scholarly journals Material damping ratio from free-vibration method

2018 ◽  
Vol 50 (2) ◽  
pp. 83-97 ◽  
Author(s):  
Katarzyna Gabryś ◽  
Emil Soból ◽  
Wojciech Sas ◽  
Alojzy Szymański
Keyword(s):  
Free Vibration ◽  
Damping Ratio ◽  
Strain Range ◽  
Material Damping ◽  
Soil Behavior ◽  
Torsional Mode ◽  
Equivalent Viscous Damping ◽  
Number Of Cycles ◽  
Definition Of ◽  
Equivalent Viscous Damping Ratio

Abstract One important aspect of soil dynamics is attenuation or energy loses. This inherent dynamic property is essential in the analysis of soil behavior subjected to a dynamic load. Energy absorption in soils leads to the definition of an equivalent viscous damping ratio (D). In resonant column testing there are commonly two different approaches in measuring material damping: during a steady-state vibration (SSV), when the specimen is vibrated at its first mode; and during free-vibration decay (FVD). The study reports results associated with the small to medium strain range material damping from FVD method, i.e. there is a cut off the constant vibration of the specimen at resonance and the specimen is allowed to free-vibration mode while the decay strain amplitude during free-vibration is calculated. The experiments were conducted on cohesive soils (sasiCl, Cl, clSa) from various test sites located in Warsaw, Poland. All the specimens were subjected to torsional mode of vibration at their first natural frequency, at different mean effective stress. The authors paid particular attention to the number of successive cycles after the free-vibration of the material is initiated. They examined various propositions from the literature and compare the received damping values using different number of cycles of vibration. The results showed that the most stable values of material damping ratio can be obtained by selecting each time a line of best fit on the authors’ choice of number of free-vibration cycles. However, the number of these cycles should not exceed 10.

scholarly journals Energy-Based Design Criterion of Dissipative Bracing Systems for Seismic Retrofit of Frame Structures

2018 ◽  
Author(s):  
Gloria Terenzi
Keyword(s):  
Damping Ratio ◽  
Dissipative System ◽  
Design Criterion ◽  
Frame Structures ◽  
Element Analysis ◽  
Equivalent Viscous Damping ◽  
Linear Behaviour ◽  
Energy Based Design ◽  
Equivalent Viscous Damping Ratio ◽  
Reduction Factors

Direct sizing criteria represent useful tools in the design of dissipative bracing systems for the advanced seismic protection of existing frame structures, especially when incorporated dampers feature a markedly non-linear behaviour. An energy-based procedure is proposed herein to this aim, focusing attention on systems including fluid viscous devices. The procedure starts by assuming prefixed reduction factors of the most critical response parameters in current conditions, which are evaluated by means of a conventional elastic finite element analysis. Simple formulas relating the reduction factors to the equivalent viscous damping ratio of the dissipaters, ξeq, are proposed. These formulas allow calculating the ξeq values that guarantee the achievement of target factors. Finally, the energy dissipation capacity of the devices is deduced from ξeq, finalizing their sizing process. A detailed description of the procedure is presented in the article, by distinguishing the cases where the prevailing structural deficiencies are represented by poor strength of the constituting members, from the cases having excessive horizontal displacements. A demonstrative application to the retrofit design of a reinforced concrete gym building is then offered to explicate the steps of the sizing criterion in practice, as well as to evaluate the enhancement of seismic response capacities generated by the installation of the dissipative system.

scholarly journals Seismic Material Properties of Reinforced Concrete and Steel Casing Composite Concrete in Elevated Pile-Group Foundation

2015 ◽  
Vol 22 (s1) ◽  
pp. 141-148 ◽  
Author(s):  
Mi Zhou ◽  
Wancheng Yuan ◽  
Yue Zhang
Keyword(s):  
Reinforced Concrete ◽  
Seismic Performance ◽  
Damping Ratio ◽  
Pile Group ◽  
Ocean Engineering ◽  
Static Loads ◽  
Equivalent Viscous Damping ◽  
Static Tests ◽  
Equivalent Viscous Damping Ratio ◽  
Positive Effect

Abstract The paper focuses on the material mechanics properties of reinforced concrete and steel casing composite concrete under pseudo-static loads and their application in structure. Although elevated pile-group foundation is widely used in bridge, port and ocean engineering, the seismic performance of this type of foundation still need further study. Four scale-specimens of the elevated pile-group foundation were manufactured by these two kinds of concrete and seismic performance characteristic of each specimen were compared. Meanwhile, the special soil box was designed and built to consider soil-pile-superstructure interaction. According to the test result, the peak strength of strengthening specimens is about 1.77 times of the others and the ultimate displacement is 1.66 times of the RC specimens. Additionally, the dissipated hysteric energy capability of strengthening specimens is more than 2.15 times of the others as the equivalent viscous damping ratio is reduced by 50%. The pinching effect of first two specimens is more obvious than latter two specimens and the hysteretic loops of reinforced specimens are more plumpness. The pseudo-static tests also provided the data to quantitatively assessment the positive effect of steel casing composite concrete in aseismatic design of bridge.

