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A practical yet realistic three‐dimensional (3D) constitutive model is presented for modeling the cyclic degradation behavior of soil. Such response can be attributed to pore pressure build‐up and loss of cementation, among other stiffness and strength degradation mechanisms. Extending an existing multi‐yield surface (MYS) plasticity formulation, the cyclic degradation model (CDM) is developed by incorporating a novel degradation logic in terms of accumulated plastic strain or as prescribed by the user. Thereafter, the CDM is implemented into a computational framework (OpenSees), and Finite Element (FE) calibrations are undertaken to match the available experimental data at the element and system levels. A generally good agreement between the FE simulations and centrifuge test data demonstrates the CDM's capabilities to simulate the seismic response of sloping sites. Using the calibrated model properties, full 3D FE simulations of a large‐scale multi‐span bridge configuration, motivated by details of an actual bridge system in sloping ground, are conducted to highlight the underlying response mechanisms. In addition, computed results including and precluding the effects of cyclic degradation are directly compared and discussed. It is shown that loss of soil strength and stiffness play a noticeable role in the resulting ground and bridge response. Overall, the newly developed constitutive model and findings are of importance for a wide range of soil formations where cyclic degradation occurs under earthquake loading. [ABSTRACT FROM AUTHOR]

Traditional deterministic approaches for estimating liquefaction-induced settlement (LIS) do not account for uncertainties associated with earthquake loading and soil spatial variability. A numerical–probabilistic method for evaluating LIS that accounts for these uncertainties is developed. An advanced non-linear soil constitutive model is employed in numerical simulations and verified against VELACS experiment. Thereafter, CPT data from an alluvial plain in India together with scaled accelerograms are used to generate a big dataset. This dataset is implemented in regression machine learning algorithms for prediction of LIS. Of the adopted algorithms, it is observed that the XGBoost algorithm performs best with mean r2 of 0.980, mean MSE of 0.032, and mean EV of 0.980. The developed methodology is validated by comparing the predicted LIS with data from 21 case histories and the predicted magnitude are in reasonable agreement with reported values. A ready to use open-source program is developed that enables the practitioners to quantify the LIS. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of seismic loads on tunnels in an attempt to provide better protection from earthquake shaking. Dynamic analysis of angular offset tunnels was performed, and the tunnels' behavior under earthquake shaking and their response when using seismic isolation were analyzed in detail. The time history analysis was used to compute the stresses and deformation that develop in the tunnels during seismic events. Earthquake records with different frequency spectra were applied as seismic excitation to the twin tunnels. The excitation was applied normally to the tunnel axis, with peak ground accelerations of 0.10 g–0.30 g. The seismic event lasted 15 s, with a time step of 0.02 s utilized in the numerical analysis. Finite element modeling was employed to simulate the soil–tunnel interaction. Numerical models simulated twin tunnels passing through soft clay or stiff clay, with various earthquake records applied as seismic inputs. The effects of a silicon-based isolation material composed of silicon oil and fly-ash were compared with the use of traditional grout. The numerical model results show how seismic isolation affects the stresses and deformations that happen in tunnel bodies during earthquakes. [ABSTRACT FROM AUTHOR]

Site amplification studies and building code provisions recognize that soil liquefaction can alter the characteristics of ground shaking at a site. However, guidance as to how the amplitudes of spectral accelerations are modified is lacking. In this paper, available recorded ground motions from shallow crustal earthquakes at sites that exhibited evidence of liquefaction are investigated. Analysis of residuals computed relative to Next Generation Attenuation (NGA) estimates reveal positive bias at longer periods, slight negative bias at intermediate periods, and slight positive bias at short periods. Trends with V S 30, NGA-estimated peak ground acceleration (PGA), and moment magnitude are also observed. A model is developed that removes the initially observed residual bias and reduces uncertainty. The proposed model can be used to adjust NGA-estimated acceleration response spectra to account for the effects of liquefaction on ground shaking. [ABSTRACT FROM AUTHOR]

