Centrifuge Studies of Topographic Effects: Dynamic Response Mechanisms

2021 ◽  
Author(s):  
Jacob Dafni ◽  
Joseph Wartman
Keyword(s):  
Ground Motion ◽  
Free Field ◽  
Centrifuge Modeling ◽  
Earthquake Ground Motion ◽  
Topographic Effects ◽  
Time Frequency ◽  
Geotechnical Centrifuge ◽  
Frequency Domains ◽  
Frequency Components ◽  
Zone Of Influence

ABSTRACT This article presents analyses of select experiments from a comprehensive geotechnical centrifuge program to investigate topographic effects in single-sided slopes. A unique benefit of centrifuge modeling is that it provides high-resolution measurements of a thoroughly characterized “site” while fully preserving physical processes. The analyses were performed in the time and time–frequency domains to investigate mechanisms that produced the topographic effects. The results indicate that resonance at the slope’s topographic frequency is the principal driver of topographic effects. Site and topographic effects may combine at a slope crest to produce high levels of overall amplification. When topographic amplification occurs, the topographic zone of influence will vary depending on the ground-motion wavelength and the influence of phasing when multiple frequency components are present in the ground motion. Ground-motion complexities such as phase differences in response between a slope and the adjacent free field may serve to either amplify or de-amplify earthquake ground motion near a slope.

Centrifuge Studies of Topographic Effects: Parametric Investigation

2021 ◽  
Author(s):  
Jacob Dafni ◽  
Joseph Wartman
Keyword(s):  
Ground Motion ◽  
Ground Motions ◽  
Free Field ◽  
Experimental Program ◽  
Topographic Effects ◽  
Frequency Content ◽  
Geotechnical Centrifuge ◽  
Centrifuge Models ◽  
Zone Of Influence ◽  
Motion Amplitude

ABSTRACT This article presents the results of a comprehensive geotechnical centrifuge experimental program to investigate topographic effects across a series of single-sided slopes. The experimental campaign considered a range of governing factors, including slope inclination and ground-motion amplitude, frequency content, and duration. The testing program was nondestructive, allowing the centrifuge models to be subjected to over 140 different ground motions. Clear evidence of topographic effects, including amplification and deamplification of ground motion, were observed. Topography modified the frequency content and amplitude of the ground motion such that at the slope crest (1) peak ground accelerations ranged from 50% less than to 200% greater than the free-field, and (2) ground-motion mean square frequency shifted by as much as 55%. Higher topographic amplification levels lead to a larger topographic zone of influence, which, on average, spanned a distance equal to the slope height (H) behind and 2H in front of (toward slope) the slope crest. Physical modeling in the centrifuge proved to be a powerful experimental technique for generating empirical data to analyze topographic effects in a systematic and repeatable manner.

The effect of soil-structure interaction on seismometer readings

1978 ◽  
Vol 68 (3) ◽  
pp. 823-843
Author(s):  
G. N. Bycroft
Keyword(s):  
Ground Motion ◽  
Soil Structure ◽  
Free Field ◽  
Soil Structure Interaction ◽  
Rigid Sphere ◽  
Elastic Space ◽  
Structure Interaction ◽  
Frequency Components ◽  
Low Shear

abstract Rocking and vertical and horizontal translations of typical “free-field” seismometer installations lead to magnification of the ground motion record. This magnification can be significant for the higher frequency components if the terrain has a relatively low shear-wave velocity. Seismometers placed on foundations which cover a significant part of a wavelength of a horizontally incident wave, experience an attenuated ground motion. A method of correcting the seismograms for these effects is given. Compliance functions for a rigid sphere in a full elastic space are derived and are used to show that, in practical cases, down-hole seismometer installations are not significantly affected by interaction. These compliance functions should be useful in discussing the soil structure interaction of structures erected on bulbous piles. They may be also used as the basis of a method of determining elastic constants of ground at depth, in situ, and at different frequencies.

