picture (I don't know if it will show up in the post) "J" is the joist but in this picture there are 4 joists. enter image description here

e) The two thick wooden planks on each end of 2x12’s (mentioned in “d”) is securely fastened to the 1.5in. part of the 2x12’s, as well as having blocking and other bolted wooden members that leaves (as stated in “b”) 42 in. Of free space in between.

f) The three 2x12’s are only 12in. off the ground.

Everything is stable and strong without any issues except for one.

I need to lift this so that it is 14in. off the ground (lifting it 2 in. in total).

Removing the load; as well as dissembling is not an option.

This will have to be lifted with the three 2x12’s and everything above (including load) remaining intact.

My best option is to lift (with a hydraulic jack) the front most 2x12 to 14in. and then lift the back most 2x12 to 14in. -I’ve done this before with no problems.

The only problem, that I have now, is that directly under the 2x12 is things that I can not remove and is not strong enough jack it from.

The saddle of the jack is 2-3/4in. All wood is Kiln-Dried Douglas Fir #2 or better.

My plan is to grade 8 bolt a 4x4 cut to 7in. directly in the middle of the free space, mentioned in “b”; plus having the 4x4 cut to 7in. will provide more of a direct clamping force the will be directly in line of the upward force of the jack and the downward gravitational force of the joist when it is being jacked up.

This 4x4 will be bolted to the outward face of the 11.25in. part of the front most and back most 2x12’s.

Questions:

Do you think is strong enough to support the load plus force of the jack or do you think it will just rip the 4x4 off of the 2x12; while also destroying the face of the 2x12’s?

P.S. This project is a hoppy type of thing I am doing and it is not anything that "construction" related.

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  • The load on each 4x4 will be 3 tons which will be on a single 2x12 at each side. Since the jack is offset from the joist, lifting the platform using this setup will exert rotational force on the joist resulting in it trying to twist inward to the center at the top. It may be necessary to provide solid 2x12 bridging across the three joists at the center line to prevent the rotation.
    – Ashlar ♦
    Nov 29, 2020 at 0:27
  • To preface, I've read all the Comments below rjuzzle's Answer. I think there are two critical things here — the integrity of what you're lifting and the actual stress you're putting on the grade-8 bolts. I know you've indicated that the structure is solid, but this still feels like you're putting a lot of strain on it so my gut tells me it should be lifted a bit on one end, wedged in place, lifted the other end, wedged in place etc. until at final height. Also, your estimates/calculations may be off on the load the bolts will be subjected to, which could therefore become the [contd]
    – Graphus
    Nov 29, 2020 at 8:53
  • ...critical element. But (and I'm sure I'm not the only one) I am struggling to get a proper mental image of this without at least a rough sketch to go on.
    – Graphus
    Nov 29, 2020 at 8:53

2 Answers 2

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You've got hydraulic jacks - even cheap ones will lift 2", so lift height isn't critical, so don't try to put your 4x4 vertically - that could be wobbly as it moves during the lift, and it concentrates all the lift force at one point on your structure.

  • Lay 2 4x4s down sideways so that they cross all the 2x12s near each end.
    • Leave clearance for the existing supports and the future supports
  • Use hurricane ties or joist hangars (with appropriate nails or screws) to attach the 4x4 to each 2x12
    • This is to prevent movement, not to resist lifting force.
    • All the weight is transferred directly wood-to-wood and you're not counting on any piece of hardware resisting the sheer force of the weight above.
  • Put one jack at each end of the 4x4, 1 or 2 joists in from the edge and directly under a joist
    • This will spread the force across all the 2x12s while putting the most direct force directly under a joist.
  • Do the same at the other end of the joists.
  • Enlist some friends/family to operate all 4 jacks at the same time and same speed to ensure all lifting happens evenly to prevent racking of the structure.
  • Jack it slightly higher than the final height.
  • Set up the new footers/foundation/final supports
  • Lower onto the new supports and bolt/lag/nail into place.

This will give you 6 tons of weight plus the weight of the structure itself spread across 4 jacks. Theoretically, each jack is only taking about 1.5 tons. If you get four 6-ton jacks (which you can pick up pretty cheaply at the store that goes to the Harbor to get their Freight, or any automotive store), you'll have more than enough jacking capacity.

If the jacks at full extension don't reach the height you need, support each jack on some 2x6(or greater)x12" cuts stacked (and nailed/screwed to prevent movement) until the compressed jacks just touch the bottom of the 4x4.

I used a system similar to this to hold up our porch roof (on a 6x6) when we tore out the porch & columns below it to rebuild them. Supported some 2x10 on scaffolding, put the 6x6 on top of that, worked the jacks under, lifted the roof, put 6x6 support posts under it, released the jacks, removed the scaffold. Worked a treat. Used jacks from the aforementioned store with no problem - for the few extra bucks, I got two 12-ton jacks - significant overkill, I'm sure, but they held with no worries.

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I would probably go with a 6x6 and notch out two of the faces, without doing any math. Takes the weight from the bolts and allows them to provide clamping pressure only. Hard to say for sure without knowing exactly what your doing. enter image description here

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  • This won't work because there are things underneath the 2x12's that cannot be removed.
    – John
    Nov 28, 2020 at 21:47
  • Then I'd say your critical numbers are the shear strength of the bolts, that will most likely be the weak spot.
    – rjuzzle
    Nov 28, 2020 at 21:51
  • Before I would just slide a jack under the first 2x12 and jack it up to the desired height and slide in something, like a jack stand to keep it at that height. Then I would go the the back most 2x12 and repeat the process BUT NOW I can not do this because there is stuff (that cannot be removed) in the way. So I believe the only option is to do the process I mention in the original post; which leads to the question I have in the original post.
    – John
    Nov 28, 2020 at 21:51
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    As stated without more information it's impossible to say for sure. If all your numbers are right, you can rig it up, take the load up a couple inches and get a feel from there. Make sure you have blocking in hand to slide underneath.
    – rjuzzle
    Nov 28, 2020 at 23:06
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    I doubt anyone in their right mind would say 100% it will work. And if they do, I would ignore them. It's going to have to be a risk you take on. The idea is sound, the numbers for the weight distribution seem off, its probably going to be higher that half the total weight for the point load if its rigid and your that far in from the ends,I would estimate at least 8000lbs. Also if the structure is that sound, by slowly taking up the weight, you'll get a feel for what it is going to do.
    – rjuzzle
    Nov 28, 2020 at 23:34

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