Temporal changes of seismic velocity and anisotropy in the shallow crust are quantified using local earthquakes recorded at a 200-m-deep borehole station CHY in Taiwan. This station is located directly above the hypocenter of the 10/22/1999, M6.4 Chia-Yi earthquake. Three-component seismograms recorded at this station show clear direct (up-going) and surface-reflected (down-going) P- and S-waves, and S-wave splitting signals. The two-way travel times in the top 200 m is obtained by measuring the time delays between the up-going and down-going waves in the auto-correlation function. The S-wave travel times measured in two horizontal components increase by ~1-2% at the time of Chia-Yi main shock, and followed by a logarithmic recovery, while the temporal changes of S-wave splitting and P-wave are less than 1% and are not statistically significant. We obtain similar results by grouping earthquakes into clusters according to their locations and waveform similarities. This suggests that the observed temporal changes are not very sensitive to the seismic ray path below CHY, but are mostly controlled by the variation of material property in the top 200 m of the crust. We propose that strong ground motions of the Chia-Yi main shock cause transient openings of fluid-filled microcracks and increases the porosity in the near-surface layers, followed by a relatively long healing process. Because we observe no clear changes in the shear wave anisotropy, we infer that the co-seismic damages do not have a preferred orientation. Our results also show a gradual increase of time delays for both the fast and slow S-waves in the previous 7 years before the Chia-Yi main shock. Such changes might be caused by variations of water table, sediment packing or other surficial processes.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23861号 / 工博第4948号 / 新制||工||1773(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 清野 純史, 教授 三村 衛, 准教授 古川 愛子 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

A comprehensive study of the soil shaking under the seismic wave-field ex- citation is presented. It includes theoretical, geological, geotechnical, data analysis and numerical simulations aspects. The aim is to quantify the main parameters allowing the estimate of the soil shaking in urban areas for better mitigating seismic risk due to future earthquakes. The city of Rome has been chosen as a case study because of its high density of popula- tion and large concentration of historical monuments with high earthquake vulnerability. This study improves significantly the knowledge concerning the detailed near-surface geology of the chosen study area of Rome, ful- fills the absence both of knowledge concerning its geotechnical properties and earthquake data recordings in the city. Among others, it allows for a better explanation of the spatial damage pattern observed in the city due to earthquakes in the past. The main innovations include the construction and long-term operation a seismic array in the city, analysis of the natural seismic noise, and instrumental recordings of the 2009 L'Aquila earthquake sequence. The 3D array (including a borehole sensor at 70-m depth) is the first one in Italy planned, realized and operated within an urban area, and the first one that recorded a significant earthquake in...

The objective of this study is to evaluate the regional differences between the worldwide based NGA-W1 ground motion models and available Turkish strong ground motion dataset and make the required adjustments in the NGA-W1 models. A strong motion dataset using parameters consistent with the NGA ground motion models is developed by including strong motion data from Turkey. Average horizontal component ground motion is computed for response spectral values at all available periods using the GMRotI50 definition consistent with the NGA-W1 models. A random-effects regression with a constant term only is used to evaluate the systematic differences in the average level of shaking. Plots of residuals are used to evaluate the differences in the magnitude, distance, and site amplification scaling between the Turkish dataset and the NGA-W1 models. Model residuals indicated that the ground motions are overestimated by all 5 NGA-W1 models significantly, especially for small-to-moderate magnitude earthquakes. Model residuals relative to distance measures plots suggest that NGA-W1 models slightly underestimates the ground motions for rupture distances within 100-200 km range. Models including the aftershocks over-predict the ground motions at stiff soil/engineering rock sites. The misfit between the actual data and model predictions are corrected with adjustments functions for each scaling term. Turkey-Adjusted NGA-W1 models proposed in this study are compatible with the Turkish strong ground motion characteristics and preserve the well-constrained features of the global models. Therefore these models are suitable candidates for ground motion characterization and PSHA studies conducted in Turkey.

