A structure in which the bars are connected to each other at both ends by means of a hinge. A truss is usually composed of a straight or triangular element. The truss bar is mainly subjected to axial tension or pressure to take full advantage of the strength of the material. When the span is large, it can save material, reduce weight and Increase stiffness.
The definition of a truss: The truss is supported by a bar, which is welded, caulked or bolted.
The advantage of the truss is that the bar is mainly subjected to tension or pressure, can give full play to the role of materials, saving materials, reduce the weight of the structure. Commonly used steel truss, reinforced concrete truss, prestressed concrete truss, wood truss, steel and wood composite truss, steel and concrete composite truss.
Truss is a widely used rod structure. The so-called truss, that is, the rod structure of each pole is a geometric shape of the structure of a side, for the plane truss, simple shape is a triangle, each rod is at least one triangle of a side, for space truss, Simplex is a tetrahedron, each of which is at least one of a tetrahedron. Therefore, if the truss of each pole are regarded as rigid body, they constitute the rod system is not deformed, is very strong.
Since we know that the deformation of the rod is l / 1000, its strain is 1/1000, so the tensile stress is E / 1000, bending stress now more than a primer a / l, and because the cantilever beam at the fixed end is the largest , It can be seen that the bending stress of the rod is one order of magnitude smaller than the tensile stress. Therefore, in analyzing the force of the truss, the bending stress of each rod can be omitted. This is why the node is assumed to be hinged when analyzing the truss.
It is important to note that the assumption that the load is acting on the node is purely for the purpose of analyzing the force without bending the bars. If there is a pole outside the load is added to the middle of the bar, it is also easy to do, first load the equivalent distribution to the adjacent node analysis truss, and then as long as the pole as the actual load and reverse The effect of the beam to analyze the results, and the results obtained with the truss can be superimposed on the results.
The above discussion of the bending of the truss is purely considered from the order of magnitude, since the conditions set are unfavorable and the actual situation is much smaller than the bending stress in the discussion. So the analysis of the truss, you can safely consider only the rod by the tension or pressure on it. However, sometimes it is necessary to carefully discuss the bending of the bar in the truss, for example, in the statically indeterminate structure, some rod deformation is relatively large, has exceeded the proportion of the limit of plastic deformation, or structural deformation requirements more sophisticated , Need to consider the bending caused by the deformation, this time need to consider the truss all the rod bending. The result of this analysis is called the secondary stress of the truss.