A Study of Elasto-Plastic Response of Single Degree of Freedom System Using Artificial Ground Motions With Given Time-Frequency Characteristics

2010 ◽  
Author(s):  
Ichiro Ichihashi ◽  
Akira Sone ◽  
Arata Masuda ◽  
Daisuke Iba
Keyword(s):  
Ground Motion ◽  
Response Spectrum ◽  
Ground Motions ◽  
Frequency Characteristics ◽  
Earthquake Ground Motion ◽  
Time Frequency ◽  
Displacement Response ◽  
Earthquake Ground Motions ◽  
Design Response Spectrum ◽  
The Given

In this paper, a number of artificial earthquake ground motions compatible with time-frequency characteristics of recorded actual earthquake ground motion as well as the given target response spectrum are generated using wavelet transform. The maximum non-dimensional displacement of elasto-plastic structures excited these artificial earthquake ground motions are calculated numerically. Displacement response, velocity response and cumulative input energy are shown in the case of the ground motion which cause larger displacement response. Under the given design response spectrum, a selection manner of generated artificial earthquake ground motion which causes lager maximum displacement response of elasto-plastic structure are suggested.

scholarly journals Application of wavelet for seismic wave analysis in Kathmandu Valley after the 2015 Gorkha earthquake, Nepal

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Binod Adhikari ◽  
Subodh Dahal ◽  
Monika Karki ◽  
Roshan Kumar Mishra ◽  
Ranjan Kumar Dahal ◽  
...  
Keyword(s):  
Wavelet Transform ◽  
Random Process ◽  
Ground Motion ◽  
Structural Damage ◽  
Ground Motions ◽  
Vertical Motion ◽  
Earthquake Ground Motion ◽  
Kathmandu Valley ◽  
Time Frequency ◽  
Long Period

AbstractIn this paper, we estimate the seismogenic energy during the Nepal Earthquake (25 April 2015) and studied the ground motion time-frequency characteristics in Kathmandu valley. The idea to analyze time-frequency characteristic of seismogenic energy signal is based on wavelet transform which we employed here. Wavelet transform has been used as a powerful signal analysis tools in various fields like compression, time-frequency analysis, earthquake parameter determination, climate studies, etc. This technique is particularly suitable for non-stationary signal. It is well recognized that the earthquake ground motion is a non-stationary random process. In order to characterize a non-stationary random process, it is required immeasurable samples in the mathematical sense. The wavelet transformation procedures that we follow here helps in random analyses of linear and non-linear structural systems, which are subjected to earthquake ground motion. The manners of seismic ground motion are characterized through wavelet coefficients associated to these signals. Both continuous wavelet transform (CWT) and discrete wavelet transform (DWT) techniques are applied to study ground motion in Kathmandu Valley in horizontal and vertical directions. These techniques help to point out the long-period ground motion with site response. We found that the long-period ground motions have enough power for structural damage. Comparing both the horizontal and the vertical motion, we observed that the most of the high amplitude signals are associated with the vertical motion: the high energy is released in that direction. It is found that the seismic energy is damped soon after the main event; however the period of damping is different. This can be seen on DWT curve where square wavelet coefficient is high at the time of aftershock and the value decrease with time. In other words, it is mostly associated with the arrival of Rayleigh waves. We concluded that long-period ground motions should be studied by earthquake engineers in order to avoid structural damage during the earthquake. Hence, by using wavelet technique we can specify the vulnerability of seismically active region and local topological features out there.

scholarly journals Time-Frequency Energy Distribution of Ground Motion and Its Effect on the Dynamic Response of Nonlinear Structures

2019 ◽  
Vol 11 (3) ◽  
pp. 702 ◽  
Author(s):  
Dongwang Tao ◽  
Jiali Lin ◽  
Zheng Lu
Keyword(s):  
Dynamic Response ◽  
Energy Distribution ◽  
Ground Motion ◽  
Peak Ground Acceleration ◽  
Structural Response ◽  
Ground Acceleration ◽  
Time Frequency ◽  
Plastic Structure ◽  
Perfectly Plastic ◽  
Frequency Components

