When the excess pore water pressure generated during an earthquake dissipates in saturated loose sand, it causes post-liquefaction reconsolidation that can potentially yield substantial damage to the structure. To build resilient infrastructure, it is paramount to estimate these settlements as well as introduce soil reinforcement techniques to mitigate associated risks. Although there are abundant studies on liquefaction triggering assessment, the study of post-liquefaction settlement and the effects of stone columns as soil reinforcement is a relatively less established field. Generally, simplified empirical methods are employed for settlement evaluations. However, they possess several limitations such as the influence of non-liquefiable layers, soil fabric, permeability, and so on. Numerical models can be utilized to capture these effects with proper validation. This study evaluates the performance of stone columns in reducing seismically induced post-liquefaction settlement utilizing the Finite Element Method (FEM) and constitutive relationship, PM4Sand model, as it has been extended to account for reconsolidation settlement. The ability of the numerical framework to capture reconsolidation settlement is validated by replicating a shake table test performed on Ottawa F-55 sand. Results are compared with a previous numerical study inspired by the same experiment. After validation, a generic numerical model is proposed, and the performance of the natural ground and the reinforced ground is compared. A parametric analysis using 12 different ground motions is performed to assess the effect of varying ground motion intensity on the post-liquefaction settlement. The analysis is also performed with the conventional PM4Sand model (without the extension for reconsolidation). Finally, simulations are performed with a footing load above the soil model. The results demonstrate that (a) the presence of stone columns reduces post-liquefaction settlement, and (b) conventional constitutive models can highly underpredict post-liquefaction settlement. Further research is required to assess the effects of (a) 3D, (b) variations in permeability, (c) parametric analysis of stone columns, and (d) densification of stone columns. / Master of Science / When subjected to an earthquake, loose saturated sand may undergo liquefaction and exhibit a reduction in shear strength due to a rise in excess pore water pressure and the corresponding reduction in effective stress. This leads to failures associated with settlements resulting from the gradual dissipation of excess pore pressures. This mechanism results in post-liquefaction settlement. Several authors have investigated the mechanism of the post-liquefaction behavior of sand and proposed methodologies to assess the deformation caused by seismic loads. They mainly conclude that the reconsolidation mechanism is characterized by a decrease in the overall soil stiffness and an increase in permeability. Among different methodologies to quantify this settlement, finite element numerical modeling is the most widely used. The primary task in performing such numerical simulation is to select the best constitutive model (i.e., stress-strain relationships) that can accurately capture post-liquefaction behavior. In this study, the capabilities and limitations of the most common constitutive models are reviewed. Moreover, the efficacy of stone columns is also assessed to mitigate the risk posed by liquefaction. Firstly, the numerical framework is validated against data from a shake table test experiment. Then, a numerical model is proposed and subjected to different seismic motions. The settlement of the ground with and without stone columns is assessed and compared for all motions. In addition, the efficacy of stone columns is also analyzed by simulating the model with a footing load. Thus, this study provides insights into the effectiveness of stone columns under different seismic motions.

Seismic isolation systems are widely recognized as beneficial for protecting both acceleration- and displacement-sensitive nonstructural systems and components. Furthermore, adaptive isolation systems have been shown to enable engineers to achieve various performance goals under multiple hazard levels. These systems have been implemented for horizontal excitation, but there has been very limited research on isolation for vertical excitation. Thus, this paper seeks to evaluate the benefit of adaptive vertical isolation systems for component isolation, specifically for nuclear plants. To do this, three vertical isolation systems are designed to achieve multiple goals: a linear spring and a linear damper (LSLD), a linear spring and a nonlinear damper (LSND) and a nonlinear spring and a linear damper (NSLD). To investigate the effectiveness of the proposed systems, a stiff piece of equipment is considered at an elevated floor within a power plant. A set of 30 triaxial ground motions is used to investigate the seismic response of the equipment. The maximum isolation displacement and equipment acceleration are used to assess the effectiveness of the three isolation systems. While all systems significantly reduce the seismic accelerations on the equipment compared to the fixed-base case, a LSND system is shown to exhibit superior seismic performance across multiple hazard levels. / Thesis / Master of Applied Science (MASc)

