Reliable earthquake ground-motion time histories are essential for seismic hazard analysis, structural design, and the risk assessment of distributed infrastructure systems. However, observed records of large earthquakes remain sparse, while physics-based simulations are computationally expensive and difficult to deploy at the scale required for uncertainty quantification. This thesis develops generative modeling frameworks for efficient, scenario-specific synthesis of earthquake ground motion, with an emphasis on neural operators, function-space learning, and scalable regional wavefield generation.
\r\n\r\nThe work begins with conditional generative adversarial neural operators for broadband three-component ground-motion synthesis at individual sites, conditioned on earthquake source, path, and site parameters. It then develops broader methodological foundations for functional generative modeling, including operator flow matching for stochastic-process learning and mesh-informed neural operators for domain- and discretization-agnostic generation on complex geometries. Building on these advances, the thesis introduces Ground-Motion Flow, a physics-inspired latent operator flow-matching framework for regional coherent ground-motion synthesis. By generating wavefields in a physics-aligned latent representation and reconstructing full spatiotemporal motions through neural operators, the framework produces spatially coherent earthquake wavefields conditioned on physical parameters with orders-of-magnitude acceleration relative to direct numerical simulation.
\r\n\r\nTogether, these studies establish a progression from single-site waveform synthesis to regional-scale, uncertainty-aware ground-motion wavefield generation. The results demonstrate the potential of functional generative models to complement physics-based simulation and empirical ground-motion modeling, opening a path toward fast, probabilistic, and scalable seismic hazard workflows for resilient infrastructure systems.
", "doi": "10.7907/3a27-v780", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:16838", "collection": "thesis", "collection_id": "16838", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11072024-033128289", "primary_object_url": { "basename": "Dassanayake_Sahangi_2025a.pdf", "content": "final", "filesize": 122088212, "license": "other", "mime_type": "application/pdf", "url": "/16838/27/Dassanayake_Sahangi_2025a.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Space Legos: A Concept for In-Space Assembly of Large Structures with a Stationary Robot", "author": [ { "family_name": "Dassanayake", "given_name": "D. M. Sahangi Pulsarani", "orcid": "0000-0002-1363-5764", "clpid": "Dassanayake-D-M-Sahangi-Pulsarani" } ], "thesis_advisor": [ { "family_name": "Pellegrino", "given_name": "Sergio", "orcid": "0000-0001-9373-3278", "clpid": "Pellegrino-S" } ], "thesis_committee": [ { "family_name": "Meiron", "given_name": "Daniel I.", "orcid": "0000-0003-0397-3775", "clpid": "Meiron-D-I" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Pellegrino", "given_name": "Sergio", "orcid": "0000-0001-9373-3278", "clpid": "Pellegrino-S" } ], "local_group": [ { "literal": "3MT Competition (Caltech)" }, { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "Human nature is inherently driven by the desire to build; advancing from primitive shelters to skyscrapers, and extending this relentless pursuit of progress to space through technological innovations. As space missions require larger and more complex structures, traditional deployable systems face challenges due to constraints on launch mass, volume, and complex deployment mechanisms. In-space assembly (ISA) offers a promising solution for constructing large structures, such as telescopes and satellites, directly in space.
\r\n\r\nThis thesis introduces a novel ISA concept with a centralized `truss builder' for autonomous assembly of polygonal-ring structures, using simple, repetitive operations and focusing on scalable mesh reflectors for communication and imaging. Utilizing the standard AstroMesh architecture, a rapid generalized design method is developed. Through the analysis of reflector geometry, optimized cable prestress, structural design, and a high-fidelity finite element model, analytical scaling laws are derived for mass, stowed envelope, and natural frequency based on aperture diameter. A semi-analytical homogenization model is introduced to efficiently predict fundamental natural frequencies. Stowed volume is a key limitation for large deployable reflectors, approaching current and future launch capacity limits, while the proposed ISA reflectors face no such constraints for apertures up to 200 meters.
\r\n\r\nA two-dimensional finite element model simulates the assembly kinematics of large ring-like structures with the proposed ISA concept, enhancing understanding of the process and evaluating key design aspects of a stationary robot assembling scalable ring-like trusses. The model provides insights for optimizing autonomous assembly systems and underscores the need for advanced numerical simulations to ensure smooth assembly and stability during ISA, especially as structures scale.
\r\n\r\nLab-scale prototype testing validates the ISA concept, with results aligning qualitatively with simulations. Both experiments and simulations reveal a range of viable solutions, demonstrating flexibility for future mission designs. This research offers crucial insights into the design and scaling of mesh reflectors, setting the stage for comparing ISA with traditional deployable systems. The proposed ISA concept presents a practical solution for building high-precision, large-scale structures in space, advancing the field of space construction and supporting future extended space missions.
