Trusses are used in the design of iron bridges and gymnasium girders. Linear materials are slender and light, and can span a large span when combined. Although each linear material is slender, it will become a very solid structure after forming a truss, which can be said to be an incredible structure. The external structure of the "Bird's Nest" is mainly composed of a huge portal steel frame and 24 truss columns.
Conventional truss is a rigid structure composed of geometrically invariant triangular elements, and the members mainly bear axial tension and compression, so the structural efficiency is very high. Truss structure is almost omnipotent to the cantilever and span theme of space structure. The height-span ratio of trusses is generally: space truss112-1/6, three-dimensional arch 1/20- 1/30, and tensed three-dimensional arch1/30. When choosing the truss form, the purpose, material, support mode and construction conditions of the truss should be considered comprehensively.