Numerical Study on the Mechanical Properties of Transmission Tower K-Joints under Cyclic Loading

During the vibration of a transmission tower, the joints will be subjected to a reciprocating load. To obtain the accurate state of the transmission tower under the load, the mechanical properties of the joints under the vibration load must be considered. In this paper, the mechanical properties of typical K-joints in transmission tower structures are studied by numerical simulation. The failure mode of the K-joint under cyclic loading is also analyzed. The mechanical properties of the K-joint are discussed from the aspects of hysteretic characteristics, stiffness degradation, energy dissipation capacity, and ductility evaluation, and the influencing factors are discussed. The results show that the failure mode of the K-joint is related to the bolt grade and steel strength. When analyzing K-joints, the moment-rotation hysteresis curve should be combined with the realistic parameters of joints to consider the hysteretic behavior of the K-joint. The results provide a theoretical reference for the accurate modeling of transmission towers.

Seismic Behavior of a Novel Buckling-Restrained Steel Plate Shear Wall

In this study, in a novel buckling-restrained steel plate shear wall (BRSPSW) with out-of-plane deformation spaces, angle steel stiffeners have been installed so as to create gaps between the steel plate and the covering concrete slabs. A finite element model has been developed to analyse the effect of the gap. According to the finite element results, seismic performance of this novel BRSPSW has been tested under cyclic loading at the scale ratio of 1/3. The failure pattern, hysteretic characteristics, skeleton curve, equivalent stiffness, ductility, and energy dissipation have all been systematically analysed. A stiffened steel plate shear wall (SPSW) has also been tested in order to determine the differences between these two steel shear walls in load-carrying capability and the function and significance of the gap. The test results show that the novel BRSPSW does not only significantly enhance the ultimate bearing capacity, stiffness, ductility, and accumulated energy dissipation of the SPSW but also keep the steel plate basically intact at the end of the test. This can be attributed to the existence of the gaps between the infilled steel plate and the covering concrete slabs. The hysteretic characteristics and the strength and deformation characteristics of this novel BRSPSW have been simulated by using the finite element model, and the test results are in good agreement with the finite element results. Hence, the BRSPSW is an excellent steel plate shear wall to be used in high rise structure to resist horizontal loadings.

A Comprehensive Study on the Optimal Design of Magnetorheological Dampers for Improved Damping Capacity and Dynamical Adjustability

Purpose: We aim to provide a systematic methodology for the optimal design of MRD for improved damping capacity and dynamical adjustability in performing its damping function. Methods: A modified Bingham model is employed to model and simulate the MRD considering the MR fluid’s compressibility. The parameters that describe the structure of MRD and the property of the fluid are systematically examined for their contributions to the damping capacity and dynamically adjustability. A response surface method is employed to optimize the damping force and dynamically adjustable coefficient for a more practical setting related to the parameters. Results: The simulation system effectively shows the hysteretic characteristics of MRDs and shows our common sense understanding that the damping gap width and yoke diameter have significant effects on the damping characteristics of MRD. By taking a typical MRD device setup, optimal design shows an increase of the damping force by 33% and an increase of the dynamically adjustable coefficient by 17%. It is also shown that the methodology is applicable to other types of MDR devices. Conclusion: The compressibility of MR fluid is one of the main reasons for the hysteretic characteristics of MRD. The proposed simulation and optimization methods can effectively improve the MRD’s damping performance in the design stage.

Comparison of Hysteresis Models for Nonlinear Dynamic Analysis of Structural Systems

Hysteresis is a non-linear phenomenon exhibited by the mechanical systems. Beyond elastic limit the loading and unloading path of most of the system will differ and that nonlinear path is indicated by hysteresis. The reason for shape of hysteretic cure may due to either changes in material properties beyond the elastic range or due to the changes in structural geometry because of subjected load. This response is a function of both immediate deformation and the previous residual deformation acted on it since it represents the dissipated energy of structure. The hysteretic characteristics or degrading characteristics includes pinching, stiffness degradation, load deterioration, and sliding. A study of four commonly available hysteresis models, which are Bouc Wen Model, Mostaghel Model, Menegotto Pinto Model and Preisach Model were briefly reviewed and discussed in this section and the outcome of this study is the best fitted model for the nonlinear analysis. The scope of the work is to simulate nonlinear response of the building frame subjected to earthquake excitation in a most effective way.

