Making a beam from oak

[John T]

In my basement, there is a metal post giving additional support to a beam (not load bearing, but doubled) where the fridge and stove are side by side on the first floor. This post is in the way of woodworking operations. I dunno if the floor here would sag or not (I kinda doubt it) without the post. I've intended to buy a 4" I beam to put under the wood beam with posts at the end, but it occured to me, why not laminate a beam myself?

I've got loads of oak planks. I could laminate 4 pieces full length that I need (about 10-11'). Or would I be better off making one out of ply with staggered joints, or spending the bucks for the steel beam?

As I mentioned, I don't think the post is really needed, but the beam wouldn't have to all that strong either.

Thoughts?

John

[fredfighter]

Uh, that means it is load bearing. It may not be bearing a load imposed by the house, but it is still bearing the load imposed by the refrigerator and the stove.

Sounds like a double joist. Joists are beams that support a floor or ceiling. Joists are doubled where one would be inadequate. Extra posts are put underneath to cut the spam when a double joist is inadequate and/or a larger joist inconvenient.

It will certainly sag more without the post than with it. How much more is the issue.

Architects and builders do not put posts in randomly. If that post is called-for on the blueprints it almost certainly is needed. It it was added later, I'd still presume it was needed to correct a problem.

The post now cuts the span of the double joist, probably to half what it would be without the post. It may be that the existing double joist was only slightly inadequate over the full span, you need to do the arithmetic to know, or at least check some tables of joist size vs span, which you can find online.

I suggest you read up on beam theory. You can find plenty of material about beam theory online. What you have in mind is probably doable many different ways. You just have to know _how_ to do it right. Even if you wind up working from tables, knowing the underlying theory is a big help.

Another consideration is whether or not what you have in mind will meet code.

[Earl Creel]

If I understand your situation correctly your existing beam only spans 10 or

[Todd Fatheree]

First, I suspect that the post isn't really needed if the floor joists were properly designed in the first place. Proper joist design per code factors in live loads that would account for things like refrigerators and ranges. However, since you're considering steel vs. oak, I can give you some comparative numbers between them. If anyone wants the details, I'd be happy to provide them, but for here, I'll just cut to the chase.

Joist design generally revolves around limiting deflection. Now, there is also the question of strength, but I suspect that codes figure that by limiting deflection, the stresses take care of themselves. Consider a standard 4" steel I-beam. I have the values for an S4x9.5. The moment of inertia (I) for this beam is 6.79 in^4. The modulus of elasticity (E) for A36 steel (a common structural steel) is approx. 29,000 ksi. E for red oak is approx 1800 ksi. In order for the deflection under the same distributed load to be the same, (Esteel/Eoak)=(Ioak/Isteel). We know everything but Ioak. Solving for Ioak, we get Ioak=109. For a rectangular cross-section, I=(bh^3)/12. Assuming the height of the beam is 4 inches, we can solve for b, which would be the width of a red oak beam required to match the deflection of an S4x9.5 steel beam.

109 = (b x 4^3)/12

b = (109 x 12) / 4^3 = 20 inches.

Again, I suspect the post or this beam isn't required, so long as the floor was designed properly and per current code in the first place, but this gives a point of comparison between a steel beam and an oak beam.

todd

[Toller]

You would have to crazy to ask for advice about that here!

[Sam]

Slip a few more joists up besides the ones already there and then you won't lower the headroom. Sam

[Phil at small (vs at large)]

When I built my downstairs ( had an upstairs house-- AKA Jim Walters) I needed to remove one of the 10" posts for my living area. The beam was a pair of 2x10's spaced about 6" apart supported on 7' centers. I checked on the cost of an i-beam which was astronomical, plus the engineer said I'd have to use a 14" beam-which would reduce my headroom in that area- Long story short-- I jacked up both sides of the original beam & put in 6 more 2 x 10's -- BTW span is 14'-- Kinda figured I'd over done it a bit. Gang nailed the hell out of it & the new beam is sitting on 4-2 x 10's at each end, nailed to the original

10" posts. 10 years later there are no SR cracks & the floor above is solid as a rock= just my experience. Phil

[John T]

This post is not original to the house. The house was built in 1902, and all the other posts under the load main bearing wall are wood. There are no other posts under this beam except where the load bearing wall crosses it.This post is metal and was added a few years ago. The fact is, the stove and refrigerator have been in this area for decades, i'm sure. I have no idea why my dad put this post in (I bought the house from my mom a few years ago).

The main load bearing wall runs perpendicular to this one. Now that one is BIG.

I'm not concerned about the loss of a few inches of headroom. I need the space for manauvering the TS more than the headroom. :)

John

[fredfighter]

OK. In 1902 they didn't have refigerators and I dunno how heavy iceboxes were so maybe your father noted a little sag in the kitchen floor or something and added the post. At any rate, it sounds like at worst the joist was almost adequate.

Seems likely you could nail another joist or two on making it a triple or quadruple joist and then remove the post. Whatever you nail on, it should be continuous from end to end. If it is segmented, the worst place to put the gap would be at the center. If the added-on joist is less than the full depth of the existing joist, which is likely, making it flush with the bottom maximizes the strength of the reinforcement.

[Stephen M]

Huh? my whole shop sits on 4" wide by 12.25" steel beam. The span is 24'. I was told that the weight was about 600lbs. It cost me about $260 plus about that to have the crane deliver and install. A 14" beam for a 14' span doesn't sound right to me.

-Steve

[Charles Spitzer]

what was the code in 1902?

[Todd Fatheree]

I have no idea. However, assuming you can read English, you'll see above that I stipulated for my comments that the existing floor had to be "designed properly and per *current* code" since the age of the house was not provided in the original post.

todd