Effects of changes in cross-sectional dimensions of pipe trusses on their internal forces

A tube truss refers to a lattice structure formed by connecting round rods at both ends. Compared to conventional steel trusses with open cross-sections, the cross-section material of a tube truss structure is more evenly distributed around the neutral axis, so the cross-section has good compressive and flexural strength. This kind of steel structure does not use gusset plates, has a simple structure, is easy to produce and install, and has good stability.

For space triangular steel pipe truss, the section shape can be determined after determining the section height, upper chord width and inter-section length. As the width of the upper chord changes, the internal forces in the chord remain essentially the same, but the deflections of the web members and spans will change significantly. The increase in the upper chord width causes a corresponding increase in the inclination angle of the vertical web members. The axial force of the vertical web members continues to increase, and the force transmitted to the vertical web members on the horizontal plane also increases.
At the same time, the increase in the axial force of the vertical web members also leads to an increase in the shear deformation of the members, which is reflected in the increase in the mid-span deflection of the structure. In the case of constant cross-section bending moment, the internal forces of the upper and lower chords will change significantly only when the cross-section height changes. At the same time, as the cross-section height increases, the axial force performance of the web rod decreases due to the decrease in inclination angle. Small and continue to decrease, due to the reduction of bending and shear deformation, the deflection at mid-span also gradually becomes smaller.

Section height is a very important factor that will affect the selection of components, especially the selection of chords, and its impact on structural stiffness is much greater than other factors. The length of the internode will directly result in the angle change between the web members. After changing the length of the internode, the internal force of the chord bar will change slightly, and the axial force of the web bar will change accordingly.
As the length of the internode increases, the inclination angle of the vertical web increases accordingly, so the axial force on the vertical web continues to increase, and the force transmitted to the vertical web on the horizontal plane also increases. The mid-span deflection decreases with increasing internode length and eventually stabilizes. It can be seen from this that if the web members are arranged too densely, it will not play a positive role in the stiffness of the structure. Instead, it will increase the mid-span deflection. The length of the internodes is not necessarily the bigger the better. In order to ensure that the web members and chord members To ensure the reliability of the connection, the general inclination angle is controlled between 35° and 55°.