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The magnetic shielding device, made of high-permeability soft magnetic material, is sensitive to external influences and requires a protective steel enclosure. A steel enclosure, being strongly ferrimagnetic, can alter the surrounding magnetic field distribution, thus impacting the shielding effectiveness. This study proposes a novel analytical approach to quantify this effect, which has not been previously researched. The method develops a simplified finite element simulation model based on the structural symmetry of the steel enclosure. By using this model, this study analyzes the impact of steel structures with varying heights, widths, and remanent magnetization values. The validity of the method is confirmed through experimental tests on steel buildings. The findings offer insights into the optimal placement of magnetic shielding systems and provide theoretical guidance for designing large-scale magnetic shielding devices. [ABSTRACT FROM AUTHOR]

The large-span, relaxed antenna network is a large deformation flexible structure due to its low pre-tension level of the wires. Its dynamic analysis under a wind load belongs to dynamic and geometric nonlinear problems, which is very complex to accurately calculate and solve. This paper explores the possibility of the finite particle method (FPM) to the aeolian vibration analysis of a large-span, low stress-tensioned antenna cable net. In the FPM, the antenna network structure is discretized into a group of finite particles, where the motions of all particles follow Newton's second law and can be solved dynamically using a central difference scheme. The effectiveness and applicability of the FPM were verified by comparing the calculation results of the finite element method and FPM. The FPM was used to study the effects of wind speed and the distribution of vibration on the aeolian vibration of antenna cable nets. The results showed that this method is suitable for studying the aeolian vibration of a large-span, low stress-tensioned antenna network and has high computational efficiency and accuracy. [ABSTRACT FROM AUTHOR]

The residual magnetic field in a magnetic shielding device with a multilayer high permeability material (permalloy) structure can be obtained at the nanotesla (nT) level or even lower. At present, in the process of designing a magnetic shielding device, most of the external environmental magnetic field settings are set at the size of the Earth's environmental magnetic field, but the instruments inside the magnetic shielding device need to be powered, the active compensation coil needs to be powered, and the degaussing coil of passive shielding layer needs to be powered, so substations need to be used around magnetic shielding devices. The magnetic field generated by the substation will affect the magnetic shielding device, so this paper analyzes and measures the magnetic field generated by the substation. Firstly, the finite element model of a substation is established, and the influence of different substations on the environmental magnetic field is analyzed by changing the power. Secondly, the test method of a substation environment magnetic field is determined. Finally, the site test was carried out to measure the influence of different power substations and different distances on the magnetic field, and its influence on the magnetic shielding device was analyzed, which provided an important basis for the construction of the magnetic shielding device. [ABSTRACT FROM AUTHOR]

Fatigue cracks are typical damage of threaded steel rods under dynamic loads. This paper presents a study on ultrasonic guided waves-based, fatigue-crack detection of threaded rods. A threaded rod with given sizes is theoretically simplified as a cylindrical rod. The propagation characteristics of ultrasonic guided waves in the cylindrical rod are investigated by semi-analytical finite element method and the longitudinal L(0, 1) modal ultrasonic guided waves in low frequency band is proposed for damage detection of the rod. Numerical simulation on the propagation of the proposed ultrasonic guided waves in the threaded rod without damage shows that the thread causes echoes of the ultrasonic guided waves. A numerical study on the propagation of the proposed ultrasonic guided waves in the threaded rod with a crack on the intersection of the smooth segment and the threaded segment shows that both linear indexes ( R f and ARS) and nonlinear indexes ( β r e ′ and β ′ ) are able to detect the crack. A constant-amplitude tensile fatigue experiment was conducted on a specimen of the threaded rod to generate fatigue cracks in the specimen. After every 20,000 loading cycles, the specimen was tested by the proposed ultrasonic guided waves and evaluated by the linear indexes and nonlinear indexes. Experimental results show that both the linear and nonlinear indexes of the ultrasonic guided waves are able to identify the crack before it enters the rapid growth stage and the nonlinear indexes detect the crack easier than the linear indexes. [ABSTRACT FROM AUTHOR]

Soil-structure interaction (SSI) is involved in the pile-supported structures. Such effect is mainly accounted for soil-pile interaction (SPI) driven by the deformation of pile and surrounding soil, and thus it can become significantly obvious due to large soil deformation during a severe earthquake. To capture this characteristic of simply supported bridge structure with pile foundations, a three-dimensional (3D) finite element (FE) model is developed using the computational platform OpenSees considering SPI. A two-span reinforced concrete bridge with a single pier located in multi-layered clay is employed as a test-bed. A variety of seismic responses of this coupled soil-pile-bridge system are systematically investigated. Furthermore, a parametric study is performed to explore the influences of SPI, multidirectional excitation and earthquake characteristic on the seismic responses of soil and structure. The results show that: (1) the seismic response of the bridge structure is significantly affected by its longitudinal and transversal different configuration; (2) the fixed-base support type noticeably influences the seismic response of bridge structure and (3) the direction and characteristic of base input earthquake motion greatly influence the seismic response of the bridge-soil system. [ABSTRACT FROM AUTHOR]