", "doi": "10.7907/0pn5-3w42", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16133", "collection": "thesis", "collection_id": "16133", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07032023-235459528", "primary_object_url": { "basename": "Moncada_Rigoberto_2024_revised.pdf", "content": "final", "filesize": 62933757, "license": "other", "mime_type": "application/pdf", "url": "/16133/1/Moncada_Rigoberto_2024_revised.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Sea Ice Discrete Element Modeling: Melt and Fracture of Floes and Sheets", "author": [ { "family_name": "Moncada Lopez", "given_name": "Rigoberto", "orcid": "0000-0001-7655-5406", "clpid": "Moncada Lopez-Rigoberto" } ], "thesis_advisor": [ { "family_name": "Andrade", "given_name": "Jose E.", "orcid": "0000-0003-3741-0364", "clpid": "Andrade-J-E" } ], "thesis_committee": [ { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Thompson", "given_name": "Andrew F.", "orcid": "0000-0003-0322-4811", "clpid": "Thompson-A-F" }, { "family_name": "Andrade", "given_name": "Jose E.", "orcid": "0000-0003-3741-0364", "clpid": "Andrade-J-E" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Over the last 40 years, the Arctic Ocean has experienced a significant reduction in surface area and thickness of sea ice for its minimum summer and year-round values. Sea ice, existing both as continuous ice sheets and distinct broken floes or blocks, is disappearing earlier and faster over time. These changes are largely occurring within marginal ice zones, where ice is most vulnerable to thermal forcings from the sun, oceans, and atmosphere and wind and ocean currents. Given that sea ice plays a vital role in regulating climate by delaying global energy exchanges, its loss is a vital factor in increasing global temperatures and the frequency of extreme weather events. Understanding and projecting seasonal variations in sea ice is imperative to improve climate predictions. However, many of the processes in sea ice are not fully described by most existing models, due to the limitations of continuum sea ice approaches. As a result the use of discontinuum techniques on sea ice is a very active field. In this work, we combine discrete element methods with satellite image analysis to study changes in sea ice concentration and floe size distribution during the summer melt transition for ensembles of distinct floes decaying into open waters and continuous fast sea ice sheets breaking into multiple floes. For the pure floe-like behavior, we use the `Level Set Discrete Element Method for Sea Ice' or LS-ICE method. This model can resolve individual sea ice floes with realistic shapes, and represent their physical interactions by leveraging level-set functions to detect contacts. LS-ICE can also be coupled to atmospheric and oceanic heat and momentum forcings and simulate associated melt and breakage processes. With it, we are able to reproduce sea ice concentration decline for the summers of 2018 and 2020 at Baffin Bay. Using LS-ICE we also unveil the sensitivity of sea ice loss and floe size distribution to different intensities of fracturing and ocean/solar melt and how sea ice floe size determines which is more dominant. For monolithic landfast sea ice sheets, we use a bonded particle method within the level set discrete element model called LS-DEM-BPM. We explore the relationship between landfast sea ice breakage and area decline, ocean currents and floe size distribution for a region in Fram Strait in 2023. We also replicate its fracture characteristics, using idealized pulses and arbitrary eddying ocean currents, and unveil particular combinations of wavelengths and wave speeds that facilitate breakage. Our results give new insight on sea ice melt and breakage interactions and provide a numerical framework for simulating the complete transition of sea ice from intact sheets to open oceans.", "doi": "10.7907/erqr-cr51", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16265", "collection": "thesis", "collection_id": "16265", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12132023-225911259", "type": "thesis", "title": "Vibration Damping of Coiled Structures Through Frictional Slip", "author": [ { "family_name": "Wen", "given_name": "Alexander Huai-Cheng", "orcid": "0009-0008-9038-3039", "clpid": "Wen-Alexander-Huai-Cheng" } ], "thesis_advisor": [ { "family_name": "Pellegrino", "given_name": "Sergio", "orcid": "0000-0001-9373-3278", "clpid": "Pellegrino-S" } ], "thesis_committee": [ { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Pellegrino", "given_name": "Sergio", "orcid": "0000-0001-9373-3278", "clpid": "Pellegrino-S" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Watkins", "given_name": "Michael M.", "clpid": "Watkins-M-M" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "Vibration management is important for the survivability of structures. The response of a structure under vibration is dependent upon interaction between the excitation environment and the properties of the structure. If the input excitation cannot be adjusted, then the structure must be engineered to survive. One approach to engineering structures to reduce vibration response is through damping, which is achieved by adding damping devices or materials to covert kinetic energy into heat, where removing energy from the system reduces the amplitude of response. There are a variety of existing vibration damping concepts and techniques, however, conventional methods of these approaches are subject to limitations such as compromising stiffness for increased damping and performance that is excitation profile dependent.
