Structural classification of building steel trusses
From the perspective of mechanics, the shape of the building steel truss is similar to the bending moment diagram of the simply supported beam. The axial force distribution of the upper and lower rotating rods is relatively uniform, and the axial force of the web axis is small and the amount is saved. If the analysis is made from the material and manufacturing aspects, the wooden truss is made into a triangle, while the steel truss is made of parallel chord or trapezoidal reinforced concrete, and most of the prestressed concrete trusses are trapezoidal and polygonal. The ratio of span to height is usually between 12:1 and 16:1, while the three-dimensional arch is between 20:1 and 30:1.
So far, the application range of truss is quite extensive. When choosing its form, it needs to be considered from many aspects, including the support method, the construction conditions of materials and soil, and the principle of form selection is to meet the requirements of use. Under the premise, the materials and labor required for manufacturing and installation can reach a relatively small level.
Under the nodal load evenly distributed along the span of the triangular truss, the axial force of the upper and lower rotating rods is relatively large at the end points, and will gradually decrease when going to the middle, and the axial force of the web members will be opposite. The axial force at the end is relatively small, and it gradually increases towards the middle. Due to the large difference in internal force of the triangular truss, the material consumption process is often unreasonable. At present, it is mostly used on the roof truss of tile roofs. Compared with the triangular truss, the stress of the trapezoidal truss and the rods has been improved, and it is easier to use it in the roof truss to meet the process requirements of some industrial plants.
If the upper and lower chords of the trapezoidal truss are parallel, it is a parallel chord truss. The stress of the rod is slightly worse than that of the trapezoidal truss, but the type of the belly rod is greatly reduced, which is mostly used in Bridges and trestle.
Polygonal truss is also called polyline truss. The upper chord node is located on the quadratic parabola. If the upper chord is arched, the bending moment caused by the inter-node load can be reduced, but the manufacturing is more complicated. Under the action of uniform load, the shape of the truss is similar to the bending moment pattern of the simply supported beam, so the axial force of the upper and lower chords is evenly distributed, the axial force of the web member is small, and the material is the most economical. It is a truss form commonly used in engineering.
The hollow truss basically takes the shape of a polygonal truss, without sloping web rods, and is only connected by vertical web rods and upper and lower chords. The axial force distribution of the member is similar to that of the polygonal truss, but the bending moment value of the rod end changes greatly under the asymmetric load. The advantage is that there are fewer rods intersecting at the nodes, and the construction and manufacturing are convenient.
After reading the above content, the readers here must have a clear understanding of most of the truss structures on the market. I hope that reading this article can help you.