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.

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.

Effects of SSI on EPR™ In-Structure Response for a Rock Site: Coherent and Incoherent High Frequency Ground Motion

2010 ◽  
Author(s):  
James J. Johnson ◽  
Oliver Schneider ◽  
Werner Schuetz ◽  
Philippe Monette ◽  
Alejandro P. Asfura
Keyword(s):  
Ground Motion ◽  
High Frequency ◽  
Ground Motions ◽  
Free Field ◽  
Response Spectra ◽  
Frequency Content ◽  
Structure Response ◽  
Standard Design ◽  
Rock Site ◽  
High Frequency Content

Recently, probabilistic seismic hazard assessments (PSHAs) performed for hard sites world-wide have yielded uniform hazard response spectra (UHRS) with significant high frequency content, i.e., frequency content greater than 10 Hz. This high frequency content is frequently due to near-field relatively low magnitude events. It is well known that these high frequency ground motions are not damaging to ductile structures, systems, and components (SSCs). One method of addressing the effect of these high frequency ground motions on structure response is to take into account the incoherency of ground motion. Over the past 25 years, free-field ground motion has been recorded providing an adequate basis for the development of ground motion coherency functions necessary to assess the effect of incoherence on nuclear power plant structures. The subject of this study was the AREVA NP EPR™ (European Power Reactor) nuclear island (NI) standard design. The effect of incoherency of ground motion on in-structure response spectra (ISRS) was assessed for the NI founded on a stiff rock site and subjected to high frequency enhanced input for hard rock sites. The ISRS at numerous locations and directions in the structures were calculated and compared. SSI is shown to be an important phenomenon for structures founded on stiff sites and subjected to high frequency ground motions.

Conditioned Simulation of Ground-Motion Time Series at Uninstrumented Sites Using Gaussian Process Regression

2021 ◽  
Author(s):  
Aidin Tamhidi ◽  
Nicolas Kuehn ◽  
S. Farid Ghahari ◽  
Arthur J. Rodgers ◽  
Monica D. Kohler ◽  
...  
Keyword(s):  
Time Series ◽  
Gaussian Process ◽  
Ground Motion ◽  
San Francisco ◽  
Earthquake Engineering ◽  
Seismic Analysis ◽  
Ground Motions ◽  
Free Field ◽  
Gaussian Process Regression ◽  
Motion Time

ABSTRACT Ground-motion time series are essential input data in seismic analysis and performance assessment of the built environment. Because instruments to record free-field ground motions are generally sparse, methods are needed to estimate motions at locations with no available ground-motion recording instrumentation. In this study, given a set of observed motions, ground-motion time series at target sites are constructed using a Gaussian process regression (GPR) approach, which treats the real and imaginary parts of the Fourier spectrum as random Gaussian variables. Model training, verification, and applicability studies are carried out using the physics-based simulated ground motions of the 1906 Mw 7.9 San Francisco earthquake and Mw 7.0 Hayward fault scenario earthquake in northern California. The method’s performance is further evaluated using the 2019 Mw 7.1 Ridgecrest earthquake ground motions recorded by the Community Seismic Network stations located in southern California. These evaluations indicate that the trained GPR model is able to adequately estimate the ground-motion time series for frequency ranges that are pertinent for most earthquake engineering applications. The trained GPR model exhibits proper performance in predicting the long-period content of the ground motions as well as directivity pulses.

Empirical Site Amplification Modelling for Horizontal and Vertical Ground Motions in Taiwan

2020 ◽  
Author(s):  
Chun-Hsiang Kuo ◽  
Shu-Hsien Chao ◽  
Che-Min Lin ◽  
Jyun-Yan Huang ◽  
Kuo-Liang Wen
Keyword(s):  
Ground Motion ◽  
Amplification Factor ◽  
Ground Motions ◽  
Free Field ◽  
Site Amplification ◽  
Amplification Factors ◽  
Taipei Basin ◽  
Vertical Ground Motions ◽  
Vertical Ground ◽  
Site Amplification Factor

