Rebar

My second vote goes to the 10"-10" x 5"-10"-5" arrangment of the rebar as suggested by another.

KEG

This morning I got some 3/8" rebar and 3/8" mild steel rod, beveled ends to points and welded butt joints with 3/32 7018 stick. I also butt welded pieces of 3/8" rebar with one beveled end against a flat end, and two flat ends together. I ground off the welds until they were the same diameter as the rest of rods. When I was finished, I had 1 mild steel rod and one length of rebar with double beveled butt joints, and 2 other lengths of rebar with beveled to flat and flat to flat butt joints.

I put each piece under the 90 degree bender of an 80 ton press and bent at the weld to about 135 degrees (in other words, halfway between the 180 degree straight rod and the 90 degree bend the press was capable of producing.) The mild steel rod showed pre-separation stress but no actual tearing. The bevel to bevel rebar showed a stress crack without visible separation. The bevel to flat end rebar and flat end to flat end rebar both tore almost entirely through, and broke with negligible hand pressure. The cracked but untorn rebar broke with moderate hand pressure, the mild steel rod with slightly more. By hand pressure I mean holding a rod at each end and trying to snap it like a piece of kindling. Any child could have broken either of the cracked pieces; a weak adult might have had trouble breaking either of the other two.

That's it, for what it's worth.

Stan

You talked about it being six of one, etc. as far as whether it made more sense to weld or wire your rebar. I ran into the same sort of problem when I was forming up a long retaining wall on two sides of my property. I had plenty of rebar but I hate wiring up that stuff. I always seem to end up with about two bleeding rips on my forearms and two puncture wounds in my hands per 25' of forms.

I made a couple of 50' 6/3 extension cords and dragged an arc welder along the work. I enjoyed it much more than tying wire, but there was probably no time saved. A definite benefit to welding your metal is that it doesn't shift and slip when you're working around it. I've never been able to get enough of that soft wire on my rebar, or twist it tight enough, to keep the metal from slipping some as I did other work on the forms. The welded stuff stays right where you put it.

I was fooling around with some 3/8 rebar this evening, trying to see what kind of butt joints I could get with oxy/acetylene. Poor, I have to report. When I used the hydraulic shear to cut off the welds, the rebar was noticeably brittle within the whole heat affected zone.

I guess I'm going to have to do some research on steel reinforced concrete. To some extent I can visualize the physical forces which bear on materials in uncomplicated configurations, but I'm at a complete loss to imagine how shear, and tension, or the effect of brittleness or other qualities of the metal affect rebar which is encased in concrete.

The reason I go on about this is because even if some grape grower got the rebar you were going to buy, you're still going to pour that slab. That means that you're going to be dealing with these same issues pretty soon---only with some other rebar.

All the best, Stan

I got my introduction to placing rebar with my first house, the one I'm still living in. It's underground with the back wall holding 15' of dirt. Got engineering and the guy I almost hired for the walls wanted $10k (14 yrs ago) to place a couple tons of rebar ($1.5k worth at the time). He told me it took a long time to tie rebar.

I didn't know any better but didn't have the money to pay him so I bought a couple of winders and a roll of twist ties. Guess what? I can now tie that much rebar in about 2 days- by myself, without any injury. Professional guys say the twist ties are too slow, but for those of us who don't do formwork every day, they're a blessing. And exactly what you needed. Next time, find somebody catering to the concrete trade and leave the welder in the shop.

Reason for the rebar is to control cracking in the concrete. If a crack occurred near a failed rebar joint, it might pop loose. Then you'd have nothing to control movement of the crack, possibly catastrophic failure. You need continuous rebar across any crack.

As far as welding rebar goes, there's a large difference between graded and ungraded, like the home centers sell. Graded is consistent, ungraded will have hard and soft spots, making it difficult to weld. All the engineering I've seen for our houses calls for grade 60, an intermediate grade.

The $10K for two days work addresses one of the two ways I feel about engineers. On the one hand I admire the attitude that every problem can be solved and that out of all possibilities there is a best solution. On the other hand, the engineering approach to business seems to be that they will provide the customer with the very best solution, no matter how much overkill is involved, and no matter how much it costs. If you're a big commercial customer, you probably have the clout to argue for just enough engineering to get the job done. If you're a homeowner you're SOL and go into sticker shock, too. The underlying situation is that there is no general designation---engineers, lawyers, doctors, scientists---that assures quality thinking; it's strictly on an individual basis, just like everything else in the world.

