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Spreadsheet for a 2v diameter wire/rebar dome
Spreadsheet for a 4v diameter wire/rebar dome
Spreadsheet/chart for wire and rebar gauges

Spreadsheet specifications

Here are descriptions and specifications outlined for the spreadsheets that cover 2v, and subsequently 4v wire/rebar dome assembly

The spreadsheet plans for marking and cutting wire for your desired geodesic dome diameter are not that complicated once you know what the main inputs and some other parameters are... The descriptions of parameters below also corrsepond to the 2v geodesic dome diagram, which should be referred to as so not to get too confused. The key to understanding this is to go over it one step at a time and keep reviewing, it should then become much more familar to you and much easier to comprehend. Remember - practice makes perfect!

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Main input parameters:

* First all input parameters are highlighted in blue, the yellow highlights are the main output parameters that are worth consideration. Since it's ALOT easier to calculate and measure out the wire in metric for precision, everthing will be done in metric - with only the English measurements or input parameters used as a reference. The actual spreadsheet refers to the metric input parameters... The numbers are read out in meters to 5 decimals and accurate to .01 millimeters (or 1/2,500th of an inch)

* There's the input radius, which is specified at 1' in radius or 2' in diameter. This radius will be exactly what the 4 courses radii (or "radiuses") will be when averaged, also called the Rebar centerline radius.

* The wire used is 12 gauge wire or 2.05 mm in thickness for Course 1 & 4 wire/rebar and Course 2 & 3 wire/rebar wire diameters.

* Inputs for rows 4-7 or "Concrete thickness" to "Inside cover (min)" are ignored (as "Concrete thickness" is set to zero)... Minimum wire/rebar overlap is where the 4 courses are overlapped and tied - they are calculated at 40x wire diameter. Rebar overlap length is the length used in the calculations (length makes the overlapping twist ties (or rebar built to code) more secure...).

* Rebar base extension and Course 1-4 overlap “spacers” are used as shown in the illustrated picture. Base extension is just that, so wire can be bent and secured around bottom of the dome. Course 1-4 overlap “spacers” are short wire segments used at the top of the dome, where the pentagon sides have to be directly overlapping for the wire to tie in.

Now that the main input parameters have been specified, we can go about on how the wire is actually measured and cut! _________________________________________________________________________________________________

Measuring the wire for bending, marking and cutting...

Now for the main 4 courses in which the whole dome is laid out:

From right to left, in columns 1-8 are the main 4 courses that make up the whole dome. Course 1 being the outermost, Courses 2 & 3 being the middle diagonal courses and Course 4 being the innermost or "inside vertical course".

Course 1: Going down the 1st column, you'll see the numbered arc segments (they are numbered in corresponding order in the illustration). Column 1 (horizontal segments) shows from top to bottom 2, o1-oe1-1-lp1, and 2-2.

The 1st arc segment labeled "2" is simply the part that also would correspond with "normal" hub and strut placement. The 2nd arc segment is o1-oe1-1-lp1. The "o" in "o1" stands for overlap, being that segment extends to overlap through it's corresponding "pentagonal side" to the right. This is the same metric measurement as "Rebar overlap length derived from the input cells"... The section "oe1" means "overlap extension" for Course 1 from the left side pentagon intersection, and "lp1" extents the segement to end at the left side (on the next pentagon at left).

Going down the 2nd column is where the measurements are simply made. For example o1-oe1-1-lp1 is the length of wire that's marked and measured accordingly, and the last lp1" is where the wire is cut...

Courses 2 & 3: Going down the 3rd, 4th, 5th and 6th columns the rows and letters/numbers for Courses 2 & 3 correspond as in columns 1 & 2 for Course 1, but the letters as in b2-2-2-o2 differ slightly. Course 2 & 3 are actually "identical", only the radius is slightly different so they can "directly overlap". The "b" in "b2" stands for base extension, and as you see from the spreadsheet is the same measurement as "Rebar base extension" (which also is same as the "Rebar overlap length"). The "o" on "o2" is the same reference as the overlap that's used in Course 1, except the overlap is the end segment that will "tie in" with Course 1 on the corresponding pentagonal side.

