Buckling Modes of Cold-Formed Thin-Walled Panels for Prefab Houses

There are three basic buckling modes for cold-formed thin-walled strips of movable slab houses: local buckling, distortional buckling, and global bending-torsional buckling of members. Ideally, all three types of buckling belong to the stable bifurcation instability problem diagram, but the buckling wavelength and post-buckling performance are different.

(a) Local buckling

(b) Distortion buckling

(c) Global flexural-torsional buckling

The first is local buckling buckling. The buckling stress is related to the half-wave length formed during buckling, and the half-wave length is related to the bending stiffness of the plate, the stress distribution of the section and the boundary conditions of the edge. The half-wave length of local buckling is short, and many uneven bands are often formed in the component. After buckling, the connecting line between the plate and the plate remains the original straight line, so the profile shape of the component section remains unchanged. After buckling, the strength of the flexible and thin plate is greatly improved, and the geometric defects of the plate have little effect on it.

The second is the distortional buckling of the section, or buckling. When the movable prefab room is buckling, rotation occurs at the connection of the compression plate parts, which causes the adjacent plate parts to be displaced, thus changing the original cross-sectional shape and outline size. The distortional buckling stress of the section is related to the length of the half-wave formed. The distortional buckling stress is also related to the flexural stiffness, torsional stiffness, buckling stiffness, stress distribution of the section, and boundary conditions of the compression flange. The half-wave length of distortional buckling is moderate, fewer bands are formed in the component, the magnitude of strength increase after buckling is small, and geometric defects have a greater impact on it.

The third type is the global buckling of the member. Including flexural buckling, torsional buckling and flexural-torsional buckling, the half-wave length of the member during buckling is the longest, which is related to the force and boundary conditions. The strength does not increase significantly after buckling, and the influence of geometric defects is obvious.

In the prefab house project, when the span of the channel steel and the Z-shaped wiper is 4-6m, 1-2 lateral ties are generally set, and when it exceeds 6m, two and Above the side straps. Therefore, it is generally believed that the lateral support of the wiper member can be guaranteed by the structure, therefore, the overall bending-torsional buckling of the wiper strip is not studied in detail in this paper. The displacements of local buckling and distortional buckling both occur at the compression flange. The local buckling point and distortional buckling point in the figure are respectively the upper flange is uniformly compressed, the web is subjected to pure bending and the L-roll is non-uniformly compressed. The fiber compressive stress at the edge of the section is the sign of the local and distortional minimum buckling stress. As shown, the distortional buckling stress is significantly lower than the local buckling stress. The overall bending-torsional buckling point in the figure represents the bending-torsional buckling stress of the member. At this time, the section has only lateral and torsional displacement, but the shape of the section does not change. Due to the structural requirements of the strip in engineering, the strip can be sufficiently laterally restrained without lateral instability. Therefore, when studying the performance of cold-formed thin-wall strip members, researchers are often more concerned about The local buckling and distortional buckling properties of the wiper strip, and the lateral stability of the wiper strip are guaranteed by the structural requirements.

It has been shown that the post-buckling strength of distortional buckling is smaller than that of local buckling, so for some sections originally thought to be controlled by local buckling, the final buckling mode may be distortional buckling trapped. . Therefore, further research on distortion buckling is of great significance for accurately guiding engineering practice.

Because the cold-formed thin-walled member of the prefab house is mainly used as an intermediate member between the main frame member and the roof or wall, it is widely used in various buildings. It will have a certain impact on cold-formed thin-walled strips. For cladding systems such as roof panels, due to the different rigidity of the white body, the degree of influence on the wiper is also different. At the same time, the stress conditions of cladding systems such as roof panels are often complex, and the distortion buckling considered in existing codes, such as the Eurocode, cannot be applied to calculate the shaving edges affected by cladding.