Abstract: A new form of space structure, polyhedron frames, was developed recently. In polyhedron frame structures, most structural members are under multi-loads of compression, bending and torsion. A new type of tapered member that is obtained by axially connecting a constant-section tube to two tapered and relatively short tubes was proposed to be the structural member of polyhedron frame structures. We named this kind of tapered member a tapered-end tube. This paper has analytically and experimentally proved that tapered-end tubes can restrict the plastic hinge to the interface of the constant-section part and the tapered part, and the location of the plastic hinge can be arranged by correctly choosing the ratio of slope of the tapered ends. Corresponding tests and simulations are done to verify the analytical prediction, and these also reveal that the strength of the tubes is significantly improved by the tapered ends. [Copyright &y& Elsevier]

Reconstruction, according to physical shape, is a novel way to generate free-form grid truss structures. 3D scanning is an effective means of acquiring physical form information and it generates dense point clouds on surfaces of objects. However, generating grid truss structures from point clouds is still a challenge. Based on the advancing front technique (AFT) which is widely used in Finite Element Method (FEM), a scheme for generating grid truss structures from 3D scanned point clouds is proposed in this paper. Based on the characteristics of point cloud data, the search box is adopted to reduce the search space in grid generating. A front advancing procedure suit for point clouds is established. Delaunay method and Laplacian method are used to improve the quality of the generated grids, and an adjustment strategy that locates grid nodes at appointed places is proposed. Several examples of generating grid truss structures from 3D scanned point clouds of seashells are carried out to verify the proposed scheme. Physical models of the grid truss structures generated in the examples are manufactured by 3D print, which solidifies the feasibility of the scheme. [ABSTRACT FROM AUTHOR]

The cable-strut structures have the features of low stiffness and weak damping, resulting in large vibration response under dynamic excitation. The vibration response of the cable-strut structures can be reduced by active control methods. However, many traditional active control methods need to build a state-space model (SSM) based on finite element model (FEM), and solving the active control force for the high-dimensional SSM is time-consuming. In this paper, the dynamic mode decomposition with control (DMDc) method is proposed to achieve a data-driven reduced-order SSM for active vibration control of cable-strut structures. This proposed method only uses the data of structural response and control force input to build reduced-order SSM and does not rely on the FEM. Linear quadratic regulator (LQR) design using the DMDc-based reduced-order SSM (DMDc-LQR) is more computationally efficient than that using the FEM-based SSM (FEM-LQR). The relationship between the design parameters of the DMDc-LQR controller and the FEM-LQR controller is established, which ensures that the control performance indexes of the DMDc-LQR controller and the FEM-LQR controller are equal. The effectiveness of the proposed DMDc-LQR method is validated using numerical Kiewitt cable dome and tensegrity grid under wind and seismic loads. The results show that the DMDc-LQR controller maintains similar control effect to that of the FEM-LQR controller and has advantage of high computing efficiency as well. In addition, the influence of critical parameters (i.e., data noise and model order) on vibration control effect is comprehensively explored. It is found that increasing the model order is effective to mitigate the noise influence on the DMDc-based reduced-order SSM and ensures the effectiveness of the DMDc-LQR controller. • A data-driven reduced-order state-space model (SSM) method is proposed. • The linear quadratic regulator (LQR) is designed based on reduced-order SSM. • The control effect and design efficiency of two LQR controllers are discussed. • The influence of noise and model order on the vibration control effect is explored. [ABSTRACT FROM AUTHOR]

Welded hollow spherical joints are one of the most popular joints used in reticulated shell structures. Welded hollow spherical joints in service may need to be strengthened due to age-related damage or unexpected overloading. Adding external stiffeners to the welded hollow spherical joint is an effective way to strengthen it. In this paper, experimental and numerical studies are performed to investigate the enhanced behavior of welded hollow spherical joint with external stiffeners. Axial compression tests of five specimens are performed with a particular focus on the effects of the number, height, and thickness of the external stiffeners on the load-bearing capacity of the joint. A 3D finite element model is developed and calibrated against the experimental results. Parametric studies on a number of design variables are conducted using the calibrated finite element model. The results show that the external stiffeners significantly enhanced the compressive capacity of the joint, and the compressive capacity of the joint is increasing with the number, height, and thickness of the external stiffeners increasing. It is also found that the diameter of the hollow sphere has little impact on the enhanced behavior of the welded hollow spherical joint with external stiffeners. Practical formulas for axial load-bearing capacity and initial axial stiffness of the welded hollow sphere joint with external stiffeners are developed, based on the results of parametric studies. Comparison of enhancement coefficients of load-bearing capacity determined by experiments, numerical simulations and proposed formula. [Display omitted] • Few researches on the mechanical properties of welded hollow spherical joints (WHSJs) with external stiffeners. • The failure mode of WHSJs with external stiffeners was obtained through axial compression tests with five specimens. • Numerical study on the effects of different parameters on the compressive behavior of WHSJs with external stiffeners. • The formulas for calculating the load-bearing capacity and initial axial stiffness of WHSJs with external stiffeners. [ABSTRACT FROM AUTHOR]