Also note that all arc segments for Course 2 & 3 are laid out from left to right, this makes assembly a lot more orderly and to easy to lay out and tie over cardboard form...

Course 4: Course 4 is the course that helps tie the whole dome together, especially at the top of the dome... There are 4 repeating segments: tp1-1-oe1-o1, and 1 segment o1-oe1-1-1-oe1-o1 that runs an "overlap" for the others to sit on when tied. "tp1" stands for top pentagon and "oe1" stands for overlap extension that runs "through" the corresponding pentagon.

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Now each of these sections are repeated 5x apiece for marking and cutting, so for each course numbered 1, 2, 3 and 4 there are 5 segments to repeat. These are more easily marked and cut in groups of 5 on the main circular wire form or jig...

If you'll notice in the spreadsheet under columns 2, 4, 6 and 8 - each sequence of segments and their listed numbers are "staggered" on the text or aligned to the middle and right sides. This is so once cut, the segments can be marked with tape or labels named Course 1a, Course 1b, Course 1c and Course 2a Course 2b, etc...

To get a better understanding of what's going on here just see this top dome illustration. For Course 4, if we have arc segment tp1-1-oe1-o1, this will be labled in a set of 4 (not 5 in this case) named Course 4a and each section will be as named - tp1, 1, oe1, o1 and so on... Now that the 4 main courses have been explained, we can go finally to the "Top pentagon 5-way overlap" and other sections in the lower right hand side of the spreadsheet!

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Overlapping segments and placement in the dome:

Top pentagon 5-way overlap: Here you'll also see a "Course 0" has been added, this is simply a top course for the top of the dome to be tied in (sort of an exception to the 4 courses rule, though Couse 0 is the only exception, there's no "6th course"). The measurements to the right are the same as used correspondingly with courses 1-4. Again the top dome illustration will show exactly how these are tied in...

* "Overlap extension length/course" is the course that lets all 5 Course 4 sements tie in.
* "Course 4: 2 overlaps + extension" and "Course 4: overlap + extension" also help tie in Course 4 to the top dome pentagon. The lengths stated to the right (in meters) means there are 1 of each to be marked and cut.
* "Course 4 overlap, # of & length" and "Course 1-4 spacers, # of & length" are also measured in meters. For example "Course 4 overlap, # of & length" reads .13208 meters (or 13.208 centimeters) and the number 6 just to the right means there are 6 segments to be measured and cut for placement. The same goes for "Course 1-4 spacers, # of & length", which are needed to properly space and align the other overlapping courses.
* The "-mark" symbol denotes where to mark the mid-pentagon on the corresponding pentagon wire for Course 1 so to align the top pentagon overlap connections...

Now for the next section below:

5 mid-pentagons 2-way overlap: This has the overlap segment for Course 1 which overlaps the other Course 1 in corresponding pentagon to the right in diagram. "Course 0: 2 overlaps + extension" means this segment goes over Course 1 to tie in both Courses that could not otherwise be joined (a custom "coupler" or "connector" would be necessary). Also if you note for Course 1,2,3,4 arc sections of the arc segments "oe" deotes "overlap extension" as mentioned here...

And for the final section:

10 lower hexagons 2-way overlap: These are where the overlap segments go to tie in with Course 1 at bottom of dome. "Course 1 overlap, # of & length" denotes the overlap length of .13208 meters and there are 20 of them. For each tie in at bottom of dome section (below top 5 main pentagons), there are 2 overlap segments used to reinforce connecting segments of Course 1.

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There you have it! The net total rebar needed to make this dome from the calculations is 125.03261 feet or 38.10994 meters. In case you wonder how accurtae these calculations are, they've been cross-verified out to 13 decimal places past 0, or about .0000000000001 meters (1/10 trillionth of a meter)