Seismic isolation, in which a flexible layer is used to separate a structure from the ground below, is a proven method for reducing earthquake demands that has been recently introduced into the 2015 Canadian building code. Typical installations of seismic isolation use rigid diaphragms to bound the end plates of the isolators, which is easily implemented in new build scenarios but requires extensive excavation and foundation work in retrofit applications. An alternative form of isolation involves placing the isolation plane on top of first floor columns, potentially resulting in flexible boundary conditions. There have been very few experimental programs that mimic these flexible boundary conditions. To address conditions that may be found in column-top isolation design schemes, such as flexible framing and lightly axially loaded corner bearings, an experimental program on a quarter-scale column-top isolation system was conducted. The goals of the investigation were to investigate how rotations of both top and bottom bearing end plates impact key design assumptions such as horizontal stiffness, rotational stiffness, and stability, and how these effects change with axial load. Experimental findings showed that flexible boundary conditions reduce horizontal stiffness based on the sum of rotation at the ends, regardless of the rotation of one bearing end plate with respect to the other. This decrease is dependent on axial load, with more axial load leading to a higher decrease in horizontal stiffness. The rotational stiffness significantly decreases with bearing shear strain and models that use linear, elastic rotational springs underrepresent rotations at the boundaries. Lastly, traditionally used design limits for stability can be used for bearings of moderate shape factor (S1 = 19.6 used in testing) bounded by flexible framing, but these theoretical limits can overestimate the experimental determined limits by nearly double for bearings of low shape factors (S1 = 7.9 used in testing). / Thesis / Master of Applied Science (MASc) / Seismic isolation, in which a flexible layer is used to separate a structure from the ground below, is a proven method for reducing earthquake demands that has been recently introduced into Canadian building code. Typical installations of seismic isolation use rigid diaphragms to bound the end plates of the isolators, which is more easily implemented in new build scenarios but requires extensive excavation and foundation work in retrofit applications. An alternative form of isolation involves placing the isolation plane on top of first floor columns, potentially resulting in flexible boundary conditions. To address this, an experimental program on a quarter-scale column-top isolation system was conducted to investigate how rotations of both top and bottom bearing end plates impact key design assumptions such as horizontal stiffness, rotational stiffness, and stability. This research can help to expand the number and types of buildings isolation can be applied to, creating more resilient communities.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1981. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 91-93. / by Lucile Merrill Jones. / Ph.D.

We extend the application of the substructure synthesis method to more complex structures, and establish a design methodology for base isolation and active control in a distributed model of a building under seismic excitation. Our objective is to show that passive and active control complement each other in such an advantageous manner for the case at hand, that simple devices for both types of control are sufficient to achieve excellent response characteristics with very low control forces. The Rayleigh-Ritz based substructure synthesis method proved to be highly successful in analyzing a structure more complex than the ones previously analyzed with it. Comparing the responses of the hybridly controlled building and the conventional fixed building under El Centro excitation, we conclude that the stresses are reduced by 99.6 %, the base displacement is reduced by 91.7 % and the required control force to achieve this is 1.1 % of the building weight. / Ph. D.

New modal synthesis methods are developed for calculating the exact eigenproperties of structures divided into two substructures. Unlike the conventional mode synthesis techniques, here the synthesis of modes is carried out by solving a second eigenvalue problem by nontraditional means: the eigenvalues of the combined structure are obtained by solving simple characteristic equations which,in the proposed approach, can be defined in closed-form. These equations can be easily solved by a simple Newton-Raphson iterative scheme, especially when good initial estimates of the roots are available. Herein, explicit expressions are provided to calculate these initial values; these expressions are obtained via a second order matrix perturbation analysis of the algebraic eigenvalue problems. Once the eigenvalues are known, the eigenvectors can be calculated with closed-form expressions without solving any simultaneous equations. Several variants of the methods are developed to consider various damping cases which can be encountered in practice. Furthermore, for each damping case, two parallel approaches are developed that allow one to utilize two different types of modes - free and fixed attachment modes - of one of the substructures to be synthesized with the free attachment modes of the other structure. The eigenproperties of the combined system, once calculated, can be utilized in a mode superposition approach for the calculation of the system response for any forcing function . For seismic analysis of combined primary and secondary structures, such as a main structure supporting piping or other auxiliary system, the combined structure is divided into two substructures. The eigenproperties of these two substructures are then synthesized to obtain the eigenproperties of the combined system. To obtain response for seismic design motions defined in terms of ground response spectra, response spectrum approaches are presented which utilize the eigenproperties of the combined system. Closed-form formulas are presented to obtain any displacement-related response quantity of interest for the seismic input defined in terms of ground response spectra. The seismic response calculated by the proposed procedure accounts for the dynamic interaction effects between the primary and secondary structures and the nonclassically damped characteristics of the combined system in an analytically exact way. Numerical results showing the performance of the modal synthesis methods are presented. The applicability of the response spectrum approaches is verified by numerical simulation studies. The approach is applicable to light as well as heavy secondary structures equally effectively. It can also be used for seismic analysis of tertiary systems in industrial units. The potential application of the approach for efficient and accurate vibration analysis of aerospace and aircraft structures should also be of interest. / Ph. D.