The Central and Eastern United States (CEUS) is a region that is characterized by low frequency-high consequence seismic events such as the New Madrid sequence of 18111812. The infrequent nature of earthquakes in the region has led to a perception that the seismic risk in the area is low, and the current building stock reflects this perception. The majority of steel-framed buildings in the CEUS were designed without regard to seismic loads. Such frames possess limited seismic resistance, and may pose an unacceptable risk if a large earthquake were to occur in the region. A key ingredient of building performance and seismic risk assessment is the fragility, a term that describes the probability of failure to meet a performance objective as a function of demand on the system. The effects of uncertainties on building seismic performance can be displayed by a seismic fragility relationship. This fragility can be used in a conditional scenario-based seismic risk assessment or can be integrated with seismic hazard to obtain an estimate of annual or lifetime risk. The seismic fragility analyses in this study focus on steel frames that are typical of building construction in regions of infrequent seismicity; such frames have received little attention to date in building seismic risk assessment. Current steel building stock in Shelby Co., TN has been represented by five code-compliant model frames with different lateral force-resisting systems, i.e., braced-frames, partially-restrained moment frames and a rigid moment frame. The performance of model frames under certain hazard levels was assessed using fragility curves. Different rehabilitation methods were discussed and applied. Results indicate that PR frames behave better than expected and rehabilitated frames perform quite well even under severe earthquakes.

Maximum interstory drift and the distribution of this drift along the height of the structure are the main causes of structural and nonstructural damage in frame type buildings subjected to earthquake ground motions. Estimation of maximum interstory drift ratio is a good measure of the local response of buildings. Recent earthquakes have revealed the susceptibility of the existing building stock to near-fault ground motions characterized by a large, long-duration velocity pulse. In order to find rational solutions for the destructive effects of near fault ground motions, it is necessary to determine drift demands of buildings. Practical, applicable and accurate methods that define the system behavior by means of some key parameters are needed to assess the building performances quickly instead of detailed modeling and calculations. In this study, simple equations are proposed in order for the determination of the elastic interstory drift demand produced by near fault ground motions on regular and irregular steel frame structures. The proposed equations enable the prediction of maximum elastic ground story drift ratio of shear frames and the maximum elastic ground story drift ratio and maximum elastic interstory drift ratio of steel moment resisting frames. In addition, the effects of beam to column stiffness ratio, soft story factor, stiffness distribution coefficient, beam-to-column capacity ratio, seismic force reduction factor, ratio of pulse period to fundamental period, regular story height and number of stories on elastic and inelastic interstory drift demands are investigated in detail. An equation for the ratio of maximum inelastic interstory drift ratio to maximum elastic interstory drift ratio developed for a representative case is also presented.

Earthquake is undoubtedly one of the greatest natural disasters that can induce serious structural damage and huge losses of properties and lives. The resulting destructive consequences not only have made structural seismic analysis and design much more important but have impelled the necessity of more realistic representation of ground motions, such as inclusion of ground motion spatial variations in earthquake modelling and seismic analysis and design of structures. Recorded seismic ground motions exhibit spatial variations in their amplitudes and phases, and the spatial variabilities have an important effect on the responses of structures extended in space, such as long span bridges. Because of the multi-parametric nature and the complexity of the problems, the development of specific design provisions on spatial variabilities of ground motions in modern seismic codes has been impeded. Eurocode 8 is currently the only seismic standard worldwide that gives a set of detailed guidelines to explicitly tackle spatial variabilities of ground motions in bridge design, providing both a simplified design scheme and an analytical approach. However, there is gap between the code-specified provisions in Eurocode 8 and the realistic representation of spatially varying ground motions (SVGM) and the corresponding stochastic vibration analysis (SVA) approaches. This study is devoted to bridge this gap on modelling of SVGM and development of SVA approaches for structures extended in space under SVGM. A complete and realistic SVGM representation approach is developed by accounting for the incoherence effect, wave-passage effect, site-response effect, ground motion nonstationarity, tridirectionality, and spectra-compatibility. This effort brings together various aspects regarding rational seismic scenarios determination, comprehensive methods of accounting for varying site effects, conditional modelling of SVGM nonstationarity, and code-specified ground motion spectra-compatibility. A comprehensive, systematic, and efficient SVA methodology is derived for long span structures under tridirectional nonstationary SVGM. An absolute-response-oriented scheme of pseudo-excitation method and an improved high precision direct integration method are proposed to reduce the enormous computational effort of conventional nonstationary SVA. A scheme accounting for tridirectional varying site-response effect is incorporated in the nonstationary SVA scheme systematically. The proposed highly efficient and accurate SVA approach is implemented and verified in a general finite element analysis platform to make it readily applicable in SVA of complex structures. Based on the proposed SVA approach, parametric studies of two practical long span bridges under SVGM are conducted. To account for spatial randomness and variability of soil properties in soil-structure interaction analysis of structures under SVGM, a meshfree-Galerkin approach is proposed within the Karhunen-Loeve expansion scheme for representation of spatial soil properties modelled as a random field. The meshfree shape functions are proposed as a set of basis functions in the Galerkin scheme to solve integral equation of Karhunen-Loeve expansion, with a proposed optimization scheme in treating the compatibility between the target and analytical covariance models. The accuracy and validity of the meshfree-Galerkin scheme are assessed and demonstrated by representation of covariance models for various homogeneous and nonhomogeneous spatial fields. The developed modelling approaches of SVGM and the derived analytical SVA approaches can be applied to provide more refined solutions for quantitatively assessing code-specified design provisions and developing new design provisions. The proposed meshfree-Galerkin approach can be used to account for spatial randomness and variability of soil properties in soil-structure interaction analysis.

