To investigate the bearing behavior of symmetrical full-scale different strength concrete filled double skin steel tube (CFDST) stub columns, 19 full-scale specimens were designed, considering the slenderness ratio (λ); the compression strength of core concrete and sandwich concrete (f_cki, f_cko), the thickness of the inner and outer steel tubes (t_i, t_o); the diameter of inner and outer steel tubes (D_i, D_o); and the tensile strength of the inner and outer steel tubes (f_yki, f_yko) as the main parameters. Nonlinear constitutive models for concrete considering constraint effect were adopted, and a finite element (FE) model was established using ABAQUS software. By comparing the results between simulations and experiments, the rationality of the modeling method was verified. Based on the FE model, the parameter analysis for CFDST columns were conducted, and the force mechanism, stress distribution, and deformation process were analyzed. The results showed that the axial compression bearing capacity ($N_{\mathrm{s}}^{\mathrm{u}}$) increased significantly with an increase in f_cki, t_o, D_o, and f_cko, while $N_{\mathrm{s}}^{\mathrm{u}}$ decreased gradually with an increase in λ. Finally, according to the calculated results of the specimens, the calculation formula for $N_{\mathrm{s}}^{\mathrm{u}}$ of full-scale composite columns was statistically regressed using 1stOpt software and showed a good agreement with the FE.

In order to acquire the hysteretic behavior of the asymmetrical composite joints with concrete-filled steel tube (CFST) columns and unequal high steel beams, 36 full-scale composite joints were designed, and the CFST hoop coefficient (ξ), axial compression ratio (n₀), concrete cube compressive strength (f_cuk), steel tube strength (f_yk), beam, and column section size were taken as the main control parameters. Based on nonlinear constitutive models of concrete and the double broken-line stress-hardening constitutive model of steel, and by introducing the symmetric contact element and multi-point constraint (MPC), reduced-scale composite joints were simulated by ABAQUS software. By comparing with the test curves, the rationality of the modeling method was verified. The influence of various parameters on the seismic performance of the full-scale asymmetrical composite joints was investigated. The results show that with the increasing of f_cuk, the peak load (P_max) and ductility of the specimens gradually increased. With the increasing of n₀, the P_max of the specimens gradually increases firstly and then gradually decreases after reaching a peak point. The composite joints have good energy dissipation capacity and the characteristic of stiffness degradation. The oblique struts force mechanism in the full-scale asymmetrical composite joint domain is proposed. By introducing influence coefficients (${\xi }_1$ and ${\xi }_2$), the expression of shear bearing capacity of composite joints is obtained by statistical regression, which can provide theoretical support for the seismic design of asymmetrical composite joints.

Honeycombed beams are widely used because they are conducive to the layout of pipelines and circuits, and the traditional honeycombed beams are generally H-shaped steel beams and concrete-encased upper flange composite beams. In this paper, a composite beam with concrete-filled steel tube as both upper and lower flanges and steel plate with circular openings as web is proposed. The effective constraint of steel tube on concrete strengthens the deformation ability of concrete. In order to study the flexural behavior of composite beams with concrete filled steel tube flanges and honeycombed steel webs (SHC), 25 simply-supported SHC beams were designed to carry out the four-point bending load simulation analysis. By reasonable modeling method. The main parameters of SHC concluding the compression strength of concrete (f_ck), yield strength of steel (f_yfk), height-to-span ratio (H/L), ratio of space to height of web (s/h_w), thickness of steel tube flange (t₁), thickness of web (t₂) and ratio of hole to height of web (a/h_w) were discussed, and the whole loading process of the beam was analyzed. The results showed that the SHC specimens could be divided into elastic stage, elastic-plastic stage and plastic stage under four-point bending load. Steel tube in the tensile zone yielded firstly before specimens failed, and the failure mode of the specimens was that the concrete at the loading point was crushed. Though the steel tube in lower flange at the support, loading point and mid-span yielded, the web did not buckle. SHC could meet the requirements of Chinese code in the normal use stage, and the cross-section deformation basically conformed to the plane assumption. Finally, based on the unified strength theory, a prediction formula of ultimate bending moment is established, which is in good agreement with experiment and can lay the foundation for the popularization and application of this kind of beams.