36" in Seattle

[dmun]

Re: 36" in Seattle

You can also use a couple of lengths of pipe (like half inch black iron gas pipe) as a lever pair to bend lengths of rebar.

[kebwi]

Re: 36" in Seattle

Here's my current plan for the foundation rebar arrangement w.r.t. the first course of concrete blocks. The foundation is a weird shape because it fits into a corner against the retaining wall (see yard rendering and progress photos in my album). It will also have the standard concrete mesh (what is that, about 6" spacing and 1/8" diameter?).

[Neil2]

Re: 36" in Seattle

3/8 inch rebar has a little over half the end area of 1/2 inch rebar. If forno bravo is recommending 1/2 inch at 12 inch spacing with 1/2 inch rebar, you will get the same steel ratio (or a bit better) with 3/8 at 6 inch spacing.

I suggest 3/8 inch because it is a whole lot easier to cut, handle and bend than the 1/2 inch rebar, especially with home improvised tools (grinder and a length of pipe). I even like to use the 1/4 inch rebar but this is hard to get.

As for embedding or overlap I would go with at least 12 inches with 3/8 rebar. Or you can "button hook" the end. The dead end of a straight piece of rebar doesn't "grab" the rebar fully for about the first 12 inches or so. The rebar should always bend around the corner and overlap the next piece - avoid "dead ending" it. Tie the overlap with two pieces of rebar wire.

And again, your local rebar supplier will almost certainly have a bending tool on site for customer use and will show you how to use it. You can also rent rebar benders - they are easy to use. These tools will cut, bend and button hook with precision. Or you can wrestle your rebar with a piece of pipe.

The 6 inch WWF (welded wire fabric) is primary for use in crack control. It doesn't' hurt to throw it in but don't rely on it for structural strength.

I also see on your plans that your are casting an integral approach slab. This will crack in the vicinity of the oven wall. Consider casting this in two steps - this will provide a construction joint so the crack is controlled.

[kebwi]

Re: 36" in Seattle

Everett Steel doesn't bend rebar, although they will cut it for me (which is ironic since I'm not too worried about cutting it with a grinder). They really are one of the only options I've found around Seattle actually.

Home Depot and Lowes (and Ace) have rebar for a much higher price, and obviously don't bend rebar either.

Thanks for the info. It's coming together.

Cheers!

[kebwi]

Re: 36" in Seattle

I suppose one could ask -- although this is venturing deep in academic obscurity -- is it easier, harder, or equally difficult to flex a single rebar of X cross section or multiple smaller rebars whose cross sections sum to X? If flexing the bundle is easier, then the bundle is "weaker".

It seems to me that total cross section is not necessarily directly equivalent to flex resistant strength. For example, instead of rebar, consider flat metal slats (like one side of an angle iron. In fact I see this stuff sold next to angle iron everywhere). Lay the slat flat and it's easy to bend vertically (but hard to bend horizontally). Stand it on edge is it hard to bend vertically (but easy to bend horizontally). This is how I-beams work of course. In their vertical orientation they provide excellent resistance against vertical flex.

The point is, total cross-section wasn't the only determining factor since the slat had the same cross section in both cases. Vertical height of the slat played a crucial role.

Back to the rebar example: A single 1/2" rebar is thicker, thus "taller" than two 3/8" rebars next to each other. Thus, as per my example, one might imagine that the single 1/2" rebar is more flex resistant than two 3/8" rebars.

None of this really matters too much of course. I'm just wondering "out loud". That's what I do. Sorry.

[Neil2]

Re: 36" in Seattle

End area is all that counts. Structural design usually just stipulates the percentage of the cross section that is to be steel, the size of the individual rebar pieces doesn't matter (with a few exceptions).

Rebar works solely in tension or compression when part of a reinforced concrete structure. It does not resist load through any kind of "flextion" per se, although I understand what you mean.

[kebwi]

Re: 36" in Seattle

Well, I finished digging out and leveling the foundation. This photo doesn't look much different from the earlier photo of the foundation, but it is actually considerably deeper and perfectly bubble level now. I already dumped some gravel in it too. Photos forthcoming.

