Truss is a widely used structure of the rod system. Fig. 7 and Fig. 8 are truss structure bridges. The so-called truss is that each rod in the structure of the rod system is a side of the geometric simplex in the structure, for the plane truss, the simplex is the triangle, each pole is at least one side of the triangle, for space truss, simplex is tetrahedron, each pole is at least a tetrahedron's edge. So if each rod of the truss is treated as a rigid body, the rod system they form will not deform and is very sturdy.
Truss (Héng) frame (Jià): A structure formed by a hinge connected to each other at both ends. The truss is composed of a straight bar generally has a triangular unit of plane or spatial structure, the truss rod is mainly subjected to axial tension or pressure, which can make full use of the strength of the material, in the larger span than the real abdominal beam to save material, reduce weight and increase stiffness.
The advantage of Truss is that the rod is mainly subjected to tensile force or pressure, which can give full play to the material, save material and lighten the weight of structure. Commonly used are steel truss, reinforced concrete truss, prestressed concrete truss, wood truss, steel and wood composite truss, steel and concrete composite truss.
Trusses are commonly used in steel trusses, reinforced concrete trusses, prestressed concrete trusses, wood trusses, steel and wood composite trusses, steel and concrete composite trusses. The truss is divided into triangular truss, trapezoidal truss, polygonal truss, parallel chord truss and hollow truss. In the selection of truss form, the use, materials, supporting methods and construction conditions of trusses should be considered, and the materials and the amount of labor used in the manufacture and installation should be minimized.
1, Fixed truss: the strongest of the truss, can be reused, the only drawback is higher transport costs. Products are divided into square tube and round pipe two kinds.
2, Folding Truss: The greatest advantage is the low cost of transportation, can be reused less. Products are divided into square tube and round pipe two kinds.
3, Butterfly Truss: The most artistic one in the truss, peculiar shape, beautiful.
4, the ball section Truss: Also called the ball section frame, the modelling is graceful, the solidity is good, is also the truss cost highest one kind.
Sufficient strength-no fracture or plastic deformation, rigid enough-no large elastic deformation, sufficient stability-no sudden change in the form of equilibrium resulting in collapse; good kinetic properties-seismic and wind resistance. Truss design requirements: To have the required bar, to have good connectors, including rivets, pins and weld connection. These relate to the type of truss, the size of the rod and the material, but the first is static mechanics analysis.
The truss node of engineering is usually a certain rigid node rather than an ideal articulated joint, and the bending stress and axial stress of the rod are called secondary stress due to the influence of the rigidity of the joints. In order to calculate the secondary stress, the axial deformation of the rod should be considered, which can be solved by the method of statically indeterminate structure or finite element method.
The space truss is composed of several planar trusses, which can be decomposed into the plane truss of the same plane of the truss and calculated by the finite element method.
According to the material used in the truss and the internal force of the calculation, the proper section should be used to ensure the overall stiffness and stability of the truss and the strength and local stability of each member to meet the requirements.
The overall stiffness of the truss is guaranteed by controlling the maximum vertical deflection of the truss without exceeding the allowable deflection. The support system consists of a winding support, a chord support, a vertical support and a truss space stabilization system.