Characterized in that chords are used to replace the flanges and webs, and the webs and chords are connected with each other by welding or other connection methods through joint plates (or other parts). Sometimes, members can be directly welded (or otherwise connected) to each other without gussets. In this way, the bending moment of the plane truss as a whole is represented by the compression and tension of the upper and lower chord axes, and the shear force is represented by the compression or tension of the web axis.
Trusses are widely used in steel structures, such as roofs (roof trusses). ) and crane beams (crane trusses), bridges and cranes (their towers, beams or suspenders, etc.) of industrial and civil buildings. ), hydraulic gates and offshore oil platforms, steel trusses are often used as the main components of load-bearing structures. All kinds of steel grid structures widely used in roof structures of long-span public buildings belong to space steel trusses. Various types of towers, such as TV, power transmission, drilling, tower crane and mast tower, usually use space steel trusses composed of three, four or more plane trusses.
Compared with solid web beams, steel trusses use sparse web members instead of full web members, and members mainly bear axial force, which can often save steel and reduce structural weight. This makes steel truss especially suitable for structures with large span or height. In addition, steel trusses can be made into various shapes according to different requirements. In addition, because the amount of steel used in the web member is less than the web of the solid web beam, the steel truss can usually be made to have a greater height and thus greater rigidity. However, the steel truss has many members, many joints, complex structure and labor-consuming manufacture.
Among steel trusses, simply supported beam trusses are the most commonly used. Due to the definite stress of this truss, the internal force of the member is not affected by the settlement and temperature change of the support, and the structure is simple and the installation is convenient; But the amount of steel used is slightly larger. Although rigid frame and multi-span continuous steel truss can save steel, their internal forces are sensitive to bearing settlement and temperature change, and their manufacturing and installation accuracy is high, so they are rarely used. In the steel frame of a single-story factory building, the steel truss of the roof often forms a single-span or multi-span rigid frame with steel columns, which has high horizontal stiffness and can better meet the requirements of large cranes or vibration loads. Continuous steel trusses are often used in structures such as long-span bridges and mast tower structures with fiber cables. Arch steel trusses are often used in long-span public buildings and bridges. Cantilever steel trusses are often used in offshore platforms and some building structures. All kinds of towers belong to cantilever structure.
Steel trusses can be divided into ordinary steel trusses, heavy steel trusses and light steel trusses according to the internal force, section and joint structure characteristics of members. Ordinary steel trusses generally adopt single web members, which are usually T-shaped sections composed of two angle steels, and sometimes cross-shaped, grooved or tubular sections. The joints are connected by gusset plates, which is simple in structure and the most widely used. The members of heavy-duty steel truss are under great stress. They adopt H-shaped or box-shaped sections composed of steel plates or sections, and the joints are connected by two parallel joint plates. It is often used for steel trusses with large span and heavy load, such as bridges and long-span roof trusses. Light steel truss is made of small angle steel and round steel, or cold-formed thin-walled steel. Nodes can be connected through joint plates or directly through members. It is mainly used for roofing structures with small span and light roof.