[kebwi]

Re: 36" in Seattle

First gravel dump. I bought this batch, carefully creaming the large stones off the underlying clay so this is extremely "clear", as they say in the gravel industry (apparently). The rest of the gravel will come from a scrap gravel pile in my yard that was left over from an earlier job (see album photos). It has a high quantity of "fines" in it (gravel colored clay/dust). I think once it's all mixed together it'll make a nice base.

[kebwi]

Re: 36" in Seattle

My ever-evolving hearth-rebar design. In the diagrams the red cores are empty, and thus cannot contain any vertical rebar.

First, if you compare to my earlier designs, you will notice that I beefed up the "weak" corner by converting from a 3-half-block 'L' to a 2x2 half-block column. That space was useless for storage anyway.

The Pompeii directions suggest 1/2" rebar on a 12" spacing. It was subsequently suggested in this thread that 3/8" rebar on a 6" spacing will be functionally equivalent (thanks).

Problem is, it was also suggested that the horizontal rebar be hooked down into the vertical filled cores, and the centers of those cores are on an 8" spacing, not 12" or 6". Instead of stretching it to 16", thus going weaker than any design or recommendation, I went to an 8" spacing (perhaps an alternating mix of 1/2" and 3/8"?). Consequently, only every *other* horizontal rebar can hook into the vertical cores because the remaining horizontal rebars are suspended over empty cores.

Before people suggest that I connect up some of the open corners into long winding rebars, bear in mind that I need to get this stuff home. Thus, I really can't buy anything much longer than 9'-10' without doing something fairly elaborate on my roof rack to prevent the rebar from flopping around. Lashing/taping it to a 12' 2x12 seems like a possibility I suppose.

If you aren't completely drained by the tedium of this discussion, I would appreciate any additional input.

Thanks.

[redmen4]

Re: 36" in Seattle

kebwi,

I was like you in the beginning analyzing and analyzing everything. I read the pompeii plans about 10 times. I finally said to myself that I am not constructing the Empire State Building, in your case the the Space Needle, and just plowed ahead.

My thread is under the Pompeii folder "New Oven in Connecticut"

JQ

[kebwi]

Re: 36" in Seattle

@redmen4: Hmmm...that's some honest advice you've got there.

Truthfully, I'm neck deep in it. I'm just designing the later stages while simultaneously constructing the earlier stages. This week I destroyed a corner of our lawn, leveled the resulting pit, started dumping gravel in it, and have been buying tools and lumber like mad. By the time I have the foundation framed and ready to pour, I'm sure I'll have that rebar all sorted out. Likewise, by the time I dry stack the walls and construct the hearth form, I'm sure I'll have *that* rebar all sorted out too. :-)

Thanks, though. I see your point.

Cheers!

[Neil2]

Re: 36" in Seattle

"I went to an 8" spacing (perhaps an alternating mix of 1/2" and 3/8"?)."

Or if going all 3/8 in, just double up on every second one.

Should do it. Just hook or bend (4 to 6 inches) the dead ends horizontally ( the way you show some of them then over the lintels) and your plan looks fine.

[kebwi]

Re: 36" in Seattle

Thanks Neil2. You're high degree of participation and information-rich feedback have been very helpful.

Now, I just need to some pipe for bending rebar. Home Depot should have that for sure.

[kebwi]

Re: 36" in Seattle

The gravel is done, about three inches deep, a mix of "new" 5/8-minus and a leftover gravel pile in our yard from an earlier job (see album or earlier post for photos).

The first photo shows how the building will work, a four block wide opening on the left side, a five block opening on the right, and a 2x2 super strong column in the weak corner. I went to all the trouble of laying down the first course like this to make sure the foundation will be big enough. Looks pretty.

The second photo shows my growing stockpile of materials. I have many more blocks than are shown because they are scattered around the yard for various purposes, e.g., the first photo and a few other tasks. I'm particularly proud of the (as yet incomplete) pile of 1/2" 20' rebars, which I only got home by pipe-bending them in the Home Depot parking lot to get them on top of my car. At 160 pounds I barely have the leverage to do it without vices or clamps or any other assistance (which would obviously make it cinch).

[Neil2]

Re: 36" in Seattle

Are you pouring the slab with an "apron" slab in front of the wall ? If so, do it in two pours with construction joint or it will crack in this vicinity.