All the best, Stan

The building dept here asked who I'd hired for the engineering. Upon hearing, they said that I'd be fine with half the rebar. I said "great, which half?". They said it was up to me, the owner/builder. Now that makes sense. The decision is left to the guy who knows the least.

I bought the rebar.

Don't quite share your view of engineers. As the saying goes, they wear two pair of underwear- just in case. When you buy a drawing from them, they're putting their butts on the line.

A good one will also figure how to save you some money, within his engineering comfort zone. For instance, I built curved walls. Primarily for esthetic reasons, but I also know they're stronger. When I asked the engineer about it, he said he could engineer the reinforcing for my curves and save me some rebar, but it would cost substantially more than the extra rebar he'd spec for a straight wall.

Overbuilt? Probably, but a tiny percentage of the total construction cost. Half the rebar, if I'd chosen not to use it, was all of $750.

The next house was for a client. I was the skill guy, helped by two college kids who knew nothing. After a half hour using a winder, they were tying rebar almost as fast as I do.

Almost all rebar comes from India (duh! who"ed ever thunk of that?)

In India, brokers negoiate all over the world to buy old ships, especially Russian ones. Freighters, warships, etc. They beach them, wench them up as far as possible, and using gantry cranes salvaged from previous ships, began the very dangerous work of disassembling them. The steel hull planks are cut and hauled to a nearby mill where they are run thru and sliced into thin strips. The strips then run thru a hot rolling forge where they are given the familiar rebar crosshatch finish and slightly oval shape. Then they sell it to the rest of the world.

Next time you see rebar, think..... . Russian Ship!!

Charles

I used to be involved on high rise projects in NYC and been around quite a bit of reinforced concrete structures, building components etc. I don't ever recall seeing lap joints being welded, or called for on structural drawings etc., also have to be careful when field cutting steel with a torch although that applies more to structural shapes and connections, the rationale behind it is of the same concern, brittleness, which I can agree might be an issue with welding bar of that size. With the amount of joints that get tied, it would be insane to weld as no one could work close to you. They usually set up a machine that shears and bends the rebar and the Lathers do all the fabricating, tying of the joints and installation inside the form. I can also see the Inspection controls needed when field welded joints are concerned, In NYC, a licensed professional engineer has to inspect and sign off on a technical responsibilty report for all structural connections, especially welded joints, they even go to the steel fabricator to inspect fabricated sections etc. It sounds ridiculus but it's done for good reason, and if properly done from beginning to end on a project, it's no hinderance to the production. Way off here, back to reality as this is for the "Skyscrapers" and like, a lot of the rebar that is placed can be seen with no blue left on it, is rusty, just not corroded with heavy flakes peeling off, I would use that material, tie off the 150 joints you appear to have, use the setting chairs, maker sure the bar has enough coverage above and below, ideally 3" both sides with a 6" slab, but as best can be done. I am a fan of reinforcing, be it rebar and 6"x6" woven wire mesh, W.W.M. the latter I would think in conjunction with fibre admixtures, ought to be a good slab mix, not sure what kind of loading you can get away with, but it's interesting to hear about how it's performed for all the people who write about it here, I've never done a lot with the fibre admixtures. The only concern with regular rebar, not galvanized, epoxy coated or what have you is that concrete has capillaries that allow fluid to seep in, if it is corrosive, and reacts with the rebar, it will expand the steel 3x its size and spall the concrete, as what happened to older bridge decks due to salt used in the winter. Don't mind me lately I'm full of all kinds of wondering babble, overkill etc. LOL, but it sounds like a decent deal I'd use it without hesistation.

I built a retaining wall and used rebar in it and the footers I welded it together that way it stayed put and wasn't moving all over while working and pouring. I never did see any sense in the twisty tire wires what the heck is that going to hold ? I don't even mess with it in my floors and have never had a problem. A good 4" with fiber is all my concrete guy recommends unless you are really running heavy equipment over it.One thing often overlooked is the more uniform thickness that is maintained it helps make it stronger too.

I think the reason that you don't see that often on job sites is that it requires a whole additional level of skilled labor. Certified welders, supervisors, and inspectors all quickly add up in dollars.

I will say that tack welding is not permitted as a substitute for wire ties.

Overlap it and wire it together.

Charles

Rebar in forms is usually wired together, so welding should be excellent---overkill even.

I've read that rusted rebar is better than bright because surface rust gives the metal more "tooth" to be held firmly in the concrete. Flaking rust, or enough rust to weaken the metal is another matter, of course.

All the best, Stan