This paper investigates damping ratio in micro-beam resonators based on magneto-thermo-elasticity. A unique aspect of the present study is the effect of permanent magnetic field on the stiffness and thermo-elastic damping of the micro resonators. In our modeling the theory of thermo-elasticity with interacting of an externally applied permanent magnetic field is taken into account. Combined theoretical and numerical studies investigate the permanent magnetic field effect on the damping ratio in clamped-clamped and cantilever micro-beams. Furthermore, the influence of the magnetic field intensity on the frequency of the micro-beams with thermo-elastic damping effect is evaluated. Such evaluations are used to determine the influence of magnetic field on the vibration amplitude of the resonators. The meaningful conclusion is that the magnetic field increases the equivalent stiffness and thermo-elastic damping and consequently the energy consumption of the resonators.

A series of shaking table tests were performed on reduced-scale models of helical soil-nailed walls (HSNWs) to evaluate the effect of the nail arrangement and nail inclination on the failure mechanisms and dynamic characteristics of the retaining structures under seismic conditions. The results of particle image velocimetry (PIV) showed that the potential failure surfaces in the helical soil-nailed walls was a parabolic one with an inflection point and the dimensions of failure wedge increased as the length and inclination of the nails increased. A combination of overturning and base sliding was identified as the predominant deformation mode in the HSNWs and that base sliding faded with an increase in the nail inclination. It was found that horizontal helical nails located in the lower half of the wall played a more effective role in reducing lateral displacement, but the opposite was true for HSNWs with inclined nails. The use of inclined nails instead of horizontal ones was found to be an efficient solution for increasing the shear modulus in HSNWs. The efficiency of this solution decreased with the use of shorter nails in the upper half of the walls and was eventually minimized by increasing the length of the nails across the wall height. It was found that, although the use of helical nails instead of grouted ones reduced wall damping, it could be a good solution for increasing the stiffness of the soil-nailed walls.

Identification of damping properties for a mixed structure and its interaction with underlying soil is a challenge for structural designers. Current codes and available commercial software packages do not provide analytical solutions for such structural systems. Due to irregular damping ratios, dynamic response of each part of a mixed structure differs significantly. In addition, when the structure is subjected to seismic loads, the soil-structure interaction effects cannot be neglected. To manage these issues, this paper proposes an equivalent damping ratio for mixed structures by means of a semi-empirical error minimization method which considers soil-structure interaction. The results of numerical simulations indicate that the use of the equivalent damping ratios makes the results of dynamics analyses closer to the ones obtained by the actual damping ratios. Consequently, proposed method provides a much better approximation than the case in which the conservative overall ratio of 2% or 5% is used.

Local site conditions have a strong effect on ground response during earthquakes. Two important soil parameters that control the amplification effects of seismic motions by a soil column are the soil hysteretic damping ratio and shear wave velocity. This paper presents the results of in situ damping ratio measurements performed using continuous surface wave attenuation data at a site in Semnan University campus and analysis used to obtain the near surface soils damping ratio profile. Once the frequency dependent attenuation coefficients are determined, the shear damping ratio profile is calculated using an algorithm based on constrained inversion analysis. A computer code is developed to calculate the shear damping ratio in each soil layer. Comparisons of the in situ shear damping ratio profile determined from continuous surface wave with cross hole independent test measurements are also presented. Values of shear damping ratio, obtained using continuous surface wave measurements, were less than the measured using cross hole tests, possibly because of the higher frequencies used in cross hole tests.

Gravel-Clay mixtures are abundant materials in nature and are frequently used in certain civil engineering projects such as earth dams, levees and landfills. The advantage of using these soils lies in their low permeability owing to clay fraction along with the high shear strength due to the presence of the non-cohesive granular part. Karkheh dam is an example where these soils were used as the impervious core of the embankment. To date, little research has been carried out to investigate the performance of these soils, and therefore, their behavior under cyclic loading is still not well known. In order to investigate the cyclic behavior of gravel-clay mixtures, 51 cyclic and monotonic triaxial tests were performed on specimens with 11 different mixtures and under various confining pressures. Two different types of gravel, i.e. angular and round grains, were utilized to prepare specimens with the same gravel content in order to investigate the effect of the granule shape on the cyclic behavior of the mixtures. All the specimens were prepared with a constant compaction effort. Normalized shear modulus and damping ratio data showed differences in the behavior of mixtures with different kinds of gravel. Based on samples of macro structure performance under cyclic loading, two different mechanisms for the behavior of angular and round granules at contact level were hypothesized. The importance of the sampling method and specimen size for intermediate soils was also noticed.

1. Introduction: The dynamic response of liquid containers to the underground excitation has been studied intensively in recent years. In early investigations, the fluid response in rectangular liquid storage tanks was represented by impulsive and convective components [1]. The fluid was assumed to be incompressible and the container was assumed to have rigid walls. The Housner’s model [1] has been adopted in most of the current codes and standards for calculating the hydrodynamic pressures in concrete tanks. Very strong earthquakes in the United States and Japan caused heavy damage to many liquid storage tanks.

