Search Results (8)

Whip restraints based on thin-walled structures are widely used for protection against high-energy pipe breaks in nuclear power plants due to their excellent impact resistance. Recently, biomimetic and hierarchical structures have emerged as focal points in thin-walled structure research, aimed at enhancing energy absorption capacities. Drawing inspiration from the nautilus shell and Fibonacci spiral, based on the nautilus bionic hierarchical multi-cell (NBHMC) structure, this study introduces a novel Nautilus Bionic Double Hierarchical Multi-Cell (NBDHMC) structure. Finite element analysis was employed to evaluate the energy absorption performance of the structure under axial and oblique loads using four crashworthiness parameters. Crashworthiness studies showed that the NBDHMC exhibits superior crashworthiness compared to the NBHMC and hollow circular tube configurations. Finally, the study investigated the influence of combination modes, hierarchical levels, cross-sectional characteristics, and other parameters on the parameterization of the NBDHMC. The results offer innovative insights for the design of highly efficient energy absorbers. Full article

Corroded transmission towers, whose load-bearing capacities are lowered, are suffering from wind-induced damage. By simulating the member corrosion through section thinning, the structural dynamic finite element model of an angle-steel transmission tower with a corrosion depth of 0 mm to 1.4 mm was established using ANSYS/LS-DYNA software. The incremental dynamic analysis method was used to study the collapse mode of the tower under different degrees of corrosion, as well as the effects of corrosion on structural self-vibration characteristics, wind-induced member stress, and tower-top displacement. The results show that with the corrosion deepening, the first three vibration frequencies decrease, and the torsional mode becomes the first mode. When the corrosion depth is smaller, the overall structure failure occurs under strong wind. The failure starts at the most unfavorable oblique rod between the upper and middle cross arm, then expands to the rods under the lower cross arm. When the corrosion depth is larger, the overall structure failure occurs restrictedly between the upper and middle cross arm. Internal axial force and bending moment redistribution happen when corrosion deepens. Under the critical failure state, the oblique rods are always at a high stress level, while the stresses of the main rods decrease. Corrosion has a stronger impact on component strength and stability than on structural stiffness. Full article

This study aimed to investigate the axial compression performance of concrete-filled circular-end aluminum tube (RECFAT) columns, utilizing four specimens with varying parameters such as cross-sectional aspect ratio and cross-sectional aluminum content. Axial compression tests and ABAQUS finite element extended parameter analyses were conducted, with key mechanical performance indicators such as specimen failure morphology, ultimate bearing capacity, load–displacement curve, and load–strain curve being obtained. The influence of various variation parameters on the axial compression performance of the specimen was analyzed. The results indicated that the majority of specimens underwent oblique shear failure due to local bulging of the aluminum tube plane, while specimens with an aspect ratio of 4.0 experienced overall instability failure. As the aspect ratio increased, the bearing capacity improvement coefficient and ductility coefficient of the specimen decreased and the initial stiffness of the specimen gradually decreased. As the aluminum content increased, the initial stiffness decreased, with the critical aspect ratio for overall instability being between 2.0 and 2.5. The optimal aluminum content was recommended to be between 8.5% and 13.5%. When the aspect ratio was around 2.0, the lateral strain of the round-ended aluminum tube developed faster and the constraint effect was the best. The finite element model accurately reproduced the oblique shear bulging of the round-ended aluminum tube and the internal concrete V-shaped collapse, with the axial load–displacement curve being in good agreement. Improving the strength of aluminum alloy was more conducive to improving the axial compression bearing capacity of RECFAT than increasing the strength of concrete. A simplified model and calculation method for RECFAT was proposed, with an error of less than 1%. Full article