Une question fondamentale qui surgit dans le cadre de l’analyse probabiliste du risque sismique est le choix des indicateurs de nocivité des signaux sismiques. En plus de réduire la variabilité de la réponse structurelle (ou non structurelle),un indicateur amélioré (i.e. capable de mieux capturer les caractéristiques de nocivité des mouvements sismiques, aussi bien que l’alea sismique) fournit des critères moins stricts pour la sélection des signaux sismiques.Deux nouveaux indicateurs sont proposés dans cette étude: le premier, nommé ASAR (i.e. Relative Average Spectral Acceleration), est conçu pour la prévision de la demande structurelle, le second, nommé E-ASAR (i.e.Equipment Relative Average Spectral Acceleration), vise à prévoir la demande des composants non structuraux. Les performances des indicateurs proposés sont comparées avec celles des indicateurs de la littérature, sur la base de: a)milliers d’enregistrements sismiques ; b) analyses numériques conduites avec des modèles représentants différents types de bâtiments; et c) analyses statistiques rigoureuses des résultats. Selon l'étude comparative, les indicateurs développés s'avèrent être plus “efficaces” que les indicateurs couramment utilisés. D'ailleurs, l’ASAR et l’E-ASAR ont montré au propre la caractéristique de la “suffisance” en ce qui concerne la magnitude, la distance source-site, et le type de sol (VS30). De plus, les deux indicateurs originaux peuvent être calculés simplement avec la connaissance de la fréquence fondamentale du bâtiment. Cette caractéristique rend l’ASAR et l’E-ASAR facilement exploitables dans les études probabilistes d’alea sismique.Par conséquent, en raison de leur efficacité, suffisance, robustesse et formulation simple, l’ASAR et l’E-ASAR peuvent être considérés comme des candidats prometteurs pour la définition de l’alea sismique dans les cadres de l'analyse probabiliste et déterministe du risque sismique. / A fundamental issue that arises in the framework of Probabilistic Seismic Risk Analysis is the choice of groundmotion Intensity Measures (IMs). In addition to reducing record-to-record variability, an improved IM (i.e. one able tobetter capture the damaging features of a record, as well as the site hazard) provides criteria for selecting input groundmotions to loosen restrictions.Two new structure-specific IMs are proposed in this study: the first, namely ASAR (i.e. Relative Average SpectralAcceleration), is conceived for Structural demand prediction, the second namely, E-ASAR (i.e. Equipment-RelativeAverage Spectral Acceleration), aims to predict Non-Structural components acceleration demand. The performance ofthe proposed IMs are compared with the ones of current IMs, based on: a) a large dataset of thousands recordedearthquake ground motions; b) numerical analyses conducted with state-of-the-art FE models, representing actualload-bearing walls and frame structures, and validated against experimental tests; and c) systematic statistical analysesof the results. According to the comparative study, the introduced IMs prove to be considerably more “efficient” withrespect to the IMs currently used. Likewise, both ASAR and E-ASAR have shown to own the characteristic of“sufficiency” with respect to magnitude, source-to-site distance and soil-type (Vs30). Furthermore, both the introducedIMs possess the valuable characteristics to need (in order to be computed) merely the knowledge of the building’sfundamental frequency, exactly as it is for the wide-spread spectral acceleration Spa(f1). This key characteristic makesboth ASAR and E-ASAR easily exploitable in Probabilistic Seismic Hazard Analysis.Therefore, due to their proven efficiency, sufficiency, robustness and applicable formulation, both ASAR and EASARcan be considered as worthy candidates for defining seismic hazard within the frameworks of both Probabilisticand Deterministic Seismic Risk Analysis.

