The Unistrut System was originally invented in the U.S. in 1955 using one type of node and the same length member for the entire spatial structure. This results in only one geometric form with limited spanning capacity. Unistrut module sizes were 4 ft and 5 ft used for roof systems with total spans ranging between 40 ft to 60 ft. It was later renamed as the “Moduspan System”.

The Unistrut system is made of five components:

1. The in-strut connectors, made from ¼ in. thick steel plate．
2. The out-strut connectors similar to the in-strut connector except that the shear lugs on the four inclined planes are punched outwardly. These connectors are used one for the top and another for the bottom layer.
3. The strut used interchangeably for the webs and chords of the spatial structure made of 0.105 in. thick cold-formed steel in channel-shape with typical sizes of 1.625 in. wide by 1.625 in. or 2.5 in. deep. To connect the members, holes are punched near the ends in order to bolt them to flat or pressed connection plates.
4. The bolts made of high-strength steel with a screw thread diameter of ½ in. and shoulder diameter of 5/8 in..
5. The steel nut for 1/2 in. bolt which had a counter-bored hole of 5/8 in. diameter.

 

These components are field-assembled using power impact wrenches. The sequence for Unistrut System assembly is as follows: The bolt is first put through the hole in the strut and then through the corresponding hole in the connector and then the nut is installed. The nut, with the counterbored hole facing the bolt, is then tightened to draw the parts together. The minimum torque is 50ft-lb. As the bolt and nut are tightened, the shear lugs on the connector automatically engage their matching holes in the strut thus forming a very strong joint. The Unistrut system self-aligns and self-levels. It assembles at a rate of about 16 square feet in 40 minutes, using a crew of 4 men equipped with wrenches.

The Unistrut System can be erected using the cantilever method or lift-slab method or the combination of these techniques. The Unistrut System can not be used to create curved structures such as barrel vaults or domes.

In addition to the basic system (system 1) for which the members are made of channels, Unistrut developed Systems 2 to 6, which use square and circular tubes with spherical nodes (similar to Mero System) in steel and aluminum.