Book Section records
https://feeds.library.caltech.edu/people/Asimaki-D/book_section.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 28 Nov 2023 16:55:30 +0000Topography Effects Are Not Dominated by Ground Surface Geometry: A Site Effects Paradox
https://resolver.caltech.edu/CaltechAUTHORS:20170817-140923317
Authors: Mohammadi, K.; Asimaki, D.
Year: 2017
DOI: 10.1061/9780784480489.018
The material properties and the geometry of near surface soil layers, known as local site conditions, can significantly change the input seismic motion compared to the simple case of homogeneous linear elastic half-space. Our recent studies have shown that the effects of topography coupled to site response can lead to ground motion aggravation larger than the superposition of site and geometry amplification. These soil-topography coupling effects arise from seismic waves trapped in the near surface soil layers, are amplified or deamplified as a consequence of stiffness contrast, and are further modified due to scattering caused by irregular interface and ground surface. In this study, we investigate the coupling effects for 2D idealized convex features through a systematic analysis. The resulting trends, which are presented in the form of dimensionless amplification factors, clearly demonstrate the nonlinear nature of coupling effects, which cannot be predicted by modifying simulations of topography effects on rock by 1D site amplification factors, a posteriori. We then quantify these coupling effects through 3D site-specific analyses at selected strong ground motion stations in California, which yield more realistic amplification patterns (using 1 arc-second DEM extracted surface topographies and measured Vs profile). The results of coupling effects provide a basis as to how it can be incorporated in the proposed design motion of seismic code provisions.https://authors.library.caltech.edu/records/x64jj-6va61Parametric Estimation of Wave Dispersion for System Identification of Building Structures
https://resolver.caltech.edu/CaltechAUTHORS:20180521-143441555
Authors: Ebrahimian, Hamed; Kohler, Monica; Massari, Anthony; Asimaki, Domniki
Year: 2017
DOI: 10.1007/978-3-319-67443-8_70
The linear-elastic response of a building structure subjected to an earthquake base excitation can be approximated as the response of a continuous, spatially inhomogenous, dispersive, viscoelastic solid subjected to vertically incident plane shear waves. The frequency-dependent phase velocity and attenuation of seismic energy at different wavelengths, together with the inertial properties of the multilayer solid characterize the response of the building structure. The objective of this study is to identify the structural system by estimating the parameters that characterize the propagation of seismic waves in an equivalent multilayer viscoelastic solid. To pursue this objective, first, the measured dynamic responses of a building structure are used to derive the frequency response functions (FRFs) of the floor absolute acceleration with respect to the base excitation using a seismic interferometry approach. The FRFs obtained from the measured structural responses are then compared with the FRFs estimated using analytical models for one-dimensional shear wave propagation in a multilayer Kelvin-Voigt dispersive medium. Through a recursive Bayesian estimation approach, the parameters characterizing the phase velocity and damping ratio of the multilayer medium are estimated. This study provides a step forward in seismic interferometric identification of building structures by proposing a new method for parametric estimation of shear wave velocity and damping dispersion at the story level of a building structure. The estimated shear wave velocities before and after a damage-inducing event can be used to identify permanent loss of effective lateral stiffness of the building structure at the story level, thus can provide an alternative method for structural health monitoring and damage identification.https://authors.library.caltech.edu/records/2mnfg-fxr20On the Applicability of Shear Strain Index as a Proxy for Site Response Nonlinearity
https://resolver.caltech.edu/CaltechAUTHORS:20190522-152700336
Authors: Shi, Jian; Asimaki, Domniki
Year: 2018
DOI: 10.1061/9780784481462.053
Several recent studies have emphasized the advantages of conducting fully nonlinear site response analyses over the more conventional equivalent linear method, especially for strong ground motion and high frequency response predictions. Since the maximum soil shear strain (γ_(max)) reflects the degree of nonlinearity of the soil, recent studies have introduced the concept of a threshold γ_(max) to determine the conditions under which nonlinear analyses are necessary to provide credible site response predictions. However, as γ_(max) cannot be calculated a priori (i.e., before conducting any site response analysis), a proxy defined as the ratio of peak velocity of the input motion (PGV) to the time-averaged shear-wave velocity in the top 30 meters (V_(S30)), i.e., PGV/V_(S30), has been proposed instead. In this study, we quantify the appropriateness of PGV/V_(S30) (also referred to as shear strain index, Iγ) as a proxy for γ_(max), using a statistically significant number of ground motions and sites and using nonlinear site response simulations. We find that I_γ is a reliable proxy for γ_(max) only for sites with no sharp shear-wave velocity (V_S) impedance contrasts; otherwise it can underestimate γ_(max) by an order of magnitude or more. We lastly propose a correction factor called heterogeneity factor (HF), which is dependent on the velocity contrast of the V_S profile, and when applied upon I_γ, improves the mean and reduces the standard deviation of the I_γ – γ_(max) correlation.https://authors.library.caltech.edu/records/51j2y-0zg93Investigating the Applicability of Integrated Hydrological Modeling for Mapping Regional Liquefaction Hazard
https://resolver.caltech.edu/CaltechAUTHORS:20190522-145221319
Authors: Mital, Utkarsh; Rajasekaran, Eswar; Asimaki, Domniki; Das, Narendra N.