A Sliding Mode Controller Using an LS-SVM Model for a Water-Hydraulic Artificial Rubber Muscle

We describe a sliding mode controller design for an artificial rubber muscle driven by tap-water pressure. The hysteretic characteristics of this water-hydraulic artificial rubber muscle (WARM) often deteriorate its control accuracy. To cope with this complicated hysteresis, a modeling approach based on the least squares support vector machine (LS-SVM) with nonlinear kernel functions is first applied to a WARM. By employing this LS-SVM-based WARM model, a sliding mode controller is then derived for the WARM drive system. We verify the control performance of the proposed controller and compare its tracking accuracy with our previously developed controller through experiments.

Suppression of Complex Hysteretic Resonances in Varying Compliance Vibration of a Ball Bearing

It is traditionally considered that, due to the Hertzian contact force-deformation relationship, the stiffness of rolling bearings has stiffening characteristics, and gradually researchers find that the supporting characteristics of the system may stiffen, soften, and even coexist from them. The resonant hysteresis affects the stability and safety of the system, and its jumping effect can make an impact on the system. However, the ball bearing contains many nonlinearities such as the Hertzian contact between the rolling elements and raceways, bearing clearance, and time-varying compliances (VC), leading great difficulties to clarify the dynamical mechanism of resonant hysteresis of the system. With the aid of the harmonic balance and alternating frequency/time domain (HB-AFT) method and Floquet theory, this paper will investigate the hysteretic characteristics of the Hertzian contact resonances of a ball bearing system under VC excitations. Moreover, the linearized dynamic bearing stiffness of the system will be presented for assessing the locations of VC resonances, and the nonlinear characteristics of bearing stiffness will also be discussed in depth. Our analysis indicates that the system possesses many types of VC resonances such as the primary, internal, superharmonic, and even combination resonances, and the evolutions of these resonances are presented. Finally, the suppression of resonances and hysteresis of the system will be proposed by adjusting the bearing clearance.

A Modified Fractional Maxwell Numerical Model for Constitutive Equation of Mn-Cu Damping Alloy

To better describe its constitutive relation, we need a new constitutive equation for an important nonlinear elastic material, Mn-Cu damping alloy. In this work, we studied the nonlinear and hysteretic characteristics of the stress-strain curve of the M2052 alloy with the uniaxial cyclic tensile test with constant strain rate. The strain rate and amplitude correlations of M2052 resembled those of nonlinear viscoelastic material. Therefore, we created a new constitutive equation for the M2052 damping alloy by modifying the fractional Maxwell model, and we used the genetic algorithm to carry out numerical fitting with MATLAB. By comparing with the experimental data, we confirmed that the new constitutive equation could accurately depict the nonlinear constitutive relation and hysteretic property of the damping alloy. Taken together, this new constitutive equation for Mn-Cu damping alloy based on the fractional Maxwell model can serve as an effective tool for further studies of the constitutive relation of the Mn-Cu damping alloys.

Exponential Functions for Modelling Hysteresis of Soil-Water Characteristic Curves

Soil – water characteristic curve (SWCC) is an important property of unsaturated soils that can be used to estimate various parameters to describe unsaturated soil behavior. SWCC is reported to be hysteretic because the water content at a given suction in the wetting process is less than that in the drying process. In order to simulate the hysteretic characteristics of SWCC, many models have been proposed by different researchers. However, majority of the existing models are complex and their parameters are not related to the physical significances of SWCC variables. In this study, the new equations are developed to model drying and wetting SWCC. In addition, some indexes are proposed to estimate the wetting SWCC from drying SWCC. The new equations for SWCCs were evaluated with the laboratory data from published literatures. The results showed that the proposed equations performed well in modelling drying and wetting SWCC. The new equation has less parameters than the existing published equation.