\r\n\r\nThis research proposes a novel, passive vibration damping concept which is motivated by recent deployable structures for space that use coiling as a packaging architecture. The proposed concept, referred to as \"wound roll damping\", is a friction-based damping scheme for coiled structures, where the structure is wound around a mandrel with tension that allows interlayer slip during vibration. The friction between slipping layers provides an energy dissipation mechanism, which reduces the overall level of response. The concept was developed with the challenges of mitigating spacecraft launch vibration and the limitations of conventional damping techniques in mind.
\r\n\r\nUnderstanding of the working principle and performance of this damping concept is achieved using a combination of experiments, analysis, and FEA. A method for determining the locations of slip within a wound roll under vibration is presented. This consists of modeling the interlayer friction forces, using analytical expressions for the stress fields that arise during tension winding of wound rolls, and comparing these values against loading estimates obtained from analysis and FEA. The locations of slip for wound rolls supported by a cantilevered mandrel with bending vibration modes are towards the root of the wound roll structure, near the inner layers.
\r\n\r\nExperimental studies that demonstrate the performance and properties of this damping concept are presented in this work. A wound roll test sample is subjected to a range of excitation profiles including: sine sweep, sine dwell, random, and shock with varying levels of sample winding tension and excitation amplitude. Using these experiments, this concept is demonstrated to not be subject to the limitations of conventional damping schemes. This scheme is observed to be capable of significantly increasing the overall stiffness while providing elevated damping levels, with a performance that is tunable with winding tension, independent of excitation profile, and scales with excitation amplitude. The locations of slip are observed to be consistent with predictions from FEA and analysis.
\r\n\r\nTwo approaches to simulate and model the wound roll damper are developed to both better understand the physical mechanism of this concept and provide analysis tools. The first method is an FEA model, consisting of the base vibration of concentric shells and solids that have frictional contact interactions. The second method is a 2-DoF reduced order model that simulates the frictional contact between two mass-spring-damper systems. Both methods are demonstrated to have good correlation with experimental measurements.\r\n
\r\n\r\nA majority of this work demonstrates the performance of this concept, using both experiments and simulation at lab scales. This work also presents simulation studies that demonstrate the viability of this concept at realistic scales. Using simulations scaled to recent coilable space structures, both implemented and proposed, the wound roll damping concept is demonstrated to provide significant stiffness and damping.
", "doi": "10.7907/gvps-8x65", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16495", "collection": "thesis", "collection_id": "16495", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06042024-004152477", "primary_object_url": { "basename": "Ogren_Alex_2024.pdf", "content": "final", "filesize": 98164399, "license": "other", "mime_type": "application/pdf", "url": "/16495/4/Ogren_Alex_2024.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Machine Learning and Inference Methods for Surrogate Modeling and Inexpensive Characterization of Elastodynamic Systems", "author": [ { "family_name": "Ogren", "given_name": "Alexander Charles", "orcid": "0000-0002-7277-0069", "clpid": "Ogren-Alexander-Charles" } ], "thesis_advisor": [ { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" } ], "thesis_committee": [ { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Bouman", "given_name": "Katherine L.", "orcid": "0000-0003-0077-4367", "clpid": "Bouman-K-L" }, { "family_name": "Rudin", "given_name": "Cynthia", "orcid": "0000-0003-4283-2780", "clpid": "Rudin-Cynthia" }, { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This thesis has two main focuses: (1) surrogate modeling of elastodynamic systems, and (2) inference methods for the inexpensive characterization of elastodynamic systems. Elastodynamics is the study of how and why materials move and deform when they are subject to time-varying loads, covering a wide range of applications from architected materials, to telecommunications, seismology, sound isolation, non-destructive evaluation, and medical imaging. Here, we explore how to more efficiently model elastodynamics, and what we can infer about our environment from observing them.
\r\n\r\nThe next generation of material engineering aims to leverage advanced multi-functional control over elastodynamic behaviors, but is currently limited by the large computational cost of purely physics-based modeling methods. Surrogate models aim to alleviate this cost by providing a data-driven approach to evaluate engineered material systems more efficiently. However, most current surrogate models lack certain useful traits, diminishing their potential for real-world use. This thesis begins by surveying the current state of surrogate modeling techniques, and establishes a set of state-of-the-art traits that greatly augment the utility of surrogate models, offering a perspective for the future direction of the field.