Year: 2018
DOI: 10.1061/9780784481462.066
Soil liquefaction and related phenomena, such as ground deformation and lateral spreading, pose significant risk to distributed and critical infrastructure systems. Although liquefaction vulnerability is controlled by geologic and groundwater conditions, its regional assessment is almost exclusively based on geologic material properties or proxies thereof. In this work, we are developing a multivariate methodology that incorporates groundwater conditions by introducing hydrological variables in regional assessment of liquefaction hazards. More specifically, we use remote sensing data and well-monitoring data to set up an integrated hydrological model that provides estimates of soil moisture and depth to water table. We demonstrate the methodology by presenting a case study from the 2010 El Mayor-Cucapah earthquake in Imperial County. We use reconnaissance data to train a logistic regression model, which yields probabilistic maps of liquefaction occurrence. Preliminary results indicate that the proposed approach may improve the modeling of regional liquefaction assessment at no additional site investigation cost. However, in order to draw quantitative conclusions on the accuracy improvements, more training data is necessary for which we are collaborating with the ARIA Center at JPL-Caltech.https://authors.library.caltech.edu/records/zvskz-qed59Bayesian Estimation of Nonlinear Soil Model Parameters Using Centrifuge Experimental Data
https://resolver.caltech.edu/CaltechAUTHORS:20190522-154056286
Authors: Seylabi, Elnaz Esmaeilzadeh; Ebrahimian, Hamed; Zhang, Wenyang; Asimaki, Domniki; Taciroglu, Ertugrul
Year: 2018
DOI: 10.1061/9780784481486.042
Calibration of nonlinear soil models from experimental data is an essential capability in research and engineering practice alike; however, this task is typically conducted by trial and error. In this study, we describe a Bayesian filtering technique, which is based on an unscented Kalman filter, to systematically assimilate data and estimate the parameters of a veritable soil plasticity model. We first verify the framework using a numerical example. Then, we use the technique to estimate the statistics of the parameters for a multiaxial plasticity model using data from a series of centrifuge tests and infer the maximum shear modulus G_(max), small strain damping, and shear modulus reduction curve G/G_(max). We show that the calibrated soil model, which has a vanished elastic range and a bounding surface, is successful in predicting the soil response for the range of input excitations used in the centrifuge tests. The technique is applicable to other soil models and can be implemented and utilized easily, provided that a standard interface to the soil material model is available.https://authors.library.caltech.edu/records/tvhd6-vzv65Basin Effects in Strong Ground Motion: A Case Study from the 2015 Gorkha, Nepal, Earthquake
https://resolver.caltech.edu/CaltechAUTHORS:20180629-082818097
Authors: Ayoubi, Peyman; Asimaki, Domniki; Mohammadi, Kami
Year: 2018
DOI: 10.1061/9780784481462.028
The term "basin effects" refers to entrapment and reverberation of earthquake waves in soft sedimentary deposits underlain by concave basement rock structures. Basin effects can significantly affect the amplitude, frequency, and duration of strong ground motion, while the cone-like geometry of the basin edges gives rise to large amplitude surface waves through seismic wave diffraction and energy focusing, a well-known characteristic of basin effects. In this research, we study the role of basin effects in the mainshock ground motion data recorded at the Kathmandu Basin, Nepal, during the 2015 M_w7.8 Gorkha earthquake sequence. We specifically try to understand the source of the unusual low frequency reverberating pulse that appeared systematically across the basin, and the unexpected depletion of the ground surface motions from high frequency components, especially away from the basin edges. In order to do that we study the response of a 2D cross section of Kathmandu Basin subjected to vertically propagating plane SV waves. Despite the scarcity of geotechnical information and of strong ground motion recordings, we show that an idealized plane-strain elastic model with a simplified layered velocity structure can capture surprisingly well the low frequency components of the basin ground response. We finally couple the 2D elastic simulation with a 1D nonlinear analysis of the shallow basin sediments. The 1D nonlinear approximation shows improved performance over a larger frequency range relative to the first order approximation of a 2D elastic layered basin response.https://authors.library.caltech.edu/records/97wkp-q1v14A Quasi-Static Displacement-Based Approximation of Seismic Earth Pressures on Rigid Walls
https://resolver.caltech.edu/CaltechAUTHORS:20190522-151131068
Authors: Garcia-Suarez, Joaquin; Asimaki, Domniki
Year: 2018
DOI: 10.1061/9780784481479.031