<p>Site amplification behavior are important in ground motion prediction. Seismic waves were amplified and caused significant building damages in the Taipei Basin by the 1986 Hualien offshore (subduction interface) and the 1999 Chi-Chi earthquakes (crustal), for which both of the epicentral distances were nearly 100 km. To understand local site amplifications in Taiwan, empirical site amplification factors for both horizontal and vertical ground motions are studied using recently constructed strong motion and site databases for the free-field TSMIP stations. Records of large magnitude earthquakes of M<sub>W</sub> larger than 5.5 from 1991 to 2016 were selected for this study. Site amplification factors at site conditions with Vs30 between 120 m/s to 1600 m/s and bedrock accelerations up to 0.8 g were evaluated using ratios of spectral accelerations at different periods. The reference site condition, i.e. the engineering bedrock, is assumed as Vs30 of 760 m/s (B/C boundary) in this study. Our empirical site amplification form are borrowed from the site response function of ASK14 and CY14 ground motion models in NGA-West2 project with slight modification. Therefore our site amplification model includes a linear amplification term and a nonlinear deamplification term. The coefficients of the empirical models were obtained by a nonlinear regression analysis using the selected Taiwan data. Site amplification factor is a function of Vs30 and spectral intensity in the model. Similar linear site amplification factor to the NGA models is derived in our model; however, more significant soil nonlinearity behavior than the NGA models is likely captured from the empirical data. The amplification factor in vertical component is smaller than that in horizontal.</p>

scholarly journals Hazard-consistent seismic losses and collapse capacities for light-frame wood buildings in California and Cascadia

2021 ◽  
Author(s):  
Robert E. Chase ◽  
Abbie B. Liel ◽  
Nicolas Luco ◽  
Zach Bullock
Keyword(s):  
Seismic Hazard ◽  
Ground Motion ◽  
Seismic Risk ◽  
Ground Motions ◽  
Spectral Shape ◽  
Economic Losses ◽  
Frequency Content ◽  
Crustal Earthquakes ◽  
Design Values ◽  
American Society

AbstractWe evaluate the seismic performance of modern seismically designed wood light-frame (WLF) buildings, considering regional seismic hazard characteristics that influence ground motion duration and frequency content and, thus, seismic risk. Results show that WLF building response correlates strongly with ground motion spectral shape but weakly with duration. Due to the flatter spectral shape of ground motions from subduction events, WLF buildings at sites affected by these earthquakes may experience double the economic losses for a given intensity of shaking, and collapse capacities may be reduced by up to 50%, compared to those at sites affected by crustal earthquakes. These differences could motivate significant increases in design values at sites affected by subduction earthquakes to achieve the uniform risk targets of the American Society of Civil Engineers (ASCE) 7 standard.

Empirical Terrain-Based Topographic Modification Factors for Use in Ground Motion Prediction

2017 ◽  
Vol 33 (1) ◽  
pp. 157-177 ◽  
Author(s):  
Manisha Rai ◽  
Adrian Rodriguez-Marek ◽  
Brian S. Chiou
Keyword(s):  
Ground Motion ◽  
Ground Motions ◽  
Prediction Equation ◽  
Motion Prediction ◽  
Topographic Effects ◽  
Ground Motion Prediction ◽  
Modeling Error ◽  
Data Set ◽  
A Site ◽  
The Relationship

We develop a model to predict topographic effects on ground motions using the NGA-West2 data set. Topography at a site is quantified using three parameters: smoothed curvature, smoothed slope, and relative elevation. We examine the relationship between the site residuals, which represent the average modeling error of the reference ground motion prediction equation at a station, and the three topographic parameters. Our analysis shows that there are statistically significant trends in site residuals with respect to relative elevation and smoothed curvature. We propose modification factors to the Chiou and Youngs (2014) model that account for topographic effects on both the median and the standard deviation. These factors are period dependent and are a function of the relative elevation at the site. The factors result in amplification on median by a factor as high as 1.13 at T = 0.5 s for higher values of relative elevation, and deamplification as low as 0.75 between T = 2 s to 3 s for lower values of relative elevations.

Simplified R-Factor Relationships for Strong Ground Motions

2003 ◽  
Vol 19 (1) ◽  
pp. 25-45 ◽  
Author(s):  
Isabel Cuesta ◽  
Mark A. Aschheim ◽  
Peter Fajfar
Keyword(s):  
Ground Motion ◽  
Ground Motions ◽  
Structural Systems ◽  
Code Design ◽  
Frequency Content ◽  
Design Spectrum ◽  
Strong Ground Motions ◽  
R Factor ◽  
N2 Method ◽  
Strong Ground

Recent studies have demonstrated the need to consider the ground motion frequency content in the development and use of R−μ−T relationships. Results from two different approaches to determining these relationships are unified in the present paper. Two bilinear R−μ−T/Tg relationships are recommended for most strong ground motions and structural systems. One is more accurate, while the other, more conservative relationship is used in FEMA 273, ATC-32, and the simple version of the N2 method. Both relationships are indexed by the characteristic period of the ground motion, Tg. Simple methods to determine Tg from smoothed design spectra and recorded ground motions are provided. Neither recommended relationships are applicable to the nearly harmonic ground motions that may be generated at sites containing soft lakebed deposits. An example illustrates the application of these relationships to a code design spectrum in both the acceleration-displacement and yield point spectra formats.

