Steel T-Bar Connector
The introduction to geodesic dome building. Light gauge steel T-bar (drywall)
ceiling grid geodesic frame. Rigid foam insulation, waterproof stucco exterior and your choice of finished
interiors. The low cost housing in any shape. Ideal for a garage, storage
shed, barn or small home. The material cost starts at $1.00 per square foot.
These are #10 X 5/8" Pancake head self-drilling screws. The self-Tapping (drilling ) screws are the needed to
screw threw the heavy steel connector. The simplest and least expensive connector for this T-bar geodesic structure comes from the Electrical Supply House for contractors. These are called Reducer Washers. For the inside connection I prefer the 3" outside diameter X 1/2" inside diameter center hole. For the outside connector I use a larger Reducer Washer, 4" outside dia. with a 3" center hole. The larger reducer washer is needed on the outside connection of the structure to allow for the 18 degree angles at the ends of the T-bar struts. The 3" center hole allows the reducer washer to lie flatter on the outside surface. This structure can be built without these connectors and other self-tapping screws can be used.
An extra pair of hands is always nice to have. When using your self drilling screws you must have the steel clamped tightly together. Vise-grip pliers or C-clamps, any self-locking pliers will work. A pair of tin snips (metal cutting scissors) is needed to cut the light gauge T-bar steel. A
cordless drill with a magnetic Philips head screw tip works well for this project, but any drill motor with a screw tip will work. Any tape measure over 12' will be needed for your layout and cutting struts.
The Drywall T-bar ceiling grid can be purchased at the local drywall supply store. It comes in boxes of 4' cross T's and 12' main T's. This is also your source for 1-1/2" x 1-1/2" wall angle for the bottom foundation D struts, rigid foam insulation, exterior synthetic stucco, screws and tools. Once you know the diameter of the geodesic structure you will be building and have calculated the lengths with the cord lengths you can optimize the materials that will work best for your dome
structure. These geodesic structures were designed to range under 30' in diameter or 900 square feet using these products. There are 250 struts which 20 of these will be angle for the foundation row.
In this connection system the T-bar struts need to meet in the center of the connector on the inside of the structure only. The sides need to over lap each other so you can connect the two T-bar struts and the connector together with a screw. You will have to cut the corner off at least one side of the T-bar struts to get the center points to meet.
If you have any spherical design, engineering or building code questions please send us an e-mail and we will try to reply as quickly as possible. firstname.lastname@example.org
Spherical Geodesic Structures prefers using the 4V (frequency) Icosahedrons
geometry to create dome structures. Unlike the 3V the 4V has a horizontal flat line (great circle) at the hemisphere. This makes your foundation connection easier using the geodesic triangles. The 4V uses smaller triangles than the 3V to create the same size dome structure.
With shorter strut members and smaller triangles optimizing materials is greatly
enhanced using the higher frequency geodesic geometry. As the geodesic structure increase in diameter over 40' this makes a stronger geodesic structure and also makes the components easier and safer to handle by one person during construction.
We need some way of checking our 18 degree connections and strut angle during construction. My method for this is to use one of the 4' T's and cut the back side 2' from the ends so it will bend to a total of 18 degrees. Take one of the inside reducer washers and screw it in place over the cut out area on your T to hold it from moving. Once you have
screwed your washer in place double check your new template to see if it is holding at 18 degrees.
Now during construction, once you have screwed the inside strut and connector in place you can clamp your new jig to the inside of your strut face to face to hold it in place while you screw your outside reducer washer in place. Once your outside reducer washer is connected your strut should hold itself at your 18 degree angle. It never hurts to have another pair of eye's double
checking the construction diagram. This is the fun part of the puzzle. Some of the struts are close in length and you may not recognize you have made a mistake until you get to the other side and things are not going together as easy as before. This connection system is very forgiving and the light weight materials make this spherical geodesic structure a great inexpensive project to start your geodesic dome building adventures.