The ground motion characteristics are essential for understanding the structural seismic response. In this paper, the time-frequency analytical method is used to analyze the time-frequency energy distribution of ground motion, and its effect on the dynamic response of nonlinear structure is studied and discussed. The time-frequency energy distribution of ground motion is obtained by the matching pursuit decomposition algorithm, which not only effectively reflects the energy distribution of different frequency components in time, but also reflects the main frequency components existing near the peak ground acceleration occurrence time. A series of artificial ground motions with the same peak ground acceleration, Fourier amplitude spectrum, and duration are generated and chosen as the earthquake input of the structural response. By analyzing the response of the elasto-perfectly-plastic structure excited by artificial seismic waves, it can be found that the time-frequency energy distribution has a great influence on the structural ductility. Especially if there are even multiple frequency components in the same ground motion phrase, the plastic deformation of the elasto-perfectly-plastic structure will continuously accumulate in a certain direction, resulting in a large nonlinear displacement. This paper reveals that the time-frequency energy distribution of a strong ground motion has a vital influence on the structural response.

WAVELET-BASED ESTIMATION OF MODAL PARAMETERS OF A VEHICLE INVOLVED IN A FULL-SCALE IMPACT

2012 ◽  
Vol 10 (06) ◽  
pp. 1250057
Author(s):  
WITOLD PAWLUS ◽  
HAMID REZA KARIMI ◽  
KJELL G. ROBBERSMYR
Keyword(s):  
Frequency Analysis ◽  
Mode Shape ◽  
Time Domain ◽  
Time Domain Analysis ◽  
Modal Parameters ◽  
Damping Factor ◽  
Time Frequency ◽  
Major Mode ◽  
Frequency Domains ◽  
Frequency Components

In this paper, a wavelet-based approach is presented for estimation of vehicle modal parameters. The acceleration of a colliding vehicle is measured in its center of gravity — this crash pulse contains detailed information about vehicle behavior throughout a collision. Three types of signal analysis are elaborated here: time domain analysis (i.e. description of kinematics of a vehicle in time domain), the frequency analysis (identification of the parameters of the crash pulse in frequency domain), and the time-frequency analysis, which comprises those techniques that study a signal in both the time and frequency domains simultaneously, using Morlet wavelet properties. The frequency components of the recorded crash pulse are identified by determining the ridge of the wavelet coefficients matrix. Having knowledge of the natural frequency of the signal, the damping factor for a given mode shape of the signal is estimated. In this work the major frequencies of the crash pulse are determined and the damping factor for the major mode shape is identified. The comparative analysis between the current method's outcome, the response of a model established previously by using different approach and the behavior of a real car is performed and reliability of the actual methods and tools is evaluated.

scholarly journals Experimental Wavelet Analysis of Rotor-Rub Vibration Signal

2019 ◽  
Vol 8 (12) ◽  
pp. 1756-1759
Keyword(s):  
Frequency Analysis ◽  
Mechanical Vibration ◽  
Vibration Signal ◽  
Time Frequency Analysis ◽  
Signature Extraction ◽  
Time Frequency ◽  
Vibration Data ◽  
Vibration Sensors ◽  
Frequency Domains ◽  
Frequency Components

A common defective phenomenon in rotating machinery is rotor-casing rub that generates impacts when the rotor rubs against the stator. Vibration sensors and data analysis techniques are commonly used for fault signature extraction and mechanical systems diagnosis. In this paper, an experimental characterization of rotor-rub is made by time-frequency analysis by means of the wavelet transform. A rotor kit, equipped with a variable speed DC motor, an accelerometer and a data acquisition system are used to acquire the mechanical vibration data. Vibration signal in frequency and time-frequency domains are shown for no-rubbing, light, and severe rubbing cases. Results show that FFT is unable to report where in time particular components of rubbing appear. However, the time-frequency analysis is able to give location information in time to differentiate light from severe rubbing, and extract the main spectral components showing a spectrum rich in high frequency components, characteristic of this phenomenon.

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