\r\n\r\nNext, a data-driven surrogate model based on Gaussian process regression for the computation of dispersion relations is developed, GPR-dispersion. The model exhibits several of the aforementioned traits, including representation invariance, data efficiency, incorporating direct use of physical theories, and the provision of both uncertainty estimates on its predictions and gradients for compatibility with gradient-based design optimization methods. GPR-dispersion is evaluated in comparison against both deep learning and traditional physics-based models.
\r\n\r\nThe thesis then pivots to inference methods for the inexpensive characterization of material systems via partial observation of elastodynamic behaviors. Tissue stiffness is a tremendously important biomarker for a long list of health conditions, but often needs to be evaluated in a medical clinic with expensive equipment and highly trained workers. At-home health monitoring is a major next-generation goal of healthcare, but the trajectories of current consumer-grade sensor technology and biomarker inference methods have not yet fully intersected.
\r\n\r\nInspired by a related work (Visual Vibration Tomography), Visual Surface Wave Tomography (VSWT) is proposed. VSWT observes partial information about the surface waves of layered elastodynamic systems (such as biological tissue) through monocular video to infer subsurface constitutive and geometrical information. Simulated experiments are presented to evaluate the accuracy, sensitivity, and limits of the method under ideal conditions. Real-world experimental results are presented using phantom materials that emulate biological tissue to demonstrate a practical proof of concept.
", "doi": "10.7907/dcbz-sj62", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:15150", "collection": "thesis", "collection_id": "15150", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05042023-201010843", "primary_object_url": { "basename": "BrianLeeKiwonKim_Thesis.pdf", "content": "final", "filesize": 22062225, "license": "other", "mime_type": "application/pdf", "url": "/15150/1/BrianLeeKiwonKim_Thesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Dynamics of Time-Varying and Nonlinear Phononic Lattices", "author": [ { "family_name": "Kim", "given_name": "Brian Lee Kiwon", "orcid": "0000-0002-2403-8703", "clpid": "Kim-Brian-Lee-Kiwon" } ], "thesis_advisor": [ { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" } ], "thesis_committee": [ { "family_name": "Minnich", "given_name": "Austin J.", "orcid": "0000-0002-9671-9540", "clpid": "Minnich-A-J" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Chong", "given_name": "Christopher", "orcid": "0000-0002-4908-3252", "clpid": "Chong-C" }, { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The control of waves and vibrations in materials and structures underpins both the most common and the most advanced technologies. Spatially structured and periodic media have been widely studied and applied to signal processing, vibration mitigation, focusing, and other applications beyond the capabilities of bulk materials. Recently, interest has grown in the effects of temporal variation of material and medium properties on wave propagation. Temporal variations serve as an additional dimension for the design and structure of materials, further expanding potential functionalities and performance. Many of the concepts of waves in time-varying media have been developed in photonics and other electromagnetic systems, but the same fundamental dynamics govern acoustic and elastic systems, which provide alternative opportunities for implementation and new applications of time-varying media. In this thesis, we employ a one-dimensional phononic lattice composed of repelling ring magnets with electromagnetic coils that act as time-dependent grounding stiffness. The lattice provides an excellent platform for studying waves in time-varying media, with implementation and modeling of time-variation of elastic properties made simple by its discreteness. In addition, the repelling force between the magnets allows not only for the study of the linear dynamics of time-varying systems for small displacements but also for the exploration of the interaction between time-variation and nonlinear effects. We first present novel demonstrations of two types of time-varying wave phenomena in acoustic or elastic systems. First, the measurement of the propagation of waves across a temporal discontinuity in elastic properties demonstrates the temporal analog to refraction across a spatial boundary. Second, the experimental reconstruction of the dispersion relation of a time-periodic periodic medium shows the opening of wavenumber band gaps. We then characterize the dynamic stability of the time-periodic lattice and consider the role of nonlinearity. Finally, we investigate the possible existence of wavenumber gap breathers, temporally localized solutions of the discrete, nonlinear system.
