In this paper, under the condition of bidirectional stress, the buckling deformation of the side plate in a rectangular concrete-filled steel tube (CFST) column has been studied in detail. We have conducted a theocratical analysis, an experimental validation and a finite element simulation to investigate the influences of the height-width ratios and Nominal Poisson’s ratios on the buckling form of the side plate, and we also try to explain the change of buckling form between unidirectional and bidirectional stress, both of them can provide a good reference and basis for design and application of the CFST column. The specific work can be summarized as follows: Firstly, a theoretical analysis has been conducted to study the buckling coefficient solution method of the thin plate under the conditions of axial compress and transverse tension. Then, under the conditions of the unidirectional and the bidirectional stress, a comparative study is carried out to investigate the changing relationship of the buckling coefficient (k) of the side plate; the results indicate that the buckling characteristic is changed due to the bidirectional stress, meanwhile, the buckling coefficient and the number of buckling half-wave will increase. Furthermore, the existing outcomes and the numerical simulations are adopted to study the relevance between the number of the elastic buckling half-wave in the side plate and the corresponding height-width ratio of the component; the results indicate that the former is larger than the latter. Finally, based on the obtained, the buckling relationship curve, the conclusion can be drawn as follows: when the bidirectional stress has been applied to the side plate, there is an equal interval between the different buckling half-waves; meanwhile, the interval shows a quadratic function reduce trend with the increase of nominal Poisson’s ratio.

Axial compression tests were conducted on short rhombic tubes of different cross-sectional shapes. The deformation modes of the rhombic short tubes were obtained. To induce a finite element model with deformation modes consistent with the actual working conditions, buckling modes are introduced into the model as the initial imperfections of the structure. However, the buckling modes resulting from finite element buckling analyses often do not meet the needs of actual crushing modes. A coefficient superposition method of solution is proposed to derive modal characteristics consistent with the actual deformation modes by linear superposition of the buckling modes. Through the study of three aspects of theory, test, and simulation, and the comparison and verification of this method with the simulation results of related literature, the results show that the indexes derived from this method are closer to the actual circumstances and are more expandable, which provides a reference for the project.

The corner element is the most basic constitutive element of multi-cellular thin-walled structures; however, scenarios for using relevant theories are limited. To improve this situation, this research investigated the effect of boundary conditions on the compression performance of corner elements with different angles. The deformation laws of corner elements were also explored. The approach was based on experiments and the finite element method. The result shows the outwardly extending plates on both sides yield first, the central twisted wire region then destabilizes and exits the working state, and the plate enters the post-buckling phase. A more relaxed boundary and larger angle can make it easier for the corner elements to trigger the symmetric deformation mode. Moreover, a mechanical model for simplified computation is proposed to predict the initial peak crushing force. The research can provide a reference for studying the compression performance of energy-absorbing elements in engineering.

Weld cracking is a predominant damage mode in tubular connections. Such welds tend to crack prematurely before reaching their ultimate load-bearing capacity, and the damage mode of cracked joints differs significantly from that of seamless ones. This study focuses on the deformation behavior of K-joints with weld cracking at the root of the tension branch. The mechanical properties of the joints under various conditions were analyzed based on experimental observations, load–displacement curves, strain responses, and surface temperature distributions of specimens. Moreover, comparisons were made between the deformation behaviors of joints with and without cracks, and finite element analysis (FEA) was employed for corresponding validation. The main conclusions are as follows: Weld cracking significantly affects joint stiffness and remarkably alters the joint damage mode. Reinforcement plates can effectively strengthen members with cracked welds; however, this reinforcement enhances the stiffness of the tension branch region, thereby altering the force transmission mechanism of the joints. This research offers theoretical and experimental insights for the engineering application of K-joint structures.