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Current design codes generally use an equivalent linear approach for preliminary design of a seismic isolation system. The equivalent linear approach is based on effective parameters, rather than physical parameters of the system, and may not accurately account for the nonlinearity of the isolation system. The second chapter evaluates an alternative normalized strength characterization against the equivalent linear characterization. Following considerations for evaluation are included: (1) ability to effectively account for variations in ground motion intensity, (2) ability to effectively describe the energy dissipation capacity of the isolation system, and (3) conducive to developing design equations that can be implemented within a code framework. Although current code guidelines specify different seismic performance objectives for fixed-base and isolated buildings, the future of performance-based design will allow user-selected performance objectives, motivating the need for a consistent performance comparison of the two systems. Based on response history analysis to a suite of motions, constant ductility spectra are generated for fixed-base and isolated buildings in chapter three. Both superstructure force (base shear) and deformation demands in base-isolated buildings are lower than in fixed-base buildings responding with identical deformation ductility. To compare the relative performance of many systems or to predict the best system to achieve a given performance objective, a response index is developed and used for rapid prototyping of response as a function of system characteristics. When evaluated for a life safety performance objective, the superstructure design base shear of an isolated building is competitive with that of a fixed-base building with identical ductility, and the isolated building generally has improved response. Isolated buildings can meet a moderate ductility immediate-occupancy objective at low design strengths whereas comparable ductility fixed-base buildings fail to meet the objective. In chapter four and five, the life cycle performance of code-designed conventional and base-isolated steel frame buildings is evaluated using loss estimation methodologies. The results of hazard and structural response analysis for three-story moment resisting frame buildings are presented in this paper. Three-dimensional models for both buildings are created and seismic response is assessed for three scenario earthquakes. The response history analysis results indicate that the performance of the isolated building is superior to the conventional building in the design event. However, for the Maximum Considered Earthquake, the presence of outliers in the response data reduces confidence that the isolated building provides superior performance to its conventional counterpart. The outliers observed in the response of the isolated building are disconcerting and need careful evaluation in future studies.

La détermination des marges de sécurité des structures de Génie Civil potentiellement sujettes à un risque sismique important nécessite l'amélioration des capacités prédictives des codes de calcul actuellement utilisés. Les phénomènes d'amortissement restent à ce jour l'une des principales sources d'incertitudes, aussi bien au niveau de la structure que des matériaux constitutifs. Pourtant, la résistance de cette dernière à un séisme est fortement conditionnée par sa capacité à stocker et à dissiper l'énergie mécanique introduite par le mouvement du sol. De meilleures modélisations et estimations de ces effets sont donc indispensables à l’évaluation du risque sismique. Cette thèse s'inscrit dans le cadre du projet RSNR SINAPS@ dont l'objectif principal est le développement d'outils de modélisation permettant d'apprécier les effets des séismes, de la rupture de la faille jusqu'au comportement vibratoire des structures et équipements. / Assessment of safety margins related to a seismic risk in Civil Engineering requires the improvement of the predictive methods usually performed. The damping phenomena still remain a major source of uncertainty both at the structure and the constitutive material levels. However, the resistance of the said structure to an earthquake is strongly conditioned by its ability to store and to dissipate the energy introduced by the ground motion. Better modeling and evaluation of these effects are therefore essential for the seismic risk assessment. This thesis takes place in the framework of the RSNR SINAPS@ project whose main objective is the improvement of modeling tools allowing to appreciate the effects of an earthquake from the rupture of the fault to the vibratory behavior of the structures and amenities.