ABSTRACT Shake table tests were undertaken on an actual wind turbine (65 kW rated power, 22.6 m hub height and a 16 m rotor diameter) using the Network for Earthquake Engineering Simulation Large High Performance Outdoor Shake Table at the University of California, San Diego. Each base shaking event was imparted in two states, whereas the turbine rotor was still (parked), and while it was spinning (operational). Each state was tested in two orientations of shaking direction, one parallel (fore-aft) and another perpendicular (side-to-side) to the axis of rotation of the rotor. Structural response characteristics are presented for motions imparted in both configurations and both operational states. Modal parameters (natural frequencies, damping ratios and mode shapes) were estimated throughout the testing program. It is found that shaking imparted in the fore-aft direction while spinning is the only observed situation where operational effects appear significant, with reductions up to 33% in seismic bending moment demand near the tower base. Using modifications developed by the research team to the FAST code, experimental results are compared with corresponding simulations to show that dynamic characteristics, acceleration time histories and trends in tower bending seismic demand can be numerically approximated. This experimental evidence and associated numerical simulations suggest that modeling of combined wind and earthquake loading with existing turbine specific codes produce meaningful results. Discrepancies between experimental and numerical results support that further refinement of simulation codes can improve accuracy beyond the current state. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A full-scale shake table test is conducted to assess the seismic response characteristics of a 23 m high wind turbine. Details of the experimental setup and the recorded dynamic response are presented. Based on the test results, two calibrated beam-column finite element models are developed and their characteristics compared. The first model consists of a vertical column of elements with a lumped mass at the top that accounts for the nacelle and the rotor. Additional beam-column elements are included in the second model to explicitly represent the geometric configuration of the nacelle and the rotor. For the tested turbine, the experimental and numerical results show that the beam-column models provide useful insights. Using this approach, the effect of first-mode viscous damping on seismic response is studied, with observed experimental values in the range of 0.5-1.0% and widely varying literature counterparts of 0.5-5.0%. Depending on the employed base seismic excitation, damping may have a significant influence, reinforcing the importance of more accurate assessments of this parameter in future studies. The experimental and modeling results also support earlier observations related to the significance of higher modes, particularly for the current generation of taller turbines. Finally, based on the outcomes of this study, a number of additional experimental research directions are discussed. [ABSTRACT FROM AUTHOR]

Internet technologies are employed to allow real-time video monitoring, control, and execution of bench-top shake table experiments. Structural models of relevance to education in dynamics and earthquake engineering can be tested remotely over the Internet at any time. The underlying elements of experiment tele-observation and tele-operation/control are incorporated in a newly developed Web site. Tools for graphical display and analysis of recorded model response are included. Related education evaluation and assessment materials are prepared and made available on-line. The Web site currently provides an experimental component in courses such as earthquake engineering and structural dynamics. Based on a developed education assessment framework and the compiled student feedback, the Web site is found to be useful and effective. From this feedback, most students rated their experience as equivalent to the usual hands-on laboratory experiment. Similar applications in other areas of science and engineering will bring valuable experimentation content directly into the classroom, with efficient use of time and resources and the convenience of anywhere/anytime access. [ABSTRACT FROM AUTHOR]

A series of four dynamic centrifuge model tests was performed to investigate the effect of foundation densification on the seismic performance of a zoned earth dam with a saturated sand foundation. In these experiments, thickness of the densified foundation layer was systematically increased, resulting in a comprehensive set of dam-foundation response data. Herein, Class-A and Class-B numerical simulations of these experiments are conducted using a two-phase (solid and fluid) fully coupled finite element code. This code incorporates a plasticity-based soil stress–strain model with the modeling parameters partially calibrated based on earlier studies. The physical and numerical models both indicate reduced deformations and increased crest accelerations with the increase in densified layer thickness. Overall, the differences between the computed and recorded dam displacements are under 50%. At most locations, the computed excess pore pressure and acceleration match the recorded counterparts reasonably well. Based on this study, directions for further improvement of the numerical model are suggested. [ABSTRACT FROM AUTHOR]

