With the development of China’s modernization construction and rapid scale expansion of industrial and mining enterprises, the application of trestles of steel structure becomes wider and wider, and it proportion in the trestle structure becomes wider and wider, too. Especially for the trestles with height > 15m~20m, due to their characteristics of low construction cost and fast construction speed, the structure types of trestles of steel structure become more and more and are gradually developing toward the direction of large, high and heavy structure. However, with the continuous increase of the span, height and weight of steel structure trestle, the installation becomes more and more difficult. The installation can be carried out smoothly only through careful design. Only in this way can the further optimization and continuous innovation of structure type of large-span steel structure trestle be promoted.
The truss is the unchanged geometric body made of rod elements, which can be used as independent structure and can also be used as a unit of the structure system to play the load-bearing role. The scope of engineering to which the truss of broad sense corresponds is very wide, for example, simply supported or continuously supported vertical truss can be used for bridges and roof truss, horizontally placed truss can be used for the crane brake system in the industrial workshop, wall surface wind-resistant bearing and belt conveyor corridor, and transmission tower, microwave tower, latticed column, etc. adopt vertical cantilever truss. 
    Rod elements constituting the steel truss can be the section of the steel tube, e.g., round, rectangular or square steel tube, rolled I-beam, H- or T-steel, angle steel or section of combination of double angle steel; in some light gauge trusses, round steel can also be used as the tension rod element. A truss can be composed of rod elements formed by different sections.
    Usually, there are 3 types of truss, i.e., triangular truss, trapezoid truss and parallel chord truss. The triangular truss is usually used for the roof with relatively big slope; trapezoid truss is widely used for such structures as roof truss and bridge truss, etc.; while the parallel chord truss is mostly used for bridge truss, bracket and wind-resistant truss in workshop.