<p>The seismic risks to a structure or a set of structures in a region are usually determined by generating fragility curves that provide the probability of a building responding in a certain manner for a given level of ground motion intensity. Developing fragility curves, however, is challenging as it involves the computationally expensive task of obtaining the maximum response of the selected structures to a suite of ground motions representing the seismic hazard of the region selected. </p><p>This study presents a methodology to develop surrogate models for the prediction of the maximum responses of buildings to ground motion excitation. Data-driven surrogate models using simple machine learning techniques and physics-based surrogate models using the space mapping technique to map the low-fidelity responses obtained using a multi-degree of freedom shear building model to the high-fidelity values are developed for the prediction of the maximum roof drift ratio and the maximum story drift ratio of a chosen 15-story steel moment-resisting frame building with varying structural properties in California. The predictions of each of these surrogate models are analyzed to assess and compare the performance, capabilities, and limitations of these models. Best practices for developing surrogate models for the prediction of maximum responses of structures to ground motion are recommended.</p><p>The results from the development of data-driven surrogate models show that the spectral displacement is the best intensity measure to condition the maximum roof drift ratio, and the spectral velocity is the best intensity measure to condition the maximum story drift ratio. Fragility analysis of the structure is thus conducted using maximum story drift as the engineering demand parameter and spectral velocity as the intensity measure. Monte Carlo simulation is conducted using the physics-based surrogate model to estimate the maximum story drifts for ground motions that are incrementally scaled to different intensity levels. Maximum likelihood estimates are used to obtain the parameters for a lognormal distribution and the 95% confidence intervals are obtained using the Wald confidence interval to plot the fragility curves.</p><p>Fragility curves are plotted both with and without variations in the structural properties of the building, and it is found that the effects of variability in ground motions on the fragility are far higher than the effects of the randomness of structural properties. Finally, it is found that about 65 ground motion records are needed for convergence of the parameters of the lognormal distribution for plotting fragility curves by using Monte Carlo simulation.</p>

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Traditional seismic load resisting systems in buildings are designed to undergo inelastic deformations in order to dissipate energy, resulting in residual displacements. This work explores an approach to eliminate these residual displacements. The systems investigated have low initial stiffness which increases at a predefined displacement, and are therefore called stiffening elastic systems. This thesis begins with an examination of single-degree-of-freedom stiffening elastic systems. A case study is presented which suggests that the benefits from stiffening elastic behavior may be limited to systems which would have long periods if designed traditionally. A thorough parameter study is also presented which indicates the benefit of stiffening elastic behavior for SDOF systems with periods greater than four seconds. A final case study is presented that compares the response of a twelve-story stiffening elastic system to a ductile system and an elastic system. The stiffening elastic system was able to eliminate the residual displacements inherent in a ductile system while lowering the base shear experienced by the elastic system, but is not clearly better than the ductile system because the base shear force was much higher.

Assessment of post-liquefaction residual strength is needed for the development of empirically-based, predictive correlations for earthquake engineering design. Previous practice commonly assigned negligible strengths to liquefied materials for engineering analysis, producing overly-conservative designs. Increasingly available case history data, and improved analytical tools have allowed for more accurate and less overly-conservative estimation of soil residual strength, improving empirical predictive models. This study provides a new case history to the limited suite of (approximately 30) liquefaction failure case histories available for post-liquefaction in-situ strength predictive correlations. This case history documents the Las Palmas gold mine tailings dam failure, resulting from seismic-induced liquefaction during the moment magnitude 8.8 February 27, 2010 Maule, Chile earthquake; the sixth largest since 1900. Forensic analysis provides reasonably well-constrained values of 1) back-calculated representative post-liquefaction residual strength, 2) representative penetration resistance, and 3) representative vertical effective stress along the suspected liquefied failure surface. This study employs the incremental momentum method to incorporate momentum effects of a moving soil mass. The incremental momentum method requires a series of cross sections animating the geometry of failure progression from initiation to termination, converging on the observed final geometry. Using interpreted soil strength characteristics, an iterative procedure approximates the back-calculated value of post-liquefaction residual strength. Findings of this case history plot well with existing empirical deterministic regression charts and are in general agreement with previous, related efforts. Results yield representative, well-constrained values of: 1) post-liquefaction residual strength ≈ 173 psf, 2) penetration resistance of N1,60,CS ≈ 5 and N1,60 ≈ 2.5, and 3) vertical effective stress ≈ 4,300 lb/ft2, or ≈ 2.0 atm.