Experimental Study on Seismic Responses of Piping Systems With Friction—Part 2: Simplified Analysis Method on the Effect of Friction

1995 ◽  
Vol 117 (3) ◽  
pp. 250-255
Author(s):  
H. Kobayashi ◽  
R. Yokoi ◽  
T. Chiba ◽  
K. Suzuki ◽  
N. Shimizu ◽  
...  
Keyword(s):  
Large Scale ◽  
Response Spectrum ◽  
Damping Ratio ◽  
Analysis Method ◽  
Equivalent Viscous Damping ◽  
Piping Systems ◽  
Simplified Analysis ◽  
Reduction Effect ◽  
Vibration Tests ◽  
Equivalent Viscous Damping Ratio

Friction between pipe and support structure is generally known to reduce seismic response of the piping systems. Vibration tests using large-scale piping model with friction support were carried out to evaluate the reduction effect. The piping response was mainly governed by the first modal deformation. The simplified analysis method based on linear response spectrum analysis was developed and confirmed to be applicable. In this method, the reduction effect by friction is treated as equivalent viscous damping ratio. This paper deals with the analysis method, and the comparison between the experimental results and analytical ones.

scholarly journals Novel Methods for the Computation of Small-Strain Damping Ratios of Soils from Cyclic Torsional Shear and Free-Vibration Decay Testing

Geotechnics ◽  
2021 ◽  
Vol 1 (2) ◽  
pp. 330-346
Author(s):  
Zhongze Xu ◽  
Yumeng Tao ◽  
Lizeth Hernandez
Keyword(s):  
Free Vibration ◽  
Ambient Noise ◽  
Damping Ratio ◽  
Small Strain ◽  
Material Damping ◽  
Viscous Material ◽  
Small Strains ◽  
Torsional Shear ◽  
Novel Methods ◽  
Decay Testing

This paper illustrates two novel methods for computing the small-strain hysteretic material damping ratio, λmin, of soils from the cyclic torsional shear (TS) and computing the small-strain viscous material damping ratio, Dmin, from the free-vibration decay (FVD) testing. Both λmin and Dmin are challenging to measure, due to the significant level of ambient noise at small strains (<10−4%). A two-step method is proposed combining the Fourier Transform and a phase-based data fitting method for torsional shear testing, and this method can effectively eliminate the ambient noise at small strains. A Hilbert Transform-based method is proposed for the free-vibration decay testing in order to achieve a more accurate measurement of the viscous material damping ratio, D, at different strain levels, especially at small strains. The improved λmin and Dmin at small strains are compared to data available in the literature. The two novel methods are shown to be accurate in computing the small-strain damping ratios.

scholarly journals Study on the Aging Time Variation Law of Mechanical Properties of the Laminated Rubber Bearing in Coastal Bridges considering Frictional Slip

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Yue Li ◽  
Chongming Gao ◽  
Chong Li ◽  
Qian Li
Keyword(s):  
Mechanical Properties ◽  
Aging Time ◽  
Damping Ratio ◽  
Viscous Damping ◽  
Equivalent Viscous Damping ◽  
Coastal Bridges ◽  
Shape Coefficient ◽  
Rubber Bearings ◽  
Frictional Slip ◽  
Equivalent Viscous Damping Ratio

As an important support member in the structural system of coastal bridges, the frictional slip and the rubber aging of laminated rubber bearings will affect the service safety of the overall structure in earthquakes. In order to investigate the mechanical properties aging law of the rubber bearings considering frictional slip in the coastal bridges, a frictional slip experiment was carried out on the laminated rubber bearings. Moreover, the influence of rubber aging on the mechanical properties of the bearings with various shape coefficients was analyzed by the finite element method during the 100 years of service life of bridges. The results indicate that (1) the horizontal and vertical stiffness of the bearing increase linearly with the aging time of the rubber. The amplification of the bearing stiffness also grows with the shape coefficient of the bearing. (2) The frictional slip initiation displacement of the bearing grows with the rubber aging time. Furthermore, the larger the shape coefficient of the bearing is, the more the frictional slip initiation displacement of the bearing increases. (3) With the increase of the aging time, the equivalent viscous damping ratio of the bearing continues to increase and more energy is consumed by frictional slip. For the bearing with the shape coefficient of 16.38, the equivalent viscous damping ratio at 100 years of rubber aging time is 1.17 times higher than that of the initial state of the bearing, and 33.21% more energy is consumed through frictional slip. Given that the marine environment accelerates rubber aging and changes the mechanical properties, the effects of the frictional slip and rubber aging properties of the laminated rubber bearings on the seismic dynamic response of bridges should be considered in the seismic design of coastal bridges.

