Trusses are usually planar or spatial structures composed of straight bars and triangular elements. Under load, truss members mainly bear axial tension or pressure to make full use of the strength of materials. Compared with solid web beams, truss members can save materials, reduce self-weight and increase stiffness when the span is large, so they are suitable for long-span load-bearing structures and towering structures, such as roofs, bridges, transmission line towers, satellite launch towers, hydraulic gates, crane racks and so on.