Rotating machines such as motors, generators, turbines, etc. are crucial mechanical components of modern industrial and power generation facilities. For proper functioning of these facilities during and after an earthquake, it is essential that the rotating machines in these facilities also function as desired. The dynamics of a rotating machine is quite complex. It is further complicated by the presence of earthquake induced base motions. The response spectrum methods, which are now commonly used for calculating seismic design response of civil structures, cannot be used as such for calculating the design response of rotating machines. In this thesis, a response spectrum method which can be applied to the rotating machines is developed. To develop the response spectrum approach, a generalized modal superposition method is utilized. The random vibration analysis is applied to incorporate the stochastic characteristics of the seismic inputs. The applicability of the proposed response spectrum approach is verified by a simulation study where fifty sets of acceleration time histories are used. The proposed method considers the fact that earthquake induced base motions have several components, including rotational inputs. To define the correlation between the rotational and translational input components of the excitation, the correlation matrix and a travelling seismic wave approaches are used. The numerical results are obtained to evaluate the effect of rotational input components on the response of a rotating machine. It is observed that the rotational components are important only when they are very strong. In actual practice, such strong rotational inputs are not expected to excite rotors which are either directly placed on ground or are placed in common buildings. In the proposed spectrum approach, nevertheless, the effect of rotational input components can be easily incorporated if the correlation between various excitation components is specified. / Master of Science

Soil liquefaction can cause devastating damage and loss and is a serious concern in civil engineering practice. One method for evaluating liquefaction triggering potential is a risk-targeted probabilistic approach that has been shown to provide more consistent and accurate estimates of liquefaction risk than traditional methods. This approach is a “performance-based” procedure which is based off of the performance-based earthquake engineering (PBEE) framework developed by the Pacific Earthquake Engineering Research (PEER) Center. Unfortunately, due to its complexity, performance-based liquefaction assessment is not often used in engineering practice. However, previous researchers have developed a simplified performance-based procedure which incorporates the accuracy and benefits of a full performance-based procedure while maintaining a more simplistic and user-friendly approach. Until now, these simplified performance-based procedures have only been available for the SPT (Standard Penetration Test). With the increasing popularity of the CPT (Cone Penetration Test), a simplified procedure is needed for CPT-based liquefaction assessment. This thesis presents the derivation of a simplified performance-based procedure for evaluating liquefaction triggering using the Ku et al. (2012) and Boulanger and Idriss (2014) models. The validation study compares the results of the simplified and full performance-based procedures. The comparison study compares the accuracy of the simplified performance-based and traditional pseudo-probabilistic procedures. These studies show that the simplified performance-based procedure provides a better and more consistent approximation of the full performance-based procedure than traditional methods. This thesis also details the development of the liquefaction loading maps which are an integral part of the simplified method.

Earthquake-induced liquefaction can cause severe damage to infrastructure is a serious concern in civil engineering practice. Post-liquefaction settlement is one of the common effects of liquefaction. The ability to predict and quantify post-liquefaction free-field settlement is a crucial part of seismic design. Many approaches have been developed during the past 50 years to perform liquefaction hazard analysis. The performance-based earthquake engineering (PBEE) framework developed by the Pacific Earthquake Engineering Research (PEER) center is a probabilistic framework that can provide a more accurate and complete seismic hazard analysis than other traditional methods. However, the PBEE framework is not widely used in routine projects due to its complexity.Previous researches have been performed to develop simplified performance-based procedures that can combine the simplicity of a traditional method and the accuracy of the full performance-based method. Unfortunately, these simplified performance-based procedures are only available for SPT. With the increase use of CPT, there is a need to develop simplified performance-based procedures for CPT. This study develops simplified performance-based procedures for the assessment of post-liquefaction free-field settlement for CPT, using the Boulanger and Idriss (2014) and the Ku et al. (2012) triggering models. The Juang et al. (2013) model, which is a probabilistic version of the Ishihara and Yoshimine (1992) model, is used in this study to performance free-field settlement calculations. The simplified procedure is based on the idea of liquefaction reference parameter maps. Reference values obtained from these parameter maps are then adjusted, using correction equations, to site-specific conditions. This study presents the deviations of the correction equations for the simplified performance-based procedure. The simplified procedure will then be validated in which 18 cities across the United States are analyzed using both the simplified procedure and the full performance-based procedure. The simplified performance-based procedure is shown to reasonably estimate the results of the full performance-based procedure. Finally, a study is performed to compare the accuracy and consistency of the simplified performance-based and the conventional pseudo-probabilistic procedures. The simplified performance-based procedure is found to provide better approximations of the full performance-based procedure with more consistency and precision.