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Discussion Starter · #1 ·
Hi! I just added an 8 foot beam, resting on two 4x4 posts that are about 6 feet apart, under my dining room floor. I'm going to put a 180g aquarium there and I don't want the floor to sag under ... 2000 lbs of water.

I dug footers down about 9 inches x 16 inches wide and used premixed concrete (with rebars) and embeded into that were pre-formed concrete piers. The piers have metal straps embded in them, which I will nail into the posts. I used simpson metal post caps between the beam and the posts.

Now After I put the beam up, which required some encouragement with a hammer, the posts are quite snug, and just above the posts the joists are touching the beam. As I go towards the center of the beam, the joinsts are not touching the beam. Oddly, on one cantilevered side, the joist doesn't touch there eitheIr.

Oh, maybe the beam is warped! So I flipped the beam over (man, that was work!) and reinstalled it... same thing! So, OK, the beam is sagging from it's own weight? It's an 8 foot long 4x8 beam with the posts approxiamately one foot in, so the beam spans around 6 feet between posts.

Is this normal? Is the beam sagging or the joists not equal sized (doubtful, but then again the house was built in 1939, so who knows).

I'm NOT going to put another post in the center unless I really have to, but from what I've read, 6 foot beam span on a 4x8 is no big deal. (more info, the joists are about four feet to the foundation on one side, and 6 feet to the main house beam on the other)

So since my miter saw was set up from cutting the 4x4 post, I just took some thin slices of the 4x4 to use as shims between the joists and the beam. 1/8" on two shims and almost a 1/4 inch on the joist in the center of the beam.

So (finally!) my question is ... is this OK to use shims like this? From what I can tell, as long as there is a load path from the floor to the joists to the beam then it's hunky dory. If I don't shim, then the joist would sag down tot he beam, right? Is that sag in the beam OK? Is 6 foot beam span OK? And ... should I install a third post in the center?

OK, those are my questions! If necessary, I'll go take some pics.

Thanks!

Vince
 

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Just shim the joists that are over the support beam and not touching.
Ron
 

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Discussion Starter · #3 ·
Thanks Ron. Is it OK to just use slices of the leftover 4x4 post material as shims? Should I use tapered shims, or just hammer home some flat slices of 4x4? Should I use metal?

Thanks!

Vince
 

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sight down the beam from one end. if there is any curve to it put that on the top side. framers usually crown joists like that when they install them. the hump goes up. if the beam is perfectly straight then you have to shim. i cant see the beam sagging in that short of a distance
 

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Thanks Ron. Is it OK to just use slices of the leftover 4x4 post material as shims? Should I use tapered shims, or just hammer home some flat slices of 4x4? Should I use metal?

Thanks!

Vince
I would use tapered shims, inserted on each side per shimming station. This way you don't need to measure each gap.
You can use composite shims, or pine shims they sell. Or make your own from southern yellow pine.
Ron
 

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Discussion Starter · #6 ·
I would use tapered shims, inserted on each side per shimming station. This way you don't need to measure each gap.
You can use composite shims, or pine shims they sell. Or make your own from southern yellow pine.
Ron
OK, the 4x4 I'm cutting mine from now (and measuring) is douglas fir, is that OK? I figured...heck, the post and beam are made of doug-fir, why not the shims?

I'm also cutting them such that the grain runs vertically, so that weight will go along the fibers of the wood as oppossed to crushing the wood grain from the side (ie crosscutting 4x4, not ripping)

Thanks Ron, your advice is appreciated as always!
 
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