Light Gauge Steel Connection
Cold formed steel members are used for studs, joists, rafters and headers. It is zinc coated (galvanized) to prevent corrosion. Steel framing provides excellent design flexibility due to the inherent strength of steel. Light gauge steel has been used for many years in commercial structures and recently has become more common in residential construction. Many shapes are available, but the primary shapes are the C-shape stud and the U-shaped track. Framing members are generally produced in thickness of 12 to 25 gauges with 3-1/2" to 12" widths.
SIMPSON STRONG TIE have been producing engineered connectors and strapping for over 40 years. Every structure built uses some kind of Simpson product. These are the only connectors and straps the engineering and building department will accept. All hardware stores carry Simpson products and will order any connector or strapping from their catalog.
# GT6Z is the ID number for the Gazebo Connectors. Listed under Home Project connectors in the SIMPSON catalog. This are designed for 6-sided (hexagon) roof trusses. A case of 8 connectors cost under $50. Simpson makes many different straps. # MSTA24Z is what is used here. The number 24 stands for the length in inches and for dome building 18" to 24" works well.
The light gauge steel studs for your spherical geodesic structures will be 16 and 18 gauge. The connectors and strapping will also be 16 to 18 gauge. The engineering standard are # 10 screws. It is a must to use self tapping screws. This is a screw with a self drilling tip. My preference is the pancake head or flat head screws 5/8" long. I found some at Home Depot but you may have to go to the drywall supply store.
All spherical geodesic structures are designed to be built by one person. To screw two pieces of steel together they need to be clamped together. Locking adjustable C-clamps are a must when building with steel. They come in two sizes 6" and 4" with or without round feet on the ends. These are your extra hands and for safety you need them. Cordless drills work well for steel framing because they spin slow and don't burn up the screw tip.
The 6" stud gives you the minimum insulation space for the nation building code standard of R-19 using fiberglass bat materials. Most commercial structures built in steel studs use 3 1/2" rigid foam on the exterior to achieve R-19 or better, so the use of 3 5/8" steel stud walls are acceptable. You have cut all your struts to length with something close to 9 degrees on the ends and measuring from the long sides to get your proper cord length (strut length).
Screw your steel strapping to your Simpson Gazebo connector. 2 screws in each strap in the center of your connector. I suggest you put the screws in from the outside of your connector so the tips don't get in the way of your plywood later. You can bend your 9 degree angle on all six ends of the connector and strap. The steel stud slides in between the connector and the strap.
The stud will stop at the recess in the connector and also this is were your screws connected the connector and strap. All your struts should stop close to the same place all around the connector for each strut. The strap will be on the inside of the steel stud and the connector on the outside of the stud. No straps are needed on the connectors for the inside of the hub.
Diagonal bracing is required on all structures. On box shaped structures you must have a diagonal brace every 12 feet of wall and from every corner. This is the national building code. This is why we see plywood used a great deal on the outside of wood structures and especially two-story structures. Were the building codes are enforced with inspections, the nailing is inspected on the plywood shear panels and roof sheathing. Spherical geodesic structures are all diagonals so they don't need the shear panels or diagonal braces. The plywood is most important to the structural integrity of the geodesic structure.
The connection from one triangle to the next relies on end nailing or screwing. OSB or particle board should NEVER be used for exterior sheathing on a geodesic structure. The edges have no
structural strength and it is very susceptible to moisture damage. Multi-ply wood sheathing is the only acceptable standard for geodesic structures. The bottom two rows should be sheathed first. This is the weakest area on the geodesic structure and any other shaped structure. The lower two rows are usually easy to reach and from there sheathing from the top down is easiest on dome structures. Nails are required every 6" on the outside edges of your plywood. Screws are required every 8". Screws have more holding power than nails and screws are coated and do not rust.
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
There are 6 pentagons you need connectors for and more than 75 hexagons. With the use of your clamps and a hammer you can make adjustments to your gazebo connector and use them for your pentagon connector. All the weight of the dome structure is pushing out on the bottom levels. This is the importance of the strapping. If you wish to not use the straps on the 3rd, 4th and 5th rows that is fine. There is less outward force on the connectors the higher you go up the structure.