The design of intersecting nodes in high-rise oblique mesh structures is a critical issue. The existing research on the intersecting nodes of oblique meshes mainly focuses on plane intersecting nodes and monotonic axial compression loads. The plane intersecting nodes cannot consider the contribution of the node’s out-of-plane angle and floor beam to the node’s out-of-plane stiffness in actual structures. In this paper, numerical analysis using ABAQUS was conducted to investigate the mechanical performance of space intersecting nodes of oblique meshes (OMSIN) under cyclic axial tension and compression loads, to provide a reference for the engineering application of oblique mesh structures in seismic regions. Six parameters were considered: the space intersecting angle, the plane angle symmetry coefficient, the plane intersecting angle, the out-of-plane constraint restraint, the steel content of the cross-section, and the concrete strength. The study showed that changes in the thickness of the steel tube wall are unfavourable for the uniform transmission of stress. Increasing the space intersecting angle significantly weakened the seismic performance, and the space angle affects the failure mode of the node. Asymmetric arrangements of the upper and lower plane angles caused nonlinear development of out-of-plane. The ultimate load and overall compressive stiffness of the specimen were positively correlated with the plane angle, and vertical constraints should be applied to the node position of components with plane angles greater than or equal to 70°. The out-of-plane constraint was a key factor affecting the seismic performance of the node, and it was proportional to the ultimate load of the component. In structural design, if the aim is to improve the mechanical performance of the component by increasing the steel content, more enormous out-of-plane constraints should be set to control plane external displacement strictly. The concrete strength is proportional to the ultimate axial load and axial stiffness, and its influence on the mechanical performance in the axial tension direction is not significant. Finally, a dimensionless skeleton curve model of the node was established. The existing formula for the bearing capacity of CFST columns was fitted to obtain the calculation formula for the axial yield and ultimate load of the OMSIN under cyclic loads. Full article

Twenty-five cadaveric adult femora’s anteversion angles were measured to develop a highly efficient and reproducible femoral anteversion measurement method using computed tomography (CT). Digital photography captured the proximal femur’s two reference lines, head-to-neck (H-N) and head-to-greater trochanter (H-G). Six reference lines (A/B in transverse section; C, axial oblique section; D/E, conventional 3D reconstruction; and M, volumetric 3D reconstruction) from CT scans were used. The posterior condylar line was used as a distal femoral reference. As measured with the H-N and H-G lines, the anteversion means were 10.43° and 19.50°, respectively. Gross anteversion measured with the H-G line had less interobserver bias (ICC; H-N = 0.956, H-G = 0.982). The 2D transverse and volumetric 3D CT sections’ B/M lines were consistent with the H-N line (p: B = 0.925, M = 0.122) and the 2D axial oblique section’s C line was consistent with the H-G line (p < 0.1). The D/E lines differed significantly from the actual gross images (p < 0.05). Among several CT scan femoral anteversion measurement methods, the novel anteversion angle measurement method using CT scans’ axial oblique section was approximated with actual gross femoral anteversion angle from the femoral head to the greater trochanter. Full article

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. Full article

In this paper, we propose a method of forming a tube into an oblique/curved shape by synchronous multipass spinning, in which the forming roller reciprocates in the radial direction in synchrony with the rotation angle of the spindle while the roller moves back and forth along the workpiece in the axial direction to gradually deform a blank tube into a target shape. The target oblique/curved shape is expressed as a series of inclined circular cross sections. The contact position of the roller and the workpiece is calculated from the inclination angle, center coordinates, and diameter of the cross sections, considering the geometrical shape of the roller. The blank shape and the target shape are interpolated along normalized tool paths to generate the numerical control command of the roller. By this method, we experimentally formed aluminum tubes into curved shapes with various radii of curvature, and the forming accuracy, thickness distribution, and strain distribution are examined. We verified that the curved shapes with the target radii of curvature can be accurately realized. Full article

Shale reservoir has an initial unloading effect during the natural uplift and erosion process, which causes the shale brittleness to change, affecting the design of the fracturing scheme. To consider this, the axial compression loading and confining pressure unloading experiment of shale is carried out, and then the influence of unloading rate on the mechanical parameters, failure characteristics, and the brittleness of rock are analyzed. What is more, a new evaluation method of brittleness characteristics that take the unloading effect into consideration is proposed. The conclusions are as follows: (1) The unloading rate has a weakening effect on the mechanical parameters, such as the destructive confining pressure and the residual strength of the samples. (2) The failure characteristics of shale specimens are a single shear failure in an oblique section under low unloading rate, and multiple shear zones accompanied with bedding fracture under high unloading rate. (3) The brittleness of shale samples is well verified by the brittleness index $B_{d1}$ and $B_{d2}$ during the loading path; nevertheless, it has shortage at the unloading path. This paper proposes a new brittleness evaluation method which can consider the influence of the different unloading rates and unloading points. Furthermore, there is a nice characterization between the brittleness damage and this method. Full article