Design and control performance of a frictional tuned mass damper with bearing–shaft assemblies

2019 ◽  
Vol 25 (12) ◽  
pp. 1812-1822 ◽  
Author(s):  
Jinwei Jiang ◽  
Siu Chun Michael Ho ◽  
Nathanael J Markle ◽  
Ning Wang ◽  
Gangbing Song
Keyword(s):  
Damping Ratio ◽  
Excitation Frequency ◽  
Structural Response ◽  
Tuned Mass Damper ◽  
Resonant Peak ◽  
Equivalent Viscous Damping ◽  
Optimal Damping ◽  
Mass Damper ◽  
And Control ◽  
Equivalent Viscous Damping Ratio

This paper explores the feasibility of leveraging the damping generated by the friction between movable flange-mounted ball bearings and a stationary shaft. This bearing–shaft assembly is integrated with a tuned mass damper to form a frictional tuned mass damper (FTMD). The friction coefficient and the equivalent viscous damping ratio of the proposed FTMD were experimentally obtained based on different cases of glass, steel, and aluminum slide shafts. The proposed FTMD was modeled and simulated numerically to study its ability to suppress vibrations on a single degree of freedom structure. Furthermore, a parallel experimental validation of the FTMD was also executed to verify simulation results. Results from both experiments and simulations demonstrated that the proposed FTMD device was able to significantly improve the damping ratio of the primary structure from 0.35% to 5.326% during free vibration, and also to suppress around 90% of uncontrolled structural response at a tuned frequency. In particular, the frequency responses, among the tested shaft materials, suggested that the selected steel slide shaft practically provided a near-optimal damping coefficient, thus the proposed FTMD was able to considerably reduce structural resonant peak amplitudes over the tested excitation frequency domain.

Predominant period and equivalent viscous damping ratio identification for a full-scale building shake table test

2017 ◽  
Vol 46 (14) ◽  
pp. 2459-2477 ◽  
Author(s):  
Michelle C. Chen ◽  
Rodrigo Astroza ◽  
José I. Restrepo ◽  
Joel P. Conte ◽  
Tara Hutchinson ◽  
...  
Keyword(s):  
Damping Ratio ◽  
Full Scale ◽  
Shake Table Test ◽  
Viscous Damping ◽  
Shake Table ◽  
Equivalent Viscous Damping ◽  
Predominant Period ◽  
Equivalent Viscous Damping Ratio

Viscoelastic Damping of Ortho-Planar Springs

2008 ◽  
Author(s):  
Sterling Anderson ◽  
Brian D. Jensen
Keyword(s):  
Damping Ratio ◽  
Spring Constant ◽  
Viscoelastic Damping ◽  
Viscous Damping ◽  
Constrained Layer Damping ◽  
Equivalent Viscous Damping ◽  
Background Theory ◽  
Modal Damping ◽  
Damping Treatments ◽  
Equivalent Viscous Damping Ratio

This paper presents the design of a damped ortho-planar spring that uses viscoelastic constrained-layer damping to reduce the free response oscillations of the spring and suppress modal resonances in that response. Background, theory, and applications surrounding fully-compliant ortho-planar springs and viscoelastic damping treatments are first discussed. Next, the effect of various constrained layer thickness on the spring constant, damping ratio, equivalent viscous damping ratio, modal frequencies, and modal damping ratios are compared, and trends discussed. The results show that the equivalent viscous damping co-efficient of the viscoelastically-damped spring can be increased to nearly 2.5 times that of the reference configuration without significantly changing the size of the constraining layer or the spring constant of the ortho-planar spring. Viscoelastically-damped ortho-planar springs are also shown to successfully remove mechanical noise from a contact resistance test stand.

Attenuation of Free Vibration Using Particle Impact Damper

2007 ◽  
Author(s):  
Hamid R. Hamidzadeh
Keyword(s):  
Free Vibration ◽  
Damping Ratio ◽  
Particle Impact ◽  
Constrained Layer Damping ◽  
Equivalent Viscous Damping ◽  
Impact Damper ◽  
Equivalent Damping ◽  
Vibrating System ◽  
Damping Characteristics ◽  
Moving Particle

The particle impact damper is an effective vibration damping treatment that can be used in the cases where visco-elastic constrained layer damping fails due to excessive surrounding temperature. In this type of passive damping, particles move in a container attached to the vibrating system resulting in plastic impact with the container. In the presented theoretical study, the damping characteristics of free oscillation for a vertical system with an initial displacement are considered and a governing equation for the system under free vibration with a particle damper is derived. To evaluate the damping characteristics for the free vibrating system, the equivalent damping ratio is determined by considering both kinematics and kinetics of the particle motion and its impacts with the container. The presented solution concludes that in general damping effectiveness can be enhanced by increasing the mass of the particle in comparison with total mass of the system. Mathematical optimum clearance for the moving particle and the equivalent viscous damping ratio are determined for the best performance of the particle impact damper.

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