Free-Field Particle Velocity Recordings of the January 31, 1986 Northeastern Ohio Earthquake

1987 ◽  
Vol 58 (4) ◽  
pp. 111-117
Author(s):  
R. Street ◽  
A. Zekulin ◽  
M. Mann
Keyword(s):  
Ground Motion ◽  
Particle Velocity ◽  
Ground Motions ◽  
Free Field ◽  
Motion Model ◽  
Ground Motion Model ◽  
Western Pennsylvania ◽  
Coal Fields

Abstract The January 31, 1986 earthquake in northeastern Ohio triggered eight biast monitors in the coal fields of southeastern Ohio and one in western Pennsylvania at epicentral distances of 128 to 297 kilometers from the earthquake. Recordings of the free-field ground motions exhibit predominant frequencies of 1 to 10 Hz, and are consistent with the ground motion model proposed by Nuttli and Herrmann (1984) for the propagation of Lg waves.

Empirical Relationships for Frequency Content Parameters of Earthquake Ground Motions

2004 ◽  
Vol 20 (1) ◽  
pp. 119-144 ◽  
Author(s):  
Ellen M. Rathje ◽  
Fadi Faraj ◽  
Stephanie Russell ◽  
Jonathan D. Bray
Keyword(s):  
Ground Motion ◽  
Ground Motions ◽  
Earthquake Ground Motion ◽  
Rupture Directivity ◽  
Frequency Content ◽  
Deep Soil ◽  
Empirical Relationships ◽  
Strong Ground Motions ◽  
Site Classes ◽  
Strong Ground

The frequency content of an earthquake ground motion is important because it affects the dynamic response of earth and structural systems. Four scalar parameters that characterize the frequency content of strong ground motions are (1) the mean period (Tm), (2) the average spectral period (Tavg), (3) the smoothed spectral predominant period (To), and (4) the predominant spectral period (Tp). Tm and Tavg distinguish the low frequency content of ground motions, while To is affected most by the high frequency content. Tp does not adequately describe the frequency content of a strong ground motion and is not recommended. Empirical relationships are developed that predict three parameters (Tm, Tavg, and To) as a function of earthquake magnitude, site-to-source distance, site conditions, and rupture directivity. The relationships are developed from a large strong-motion database that includes recorded motions from the recent earthquakes in Turkey and Taiwan. The new relationships update those previously developed by the authors and others. The results indicate that three site classes, which distinguish between rock, shallow soil, and deep soil, provide a better prediction of the frequency content parameters and smaller standard error terms than conventional “rock” and “soil” site classes. Forward directivity significantly increases the frequency content parameters, particularly Tm and To, at distances less than 20 km. Each of the frequency content parameters can be predicted with reasonable accuracy, but Tm is the preferred because it best distinguishes the frequency content of strong ground motions.

scholarly journals Empirical Spectral Amplification Function for a Reference Site Near Keddara Dam in Algeria using Strong Motion Data.

2021 ◽  
Author(s):  
Faouzi Gherboudj ◽  
Toufiq Ouzandja ◽  
Rabah Bensalem
Keyword(s):  
Ground Motion ◽  
Reference Site ◽  
Ground Motions ◽  
Free Field ◽  
Strong Motion ◽  
Ambient Vibration ◽  
Motion Prediction ◽  
Ground Motion Prediction ◽  
Strong Motion Data ◽  
Motion Data

Abstract This paper deals with empirical spectral amplification function for a reference site (STK) near Keddara dam in Algeria using local strong ground motion of earthquakes of magnitudes Mw 4.0-6.8. Amplification function is obtained as the 5% damped mean spectral ratio of surface observed and the rock predicted ground motions and it is compared to the ambient vibration HVSR which shows a good agreement in terms of fundamental frequency and curve tendency. In addition, recorded ground motions are compared to surface predicted motion with modified GMPE, the site term of the local ground motion prediction equation is adjusted based on the obtained amplification function of the free field STK site. Examples of the M 6.8, M5.4 and M4.7 earthquakes show clearly the advantage of using the adjusted Ground Motion Prediction Equations (GMPE) for predicting surface ground motion. Site effect characterization and the adjusted GMPE presented in this study provide the basis elements toward partially non ergodic site specific-Probabilistic seismic hazard assessment (PSHA) application based on local strong motion data in Algeria.

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