The use of dampers for retroftting and reducing seismic induced vibrations of structures is rising. Among all types of dampers, viscous and visco-elastic dampers are extensively used for buildings. Adding dampers increases equivalent damping ratio of structure which decreases displacement and member stresses. FEMA-356 has proposed an equation for calculating equivalent damping ratio of shear buildings with added dampers, based on the frst mode of vibration. In the present research, the goal was to study the accuracy of FEMA-356 formula for evaluating equivalent damping ratio with dampers as compared with the theoretical one. For the latter, the calculation is based on the hysteresis force-displacement response of the dampers. For obtaining hysteresis response, dynamic equation of motion of 2 to 12 stories 2D shear buildings equipped with viscous and visco-elastic dampers subjected to harmonic base excitation were solved. Both regular and mass distributed in height irregular structures with added dampers at all levels were considered. In addition to that, dampers were considered at random stories of the buildings and accuracy of equivalent damping ratios of FEMA-356 were evaluated. This study has shown that for viscous dampers, error of FEMA-356 formula in comparison with theoretical formula for viscous dampers would be in the range of 1 to 3 percent and for visco-elastic ones in which stiffness ratio of visco-elastic dampers to story shear stiffness is 10 percent, would be in the range of 1 to 17 percent. When the stiffness ratio is decreased to 5 percent, the error would decrease to 2, in the worst case. Also, it has been shown that mass irregularity in the height of the buildings increases the maximum error from 17% to 58% for viscoelastic dampers; no signifcant effect for viscous dampers. Moreover, addition of dampers in random stories of buildings up to six stories would increase error of FEMA-356 formula about 42 and 50 percent, respectively, for viscous and visco-elastic dampers.

The purpose of this paper is to evaluation the dynamic parameters of soil including damping ratio, shear modulus, elasticity modulus, and investigation of shear wave velocity in different sections, acquaintance with the methods of measuring each of these parameters and the effect of different conditions on these parameters. The research method is an overview of sources and references on soil dynamic parameters including damping ratio, shear modulus, modulus of elasticity and shear wave velocity. According to the results of this study, soil structure has a direct effect on soil dynamic properties and with increasing shear wave velocity the bed soil becomes harder and quality of soil will be better. Almost all construction projects are built on soil, so correct recognition of soil and identification dynamic parameters behavior of soil can be effective to providing a safe and economical design. Among the dynamic properties of soil, shear modulus, damping ratio and modulus of elasticity are more important and also there are various methods for measuring these parameters.

In this work effect of mass diffusion on the damping ratio in micro-beam resonators is investigated based on modified couple stress theory and the Euler-Bernoulli beam assumptions. The couple stress theory is a non-classical elasticity theory which is able to capture size effects in small-scale structures. The governing equation of a micro-beam deflection is obtained using Hamilton’s principle and also the governing equations of thermo-diffusive elastic damping are established using two dimensional non-Fourier heat conduction and non-Fickian mass diffusion models. Free vibration of the micro-beam resonators is analyzed using Galerkin reduced order model formulation for the first mode of vibration. A clamped-clamped micro-beam with isothermal boundary conditions at both ends is studied. The obtained results are compared with the results of a model in which the mass diffusion effect is ignored. Furthermore, the mass diffusion effects on the damping ratio are studied for the various micro-beam thicknesses, ambient temperature and length scales parameters. The results show that in the valid region, based on Euler-Bernoulli beam theory and before the critical thickness there is no difference between the results of mass diffusion and thermo-elastic damping and also the results indicate that by increasing the length scale parameter damping ratio decreases.

The damping ratio of chassis suspension is a key parameter for damping matching of in-wheel motor vehicles (IWMVs). Because the motor is attached to the driving wheel, the initial design method of the damping ratio for traditional cars is not entirely suitable for IWMVs. This paper proposes an innovative initial design method of the damping ratio for IWMVs. Firstly, a traveling vibration model of occupant-vehicle-road (OVR) for IWMVs is established. The model involves the occupant, cushion, suspension, in-wheel motor, road, and running speed. Secondly, on the basis of the model, using a special form of infinite integral, a mathematical expression of the occupant root-mean-square (RMS) acceleration is derived. Thirdly, based on the RMS optimization criterion for ride comfort, an 8 order polynomial equation about the suspension optimal damping ratio is deduced. Subsequently, through factors analysis, the change principles of the optimal damping ratio versus vehicle parameters are unveiled. Finally, the reliability of the optimal damping ratio is validated by test. The relative deviation of the calculated optimal damping ratio and the tested damping ratio is 5. 4%. The results show that the proposed optimal damping ratio can effectively guide the suspension damping matching for IWMVs.