Recent research clearly shows the importance of including the vertical component of earthquake ground motion in seismic analysis and design. In addition, pioneering studies [e.g., Elnashai and Papazoglou (1997)] have explored and documented the characteristics of available near-field vertical ground motion records. As a follow-up, this paper complements earlier studies, and investigates additional far-field records and available downhole array vertical motion records. A total of 111 free-field strong motion records (from California) and available downhole array records are employed. Compared to near-field records, far-field records generally contain more energy at longer periods. Based on the available data, response spectra are presented for near-field and far-field records respectively. The currently scarce downhole-array vertical motion records show that significant amplification may occur within the top 10–20 m soil layers. A simple one-dimensional (1D) vertical wave propagation model did not appear adequate for modelling the observed downhole array response. In using such a simplified model, very high viscous damping in the range of 15–25% was needed to match the recorded downhole vertical response, even for small tremors. Additional data and research are required [Beresnev et al., 2002] towards the development of a rational vertical motion site response analysis procedure. [ABSTRACT FROM AUTHOR]

Assessment of landfill seismic response necessitates the availability of reliable dynamic material properties. During the past decade, geophysical surveys and computational studies have been conducted to investigate the seismic response of the Operating Industries, Inc. (OII) landfill in Southern California. In this paper, a survey and summary of available research results is presented. In addition, a set of OII input-output seismic records during six earthquakes is thoroughly analysed. Spectral analyses are conducted to shed light on the landfill dynamic response characteristics. A simple shear beam model is found to be useful in modelling the landfill resonant behaviour. System identification techniques are employed to estimate the landfill stiffness and damping properties. These properties are defined by minimising the difference between computed and recorded acceleration response spectra at the landfill top. The identified stiffness properties are found to be near the lower bound of those documented through geophysical measurements. Identified damping of about 5% (at resonance) is within the range of earlier investigations. Comparisons of the computed and recorded accelerations show: (i) effectiveness of a linear viscous shear beam model in simulating the landfill dynamic behaviour, for the recorded small to moderate levels of dynamic excitation (up to 0.26 g peak lateral acceleration), and (ii) potential of the employed system identification procedure for analysis of input-output seismic motions. [ABSTRACT FROM AUTHOR]

Soil liquefaction and associated ground failures have been a major source of damage during the past earthquakes. The risk of liquefaction and associated ground deformation can be reduced by various ground-improvement methods including the stone column (gravel drain) technique. This paper presents the current state of the stone column technologies as a liquefaction countermeasure. A comprehensive review is provided aiming to: (a) identify key considerations for the general use of stone columns as a liquefaction countermeasure, (b) provide insights for design and construction, (c) compile the latest research developments, and (d) identify sources of useful information. Case histories of field applications and observed field performance are cited to portray different stone column applications and observed effectiveness. The paper identifies areas where more research is needed and includes recommendations for future research and development. [Copyright &y& Elsevier]

Widespread liquefaction occurred in Kobe, Japan, during the 1995 Hyogoken-Nanbu earthquake. At the reclaimed Port Island in Kobe, the observed large-scale liquefaction was documented by acceleration records from a downhole seismic array. Four accelerometers recorded the soil stratum response, from the ground surface down to a depth of 83 m. These recorded accelerations are used here to obtain direct estimates of the corresponding seismic shear stress and strain histories within the soil layers, which shed light on (1) the site seismic response during liquefaction and associated loss of soil stiffness at shallow depths near the ground surface; and (2) the virtually linear site response at deeper elevations. Response of the liquefied upper layer is characterized by cycles of large shear strain and very small shear stress. Conversely, the lower strata exhibited no sign of stiffness degradation throughout the earthquake. A computational simulation of this case history is performed in order to assess the mechanisms of site amplification and excess pore-pressure buildup. The results of this study demonstrate that acceleration histories recorded by downhole arrays represent a valuable direct source of information on site response during seismic excitation. [ABSTRACT FROM AUTHOR]

As exemplified in a state-of-the-art bridge-foundation-ground model simulation, a suite of new visualization techniques let scientists study seismic waves and interactively investigate and explore their data. In so doing, the techniques further scientific understanding and thus facilitate the development of new methods to protect real-world infrastructures against otherwise devastating earthquakes. [ABSTRACT FROM PUBLISHER]