Le comportement nonlinéaire des sols observé lors des mouvements sismiques forts est maintenant bien admis et le déploiement des puits accélérométriques a permis des analyses détaillées de la propagation des ondes ainsi qu’une évaluation quantitative des paramètres physiques tels que la vitesse de cisaillement et de compression des ondes et les facteurs d’amortissements en fonction de la déformation. En dépit du nombre grandissant d’études sur ce phénomène, sa connaissance est encore récente et les recherches sur les données de puits accélérométriques restent une étape importante vers la compréhension du comportement complexe in-situ des sédiments soumis à des mouvements sismiques forts.L’objectif de ces travaux est triple. Premièrement, un code d’inversion par algorithme génétique est développé afin d’inverser des données de puits accélérométriques via la théorie des matrices de propagation de Thomson-Haskell. Cette technique nous permet dans un premier temps de valider la structure en une dimension (1D) (e.g., vitesse des ondes de cisaillement, facteurs d’ amortissements) d’un puits accélérométrique dans le domaine linéaire et dans un second temps de mettre en évidence de manière quantitative le comportement nonlinéaire des sédiments lors du séisme de Fukuoka, 2005, Japon. Deuxièmement, les résultats de l’inversion sont utilisés pour tester des lois de comportement simples et avancées en utilisant la Méthode des éléments Finis. Les résultats montrent clairement que l’hypothèse bi-linéaire de la loi de comportement simple produit des séries temporelles non réalistes en vitesse et en accélération. L’utilisation d’une loi de comportement avancée mène à de meilleurs résultats, cependant, le nombre de paramètres ajustables pour obtenir des résultats consistants avec l’observation est un obstable inévitable. Troisièmement, afin d’étendre l’étude des effets de site à des dimensions supérieures, des codes 2D et 3D de la Méthode en éléments Spectraux sont développés et validés en comparant leurs résultats dans le domaine linéaire avec ceux obtenus théoriquement ou via d’autres méthodes numériques. / Nonlinear behavior of soft soils observed during strong ground motions isnow well established and the deployment of vertical arrays (i.e., boreholestations) has contributed to detailed wave propagation analyses and the assessmentfor quantitative physical parameters such as shear-wave velocity,pressure-wave velocity and damping factors with respect to shear strain levels.Despite the growing number of studies on this phenomena, its knowledgeis still recent and research on borehole station data remains an importantstep toward the understanding of the complex in-situ behavior of soft sedimentssubjected to strong ground motions.The purpose of this work is threefold. First, an inversion code by geneticalgorithm is developed in order to inverse borehole stations data viathe Thomson-Haskell propagator matrix method. This technique allows usto validate the one-dimensional (1D) structure (e.g., shear-wave velocity,damping factors) of a borehole in the linear elastic domain and to showquantitative evidence of the nonlinear behavior of the soft sediments duringthe 2005 Fukuoka Prefecture western offshore earthquake, Japan. Second,the results of the inversion are used in order to test simple and advancedconstitutive laws using the Finite Elements Method. The results clearlyshow that the bi-linear assumption of the simple constitutive law producesunrealistic velocity and acceleration time histories. The use of the advancedconstitutive law leads to better results, however, the number of parametersto be tuned in order to obtain results consistent with the observation is anunavoidable obstacle. Third, in order to extend the study of site effects tohigher dimensions, 2D and 3D codes of the very efficient Spectral ElementsMethod are developed and validated by comparing their results in the lineardomain with those obtained theoretically or with other numerical methods.

<p> A method for tlie dynamic analysis· of planar coupled shear walls subjected to ground motions is developed herein. The method is capable of application to nonuniform coupled shear walls resting on flexible foundations. The possibility-of development of yield hinges at the ends of the connecting beams is included in the analysis . Also P-& Effect is incorporated in the stiffness of the structure. </p> <p> The method is based on the transfer matrix technique in combination with the continuum method. A step-by-step integration approach is used in solving the equation of motion. The response to a number of earthquake records are obtained. The effect of the rotational ductility factor of connecting beams is studied. </p> / Thesis / Master of Engineering (MEngr)