[Domesteading 00464] Re: Rebar dome

J & D Goldman jmgoldma at dwx.com
Mon Nov 2 19:55:39 PST 2009

  My initial interest in rebar was partly due to the fact that it
seemed ignored (or overlooked?) by almost all of the dome information
I've reviewed over the years.  Sometimes territory like that leads to
discovery, although sometimes after the exploration one discovers
nothing of any value.  Just didn't know which way it would go with
this one.

  Yes, for starters, I was thinking about this primarily for smaller
sheds, utility buildings, maybe garage, etc. and not as much for
larger structures or dwellings.  For one thing, rebar is sometimes
available as scrap, and once again, domes can be built of short pieces
of waste that are unsuitable for use in more traditional structures.

The hook idea occurred to me as well. Once bent to the axial angle,
these could be joined as struts and fastened at any given face angle.
This does confer a certain simplicity (think "Simplicity Domes" from
discussions in the past) to construction by eliminating "the hub" as a
separate structual component. A hub can be a real speed bump for
domes, especially if one gets into ellipicals or some dome that
requires more than 2 or 3 hubs.  Rebar lends itself to this building
approach better many other common and inexpensive materials.  It is
also lends itself to disassembly and reassembly better than some
others as well.  In a pinch, some of the hook bends could be adjusted
to allow pieces to be reused, but there might be some strength-loss
issues if that is overplayed.  I built a model of this out of tie-wire
and it was quite stable.  I may try one from 3/8 and see how it goes
together and holds up.  Sure, it could be welded, and actually some of
the newer adhesives that are being used to replace rivets might work
well also if the rust isn't an issue, although I was thinking of some
other ways of joining the "axial hubs" so they could be dissembled if
desired. I was thinking of coating the rebar with some of that
elastomer they use on roofing to see if it would stick and "soften up"
the surface to be more compatible with materials like clear poly - for
a small greenhouse.

If there are more ideas out there, I'd be interesting in hearing them.
If I use Rustoleum, I'll be thinking of Sal's spindles...

cheers - Dan G.

-----Original Message-----
From: Sal Cerda <sal.cerda at rocketmail.com>
To: off-the-grid livingA forum for the discussion of aspects of
independent <domesteading at sculptors.com>
Date: Monday, November 02, 2009 9:37 AM
Subject: [Domesteading 00463] Re: Rebar dome

