Rebar placement in a monolithic dome

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Rebar placement in a monolithic dome

Postby RayL Jr. » Wed Apr 06, 2011 10:44 am

I was wondering if one could place rebar "geodesically" as seen at my website - http://rayljraz.tripod.com/

Have spreadsheets for marking rebar in OpenOffice (can convert to Excel). Willing to share for free if anyone's interested for doing different size domes.
This is a unique approach and could be more time consuming, especially for the "1st go round".
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Re: Rebar placement in a monolithic dome

Postby DBS » Thu Apr 07, 2011 4:28 pm

Dear Domaphiles.


For concrete domes, the code is very clear that we need to align the steel with the principle stresses. Those stresses are in the hoop direction and vertical in the radial direction.

I do not know if that is the answer you wanted. DBS
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Re: Rebar placement in a monolithic dome

Postby RayL Jr. » Sat Apr 09, 2011 12:30 pm

I understand DBS. This is not meant for for existing dome projects (or even those planned), as the actual engineering has not been tested nor approved.

I was thinking a new and unique approach, as the 4 courses of rebar do deal with vertical and horizontal stresses like in a geodesic dome. Also considered in a spreadsheet is the sizes of the triangles for rebar on center spans regarding dome size (and dome frequency which relates to number of triangles in the dome) along with concrete thickness. This also was meant to pass in the most extreme seismic zones. There are 4 courses of rebar instead of 2, and the triangle shape does have advantages over square. I was going to start with a project for an experimental doghouse but have put it off due to time restraint issues... I guess the stresses could also be tested in CAD, which I do not currently have the resources for.


A while back I suggested a geodesic wire form for holding the outside of the Crenosphere under inflation to help with airform stresses. I have a letter from you I saved a while back (from the 1990's). These are the only instances where I would use any geodesics, otherwise Monolithic Domes rule. ;)
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Re: Rebar placement in a monolithic dome

Postby eric » Mon Apr 11, 2011 12:09 am

Seem like a geodesic framework for a MD dome would require much more labor than rings and vertical stripes.
Last edited by eric on Fri Apr 22, 2011 10:37 pm, edited 1 time in total.
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Re: Rebar placement in a monolithic dome

Postby rafterman » Mon Apr 11, 2011 9:18 pm

I would like to review your spreadsheet, run some numbers and make some models.

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Re: Rebar placement in a monolithic dome

Postby Gary of CA » Thu Apr 14, 2011 6:18 am

Are you suggesting placing the rebar like on a lattice (cage) mast of a U.S. WW I battleship? Click on the link below for an image of a battleship with lattice cage mast.

http://en.wikipedia.org/wiki/File:Uss_south_carolina_bb.jpg
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Re: Rebar placement in a monolithic dome

Postby Umtallguy » Thu Apr 14, 2011 11:21 pm

seems to be needlessly complicating things. Rebar is cheap insurance.
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Re: Rebar placement in a monolithic dome

Postby RayL Jr. » Sun Apr 17, 2011 7:37 am

Gary, I don't think it really resembles a lattice cage mast, maybe partially. The shape is much stronger, being a dome - not a long tapered mast.
The concept is similar with "horizontal hoops" and 2 diagonal vertical criss-crossings (the fourth course is also vertical). The 4th picture down
in this link - http://www.dieselpunks.org/profiles/blogs/lattice-masts shows the method sort of (but not the shape). To quote "The masts are
a type of hyperboloid structure", as shown in this link - http://www.dieselpunks.org/profiles/blo ... -oka-river

Also the geodesic shape can be made elliptical, either oblong or oblate.

Umtallguy, yes it's definately more complicated. But the smaller lower frequency domes are not that complicated. Modeling/building one would
first start smaller to become more familiar with the process.

rafterman, I sent you a PM.
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Re: Rebar placement in a monolithic dome

Postby Mcfish » Sun Apr 17, 2011 10:14 am

Are there any advantages to your design? Normally a new design uses less material, is easier to build, or is simpler. Maybe it is stronger? Why do we need stronger than current MD designs, if not cheaper or easier?

I'm not sure of the definition of "geodesic" This looks to be "of infinite curvature", i.e. a true dome. Not just a series of triangles or rectangles attached to each other in a quasi-round format. By any definition or argument I have heard, a dome is better than the "geodesic" ? That seems to be what you are stating. Then, why try to complicate the structure?
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Re: Rebar placement in a monolithic dome

Postby RayL Jr. » Thu Apr 28, 2011 2:52 am

Sorry I took a while to answer Mcfish. The dome is better than the geodesic, especially in the case when the geodesic is made of inferior
materials like wood. Also I think the more rounded a geodesic dome is (ergo the higher the frequency) the better it is. Here's an
interesting discussion between "round" and geodesic - http://www.trip.net/~bobwb/ts/synergeti ... tion4.html Buckminster
Fuller is saying a dome and "geodesic" are basically the same thing.

I don't mean to complicate things, just to emulate them. ;)
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Re: Rebar placement in a monolithic dome

Postby jon paton » Wed Dec 21, 2011 10:26 pm

On the Crenosphere
I have looked at the proposed design of the crenosphere, and I’m excited by the concept.
Crenosphere3.jpg
Crenosphere3.jpg (72.61 KiB) Viewed 2601 times
However, that’s just what I see, “concept”.
The analog that is shown is the “Pantheon”
220px-Pantheon_cupola.jpg
220px-Pantheon_cupola.jpg (15.04 KiB) Viewed 2601 times

with the signature global trapezoid vaults. This worked just fine for the Pantheon with an interior diameter of 43.3 meters (142 ft). The Pantheon is over engineered by the standards of today’s MD’s. I propose a different analog for the crenosphere; the golf ball.
golf ball.jpg
golf ball.jpg (3.45 KiB) Viewed 2601 times

Golf balls have round dimples arranged in a tight symmetrical pattern that create micro turbulence and lift. The dimpled ball flies much farther than a smooth ball. With the crenosphere we’re not trying to create lift, however, we’re still using the same geometry for the purpose of breaking the large smooth surface into manageable smaller surfaces that give the small radius of curvature. Instead of dimples on a golf ball we want round augments on the air form, the “crenoform”. Golf companies spend a lot on designing the patterns and sizes of dimples. It’s simple; more dimples in a symmetric pattern mean longer straighter golf shots.
The pattern and size of the augments on the crenoform require the same attention to detail. Perhaps a golf ball engineer should be consulted for designing the crenoform. The cable-stays won’t be put directly on the crenoform. Instead each augment will have a cage built around it, and the cable stay will be attached to the augment cages. This is complicated stuff, but that’s what it’s going to take to build the crenosphere.
The augments will have to be standardized so the rebar for the augments can be prefabricated. The main rebar spans will be larger than normal. Time will be a critical factor during construction. You will need multiple crews working simultaneously for each phase of construction. I would consider sewing loops the crenoform at critical points, like where the cage goes on the top and where the rebar attaches underneath.
A proof of concept will have to be built before a major franchise would buy it.
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Re: Rebar placement in a monolithic dome

Postby DBS » Thu Dec 22, 2011 1:59 pm

To All:
I love the fact that all of you are looking. I would want you to know that we have made innovations from the work of others. But. some of the good ideas cover one problem and double the problem in another area. Nevertheless. Keep at it. Working together we will come up with some fantastic answers.
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