Due to problems associated with welded moment connections uncovered after the Northridge earthquake, large bolted connections are becoming a much more attractive alternative for design in seismic regions. However, stringent design requirements established by the AISC Seismic Provisions for Structural Steel Buildings (1997) make current moment end-plate configurations and design procedures inadequate for multi-story buildings. This dissertation first examines and critiques current seismic design philosophies as applied to moment end-plate connections. Next, the finite element method is used to develop much-needed design procedures for large moment end-plate connections, and to improve the understanding of the role of geometric parameters (e.g., bolt pitch and stiffener locations) in the response of these connections. Finally, single-story and multi-story frames incorporating large moment end-plate connections with known moment-rotation characteristics are considered under seismic loading to determine the effectiveness of these systems in dissipating energy caused by the ground motion. / Ph. D.

A novel technique is investigated for utilizing the motion caused by environmental forces on a civil structure to generate electrical energy when the structure's response is within safety limits. When strong winds and earthquakes occur, the utility power source which supply energy to the actuator in an active control system is usually not reliable. With a regenerative electric actuator, recovered energy can be used to reduce the peak oscillations of the structure by applying forces (through actuators which use the recovered energy) counter to the environmental forces even if the utility power is not available. The use of a regenerative electric actuator allows a precise control of the amount of damping being provided by the actuator. Another advantage of using regenerative electric actuators is the reduction of the required energy capacity of the electrical source. This translates into lower energy ratings for the electrical source, and lower equipment and maintenance costs. This study is the first of its kind to propose and investigate active control of civil structures using regenerative electric actuators. This study is also the first of its kind to investigate the applicability of sliding mode control to civil structures using regenerative electric actuators. Sliding mode control provides a natural synthesis of the on-off nature of pulse width modulation control and control force saturation, and guarantees stability for the control law. It is also invariant to parameter changes and external disturbances. New direct-control schemes for neural network and adaptive fuzzy control of civil structures using regenerative electric actuators are proposed and investigated. These allow on-line control of the structure without the need for either an accurate model of the system or a specific learning stage. Since the error at the output of these controllers will be unknown in the direct-control scheme, the error at the system output is used to train or update the controller parameters. Simulations are conducted for wind and earthquake excitations using linear and nonlinear models. It is shown that the use of regenerative electric actuators is a viable and a reliable alternative for active control of civil structures. / Ph. D.

A new high-resolution 3-dimensional P-wave velocity model for Mt. Pinatubo volcano was developed by tomographic inversion of P-wave arrivals from 3,007 earthquakes recorded during a four month period from May to August, 1991. The arrivals were recorded by a network of seismic stations, consisting of seven pre-eruption stations and seven post-eruption stations. Two stations survived the June eruptions. First-arrival travel times were calculated using a finite-difference solution to the eikonal equation. An iterative, linearized approximation of the nonlinear tomography problem was used to solve separately for both velocity structure and hypocenter locations. Several inversions performed with different initial parameters and convergence schemes, and synthetic checkerboard reconstructions indicate a horizontal spatial resolution of velocity perturbations near 4 km. However, the network sparseness allows for a substantial trade-off between focal depth, origin time, and the vertical velocity profile. Many hypocenter clusters collapse from diffuse clouds into tighter features after 3-D relocation. These bands of earthquakes appear to represent fault-related structures. Three low-velocity (relative to the horizontal average) anomalies exist within the well-resolved portion of the velocity model. These anomalies are spatially associated with pre- and post-eruption earthquakes oriented along mapped surface fault zones. Similar anomalies observed at different volcanoes have been previously interpreted as magma related. The low-velocity anomalies at Pinatubo are interpreted as highly fractured, hot volumes of mostly competent rock, which may contain partial melt. / Master of Science

Remote sensing continues to be an invaluable tool in earthquake damage assessments and emergency response. This study evaluates the effectiveness of multilayer feedforward neural networks, radial basis neural networks, and Random Forests in detecting earthquake damage caused by the 2010 Port-au-Prince, Haiti 7.0 moment magnitude (Mw) event. Additionally, textural and structural features including entropy, dissimilarity, Laplacian of Gaussian, and rectangular fit are investigated as key variables for high spatial resolution imagery classification. Our findings show that each of the algorithms achieved nearly a 90% kernel density match using the United Nations Operational Satellite Applications Programme (UNITAR/UNOSAT) dataset as validation. The multilayer feedforward network was able to achieve an error rate below 40% in detecting damaged buildings. Spatial features of texture and structure were far more important in algorithmic classification than spectral information, highlighting the potential for future implementation of machine learning algorithms which use panchromatic or pansharpened imagery alone. / Master of Science