>I like the way you are trying to think out of the box.  Yet, I still
don't know why the idea of a rebar dome is appealing to you.  What
properties of the rebar do you like aside that you can carry a lot
more of it?
>For a dwelling, you still have to cover it with something. Your
discussion of the smoothness implies some thought to the covering.
>For a hub and strut dome, you will have to find a way to connect the
individual struts to the hub. Clamps?  Why not just weld the rebar and
be done with it? Maybe you could create a custom bending jig and
create hooks on the end or just an angle then clamp or wire them
together while you weld.
>I cut hundreds of rebar spindles for my railing on the second level
loft in my dome. I used a 'chop saw' with a metal-cutting abrasive
blade. I painted them black with Rustoleum and inserted them into 1/2"
holes in a top and bottom rail.  PRESTO - beautiful 'wrought' iron
railing with fancy texture on the spindles.
>So, you can see that I have nothing against rebar, but I still don't
know why you'd want a dome with rebar struts unless you plan to use it
for it's major structural benefit - tensional strength in concrete.
There will be a lot of compression acting on the lower struts and they
might bend under all the weight.  Of course I'm thinking of a larger
dome and you may be thinking of a smaller one which would not have all
that weight to it. 'Dimpling' would be less of a problem with smaller
domes with very short rebar struts.
>--- On Sun, 11/1/09, J & D Goldman <jmgoldma at dwx.com> wrote:
>> From: J & D Goldman <jmgoldma at dwx.com>
>> Subject: [Domesteading 00462] Re: Rebar dome
>> To: "A forum for the discussion of aspects of independent,
off-the-grid living" <domesteading at sculptors.com>
>> Date: Sunday, November 1, 2009, 8:27 PM
>> Thanks, Sal and Bob, for your
>> comments. I wasn't really considering
>> rebar for its more routine use as a framework support for
>> concrete
>> domes. I was thinking about applying the use of it
>> for other types.
>> So here are a few thoughts to share.
>> As to disadvantages of rebar over conduit, I can think of a
>> few.
>> - Doesn't have the excellent galvanize and corrosion
>> resistance of
>> conduit. Rebar rusts just sitting in the open and needs to
>> be coated
>> if that's an issue.
>> - Conduit has a pretty smooth surface, suitable for tarp
>> covers and
>> other tearable/scratchable surfaces. Although you *can* get
>> smooth
>> rebar, the more common stuff is deliberately *not* smooth
>> as it is
>> designed to prevent sliding inside concrete. This
>> rough outer texture
>> is actually the subject of industry standards for
>> manufacture, not
>> just a random thing.
>> - Rebar likely cannot handle as much load as a piece of
>> tubing unless
>> used in an engineered structure. Its designed to
>> provide tensile
>> strength (resist stretching, which is how it strengthens
>> concrete.)
>> Now, as to some possible advantages:
>> - Yes, rebar bends (to make shapes or maybe when one would
>> rather it
>> didn't), but can be bent back. There are limits to that, of
>> course,
>> but aside from extremes, straightened rebar may not be
>> pretty or
>> perfectly straight, but if you overload a tube and it
>> creases, its
>> done-for and usually cannot be restored.
>> - Weight and price, one can argue they are often about the
>> same
>> actually (unless you get into the big stuff), depending on
>> what's on
>> sale or what is available from surplus or salvage. However,
>> a load of
>> 3/8 rebar will actually take up less space than equivalent
>> lengths of
>> 1/2 inch conduit. That could be a factor where one is
>> loading a
>> trailer and wants to maximize what they can load, as long
>> as the
>> weight limit is not an issue.
>>  - Cutting is an issue. Conduit, usually cut with a
>> saw, cutoff wheel
>> or perhaps tubing cutter (clamp-rotational type with smooth
>> blade. )
>> However, a large bolt cutter works really well with 3/8,
>> 1/2 and even
>> 5/8 rebar, and then there are rebar cutter/bender machines
>> that use a
>> shear. So if you want to cut a lot of pieces really
>> fast, especially
>> if you in the back country without a lot of power (or no
>> power), I can
>> see some situations where cutting rebar may be
>> easier/faster than
>> cutting conduit.
>> - Fastening - both are somewhat similar if done with straps
>> or clamps,
>> although conduit is probably easier to punch or drill
>> through if you
>> want holes. However, rebar ends won't crush or
>> deform, being a hard
>> dense material. I also wondered if one could actually
>> staple rebar
>> with the right equipment.
>> I've been looking at ways to use rebar as a frame for
>> hub/strut and
>> panelized domes that normally use pipe, tubing or wood for
>> support. I
>> do see some traps, but I also see some possible
>> advantages. If anyone
>> has thoughts or experience about this, I'd be interested to
>> hear them.
>> I really have not seen much of this discussed in any of the
>> dome books
>> or information I've reviewed in the last few years.
>> That may be
>> because its a bad idea, or also, perhaps, it *looks* like
>> its a bad
>> idea but...
>> - Dan G.
>> -----Original Message-----
>> From: Sal Cerda <sal.cerda at rocketmail.com>
>> To: off-the-grid livingA forum for the discussion of
>> aspects of
>> independent <domesteading at sculptors.com>
>> Date: Tuesday, October 20, 2009 6:41 AM
>> Subject: [Domesteading 00460] Re: Rebar dome
>> >As strong as it is, rebar can be bent rather
>> easily. What would be
>> the benefit of a rebar dome? I am supposing that
>> there would be some
>> benefit over a metal conduit dome. It sure would be
>> heavier though.
>> >
>> >--- On Mon, 10/19/09, RoConroy at aol.com
>> <RoConroy at aol.com>
>> wrote:
>> >
>> >> From: RoConroy at aol.com
>> <RoConroy at aol.com>
>> >> Subject: [Domesteading 00459] Re: Rebar dome
>> >> To: domesteading at sculptors.com
>> >> Date: Monday, October 19, 2009, 10:08 PM
>> >>
>> >> In a message dated 10/19/2009 7:41:39 P.M. Central
>> Daylight
>> >> Time,
>> >> jmgoldma at dwx.com
>> >> writes:
>> >>
>> >> Have any of you done, seen or heard of domes
>> being
>> >> made from rebar
>> >> frames? I know rebar can be used in concrete
>> >> domes in various ways,
>> >> but I was thinking mroe in terms of a hub and
>> strut
>> >> or panel type
>> >> unit. For a while the steel prices really dropped
>> and
>> >> rebar was really
>> >> inexpensive. I had a few ideas but wondering if
>> >> I'm merely
>> >> reinventing the wheel...
>> >>
>> >>
>> >>
>> >> Dan,
>> >> I built a lightweight concrete
>> >> dome which used a perlite-cement mix
>> >> sprayed over a rebar frame which was covered with
>> 6x6
>> >> steel mesh.
>> >> Actually, to increase solar gain, I used a half
>> dome
>> >> on the north with an open arch
>> >> structure on the south. The problem being that
>> >> the light weight concrete
>> >> had about the same insulating value as fiber
>> >> glass. With 4 inches of
>> >> concrete you really don't have sufficient
>> insulation
>> >> to make the structure
>> >> energy efficient, except that it has zero
>> >> infiltration, and a lot of thermal
>> >> mass. The equipment needed to spray the
>> >> concrete was too expensive, and I
>> >> find that high tech insulation incorporated into
>> pre
>> >> built wooden panel dome
>> >> is much easier and cheaper, unless you are looking
>> to
>> >> cover the dome with
>> >> earth to prepare for the Mayan year 2012.
>> >> Bo
>> >>
>> >
>> >
>> >
>> >

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