The document discusses space frames, which are lightweight truss-like structures constructed from interlocking struts in a geometric pattern. Space frames span large areas with few interior supports by transmitting loads through tension and compression along struts. They were developed in the early 1900s and came into wider use in the 1950s. Space frames are used for roofs, floors, and other structures requiring large clear spans. They offer advantages of light weight, prefabrication allowing low-cost construction, and versatility of shapes. Double-layer grids provide increased stiffness over single-layer designs.