A number of linear-elastic solutions have been dedicated to resolve the problem of earth pressures on a rigid wall overlying rigid bedrock, among which, the classic solutions have been provided by Matsuo and Ohara (1960), Wood (1973), and Veletsos and Younan (1994). Wood's solution is mathematically involved (it requires evaluation of a double infinite sum) and the other two involve severe simplifying assumptions. An approximation procedure is presented to develop easy-to-evaluate estimates for the lateral earth thrust on rigid retaining walls under quasi-static loading. The procedure is based on the estimation of soil kinematic variables in the vicinity of the wall, from which strains, stresses, and total thrust are obtained. While the procedure is presented for quasi-static loading of a rigid wall overlaying rigid bedrock, this novel approach could be used to account for other complex effects that have been cumbersome to include in state-of-the art earth pressures procedures, such as dynamic loading, soil non-linear behavior, and wall compliance.https://authors.library.caltech.edu/records/9nsgy-x8g07A Nonlinear Model Inversion to Estimate Dynamic Soil Stiffness of Building Structures
https://resolver.caltech.edu/CaltechAUTHORS:20190522-151717317
Authors: Ebrahimian, Hamed; Ghahari, S. Farid; Asimaki, Domniki; Taciroglu, Ertugrul
Year: 2018
DOI: 10.1061/9780784481479.030
This study presents an output-only model inversion method to jointly estimate the model parameters and foundation input motions in structural models. The model inversion is based on Bayesian finite element model updating using the measured seismic response of the structure. The model parameters to be estimated consist of parameters characterizing the structural model, dynamic soil springs (to account for inertial soil structure interaction effects), and Rayleigh damping. We use the recorded response of the Millikan Library building to the 2002 Yorba Linda earthquake for validation study, in which the recorded structural responses are used to update the structural model resting on soil springs and dashpots. This study is a step forward towards developing model inversion methods that can be used with seismic response of real-world buildings to identify the Rayleigh damping and dynamic soil springs parameters.https://authors.library.caltech.edu/records/9r4py-f4b09A Modified Uniaxial Bouc-Wen Model for the Simulation of Transverse Lateral Pipe-Cohesionless Soil Interaction
https://resolver.caltech.edu/CaltechAUTHORS:20190522-150224679
Authors: Nguyen, Kien T.; Asimaki, Domniki
Year: 2018
DOI: 10.1061/9780784481479.003
This paper proposes a modified uniaxial Bouc-Wen model to evaluate reaction force-displacement backbone curve for transverse lateral pipe-cohesionless soil interaction. The model is capable of representing the nonlinearity and the smooth transition zone of the curve. Using unscented Kalman filter, the model parameter κ that controls the smoothness of transition zone is derived, on the basis of results from high-fidelity validated finite element analyses. κ is larger in loose sand compared to that in dense sand, implying a smoother transition zone of the curve for loose sand. There is a slight change of κ with pipe burial depth in case of dense sand, while the change is clearer and larger in loose sand. The variation of κ is related to the "passive-wedge" and "plow-through" failure mode of soil. The model is subsequently implemented in a series of soil-pipe interaction configurations, and the reaction force-deformation curves are found in good agreement with experimental data.https://authors.library.caltech.edu/records/7b8aq-7sh63On the complexity of seismic waves trapped in non-flat geologic features
https://resolver.caltech.edu/CaltechAUTHORS:20180814-143441650
Authors: Asimaki, Domniki; Mohammadi, Kami
Year: 2018
Most earthquake engineering and seismological models make the sweeping assumption that the world is flat. The
ground surface topography, however, has been repeatedly shown to strongly affect the amplitude, frequency, duration
and damage induced by earthquake shaking, effects mostly ignored in earthquake simulations and engineering design.
In this talk, I will show a collection of examples that highlight the effects of topography on seismic ground shaking, and I
will point out what these results suggest in the context of the current state-of-earthquake engineering practice. Examples
will range from semi-analytical solutions of wave propagation in infinite wedge to three-dimensional numerical
simulations of topography effects using digital elevation map-generated models and layered geologic features. I will
conclude by demonstrating that 'topography' effects vary strongly with the stratigraphy and inelastic behavior of the
underlying geologic materials, and thus cannot be accurately predicted by studying the effects of ground surface
geometry alone.https://authors.library.caltech.edu/records/bq5fa-jrb21Regional-Scale Geohazards Evaluation for Risk Assessment of Natural Gas Storage and Transmission Infrastructure
https://resolver.caltech.edu/CaltechAUTHORS:20220420-758142300
Authors: Zimmaro, Paolo; Wang, Pengfei; Asimaki, Domniki; Bullock, Zach; Rathje, Ellen M.; Ojomo, Olaide; Donahue, Jennifer L.; Bozorgnia, Yousef; Mosleh, Ali; Stewart, Jonathan P.
Year: 2021
DOI: 10.1061/9780784483688.008
Within the State of California, an extensive infrastructure of storage facilities and transmission pipelines provides natural gas to residential and commercial customers. A project funded by the California Energy Commission is developing a tool to evaluate the risk of this infrastructure system to earthquake hazards. This tool will have modules that characterize various hazards, infrastructure component fragilities, and system level risk.https://authors.library.caltech.edu/records/zp7aw-erw26