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 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 Multi-Scale Study of The Small-Strain Damping Ratio of Fiber-Sand Composites

Polymers ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2476
Author(s):  
Haiwen Li ◽  
Sathwik S. Kasyap ◽  
Kostas Senetakis
Keyword(s):  
Dynamic Properties ◽  
Wide Spectrum ◽  
Damping Ratio ◽  
Polypropylene Fiber ◽  
Small Strain ◽  
Treatment Method ◽  
Fiber Content ◽  
Polypropylene Fibers ◽  
Test Results ◽  
Fiber Reinforced

The use of polypropylene fibers as a geosynthetic in infrastructures is a promising ground treatment method with applications in the enhancement of the bearing capacity of foundations, slope rehabilitation, strengthening of backfills, as well as the improvement of the seismic behavior of geo-systems. Despite the large number of studies published in the literature investigating the properties of fiber-reinforced soils, less attention has been given in the evaluation of the dynamic properties of these composites, especially in examining damping characteristics and the influence of fiber inclusion and content. In the present study, the effect of polypropylene fiber inclusion on the small-strain damping ratio of sands with different gradations and various particle shapes was investigated through resonant column (macroscopic) experiments. The macroscopic test results suggested that the damping ratio of the mixtures tended to increase with increasing fiber content. Accordingly, a new expression was proposed which considers the influence of fiber content in the estimation of the small-strain damping of polypropylene fiber-sand mixtures and it can be complementary of damping modeling from small-to-medium strains based on previously developed expressions in the regime of medium strains. Additional insights were attempted to be obtained on the energy dissipation and contribution of fibers of these composite materials by performing grain-scale tests which further supported the macroscopic experimental test results. It was also attempted to interpret, based on the grain-scale tests results, the influence of fiber inclusion in a wide spectrum of properties for fiber-reinforced sands providing some general inferences on the contribution of polypropylene fibers on the constitutive behavior of granular materials.

scholarly journals INFLUENCE OF MATERIAL DAMPING ON THE RESPONSE OF UNDERGROUND STRUCTURES SUBJECTED TO EARTHQUAKE

2020 ◽  
Vol 26 ◽  
pp. 64-70
Author(s):  
Veronika Pavelcová ◽  
Tereza Poklopová ◽  
Michal Šejnoha ◽  
Tomáš Janda
Keyword(s):  
Damping Ratio ◽  
Underground Structure ◽  
Eurocode 8 ◽  
Viscous Damping ◽  
Material Damping ◽  
Underground Structures ◽  
Fixed Boundary ◽  
Design Spectrum ◽  
Rayleigh Damping ◽  
Element Simulation

The paper describes a finite element simulation of the response of a real underground structure subjected to earthquake using GEO5 FEM program. It concentrates on the influence of material damping with respect to a specific type of boundary condition prescribed at the bottom of the analyzed domain. It is seen that considering material damping is inevitable particularly in case of so called fixed boundary conditions to arrive at meaningful results. This is demonstrated on an artificial earthquake generated according to a design spectrum defined in Eurocode 8. A viscous damping ratio combined with the results of eigenvalue analysis is used to derive parameters of Rayleigh damping for three specific scenarios promoting the approach based on the lowest natural frequency as sufficiently accurate for the present task.

Measurement of small-strain shear modulus Gmax of dry and saturated sands by bender element, resonant column, and torsional shear tests

2008 ◽  
Vol 45 (10) ◽  
pp. 1426-1438 ◽  
Author(s):  
Jun-Ung Youn ◽  
Yun-Wook Choo ◽  
Dong-Soo Kim
Keyword(s):  
Shear Modulus ◽  
Shear Wave ◽  
Shear Wave Velocity ◽  
Small Strain ◽  
Resonant Column ◽  
Test Results ◽  
Bender Element ◽  
Small Strain Shear Modulus ◽  
Torsional Shear ◽  
Saturated Sands

The bender element method is an experimental technique used to determine the small-strain shear modulus (Gmax) of a soil by measuring the velocity of shear wave propagation through a sample. Bender elements have been applied as versatile transducers to measure the Gmax of wet and dry soils in various laboratory apparatuses. However, certain aspects of the bender element method have yet to be clearly specified because of uncertainties in determining travel time. In this paper, the bender element (BE), resonant column (RC), and torsional shear (TS) tests were performed on the same specimens using the modified Stokoe-type RC and TS testing equipment. Two clean sands, Toyoura and silica sands, were tested at various densities and mean effective stresses under dry and saturated conditions. Based on the test results, methods of determining travel time in BE tests were evaluated by comparing the results of RC, TS, and BE tests. Also, methods to evaluate Gmax of saturated sands from the shear-wave velocity (Vs) obtained by RC and BE tests were investigated by comparing the three sets of test results. Biot’s theory on frequency dependence of shear-wave velocity was adopted to consider dispersion of a shear wave in saturated conditions. The results of this study suggest that the total mass density, which is commonly used to convert Gmax from the measured Vs in saturated soils, should not be used to convert Vs to Gmax when the frequency of excitation is 10% greater than the characteristic frequency (fc) of the soil.

scholarly journals Effect of The Shape of Cyclic Loading on Damping Ratio at Small Strains

1998 ◽  
Vol 38 (1) ◽  
pp. 111-120 ◽  
Author(s):  
Mladen Vucetic ◽  
Giuseppe Lanzo ◽  
Macan Doroudian
Keyword(s):  
Cyclic Loading ◽  
Damping Ratio ◽  
Small Strains

Free Vibration Test for Damping Characteristics of Hybrid Polyester Matrix Composite with Carbon Particles

2016 ◽  
Vol 11 ◽  
pp. 1-6
Author(s):  
K. Karthik ◽  
R. Rohith Renish ◽  
I. Irfan Ahmed ◽  
T. Niruban Projoth
Keyword(s):  
Free Vibration ◽  
Hybrid Composites ◽  
Glass Fibers ◽  
Damping Ratio ◽  
Mode Shapes ◽  
Vibration Test ◽  
Engineering Structures ◽  
Carbon Filler ◽  
Damping Characteristics ◽  
Free Vibration Test

In this research aims to study the damping characteristics of hybrid polymer composite, which can be used in engineering structures and in many other applications. Hybrid composites are namely Glass fiber and carbon filler reinforced with polyester and epoxy matrix have been prepared by vacuum bag molding fabrication technique. Then the free vibration test were conducted using FFT analyzer with Lab VIEW software. The damping ratio and natural frequency were investigated for fabricated composites. Then through ANSYS, the mode shapes and natural frequencies were determined and the results were compared with experimental results. The damping ratio increases with increased volume fractions of E-glass fibers for both the types of polymer composites. Vibrations are concerned to large structures such as aircraft, as well as small structures such as electronic equipments.

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