", "doi": "10.7907/n7mv-eg68", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:14963", "collection": "thesis", "collection_id": "14963", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06242022-190238579", "primary_object_url": { "basename": "Moestopo_Caltech_Thesis_Final.pdf", "content": "final", "filesize": 51975787, "license": "other", "mime_type": "application/pdf", "url": "/14963/12/Moestopo_Caltech_Thesis_Final.pdf", "version": "v8.0.0" }, "type": "thesis", "title": "Design, Fabrication, and Mechanical Analysis of Intertwined and Frictional Micro-Architected Materials", "author": [ { "family_name": "Moestopo", "given_name": "Widianto Putra", "orcid": "0000-0002-7617-4280", "clpid": "Moestopo-Widianto-Putra" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Pellegrino", "given_name": "Sergio", "orcid": "0000-0001-9373-3278", "clpid": "Pellegrino-S" }, { "family_name": "Bhattacharya", "given_name": "Kaushik", "orcid": "0000-0003-2908-5469", "clpid": "Bhattacharya-K" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Natural biomaterials, e.g., shells, bone, and wood, are typically comprised of hard and soft constituent materials that are hierarchically ordered to achieve mechanical resilience, light weight, and multifunctionality. Advanced fabrication techniques have enabled the creation of precisely architected materials with exceptional mechanical properties unattainable by their constituent materials, yet they are often designed with fully interconnected structural members whose junctions are detrimental to their performance because they serve as stress concentrations for damage accumulation and lower mechanical resilience. Most studies have also focused on understanding the stretching, bending, and buckling of the structural members, while explorations toward contact interactions within structural members remain limited. We address these challenges by (i) introducing a new three-dimensional (3D) hierarchical architecture in which fibers are interwoven to construct effective beams, (ii) introducing the concept of knots into the hierarchical architecture framework, and (iii) developing a model to study the effects of structural element length scale on the energy dissipation capability of a frictional architected material.
\r\n\r\nWe first explore the effective lattice response of hierarchical woven microlattices, and we demonstrate the superior ability of woven architectures to achieve high tensile and compressive strains via smooth reconfiguration of woven microfibers in the effective beams and junctions without failure events. We study how fiber topology and constituent materials influence the mechanical behaviors of hierarchical intertwined structures, and we compare our results with theory. Our study reveals that knot topology allows a new regime of deformation capable of shape-retention, leading to increased absorbed energy and failure strain compared to structures with woven topology. Agreements between experimental results and a model for long overhand knots suggest that the model can aid the optimization of the mechanical performance of microwoven materials. We then adapt classical contact mechanics and adhesion models to explore the influence of the size of structural elements in a frictional architected material on its energy dissipation capability. Our model shows that the energy dissipation capability of our frictional architected material can be significantly increased when it is scaled down from the mm-scale to the sub-micron length scale.
\r\n\r\nOur woven hierarchical design offers a pathway to make traditionally stiff and brittle materials more deformable and introduces a new building block for 3D architected materials with complex nonlinear mechanics. The unique tightening mechanism introduced by knotted topology unlocks new ways to create shape-reconfigurable, highly extensible, and extremely energy-absorbing bulk, 3D architected materials with mechanical properties that can be tuned not only by their geometries and bulk properties, but also by the surface interactions experienced by the structural elements. Lastly, our modeling work shows the potential of creating highly dissipative architected materials with shape-retention capability via carefully architected structural elements.
", "doi": "10.7907/ycqd-1f27", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15113", "collection": "thesis", "collection_id": "15113", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03022023-175118888", "primary_object_url": { "basename": "Caltech_Thesis_KimGunho.pdf", "content": "final", "filesize": 34728792, "license": "other", "mime_type": "application/pdf", "url": "/15113/1/Caltech_Thesis_KimGunho.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Wave Propagation in Periodic Acoustic Metamaterials: from 1D to 3D", "author": [ { "family_name": "Kim", "given_name": "Gunho", "orcid": "0000-0003-1796-0908", "clpid": "Kim-Gunho" } ], "thesis_advisor": [ { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" } ], "thesis_committee": [ { "family_name": "Shapiro", "given_name": "Mikhail G.", "orcid": "0000-0002-0291-4215", "clpid": "Shapiro-M-G" }, { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Wave propagation in periodic structures has been studied for centuries; for example, Newton derived the velocity of sound based on a linear lattice. Recently, advanced manufacturing techniques have led to the fabrication of geometrically complex architected materials with acoustic properties unattainable by their constituent materials. Such rationally designed structures are often called acoustic metamaterials and they can be engineered to transmit, block, amplify, or redirect acoustic waves. Subwave-length building blocks, typically periodic (but not necessarily so), can be assembled into effectively continuous materials to manipulate dispersive properties of vibrational waves in ways that differ substantially in conventional media. This thesis investigates rationally designed acoustic metamaterials, ranging from 1D to 3D, and how acoustic wave propagation can be controlled by these artificially structured composite materials for ultrasound-related biomedical applications.
\r\n\r\nI first explore 1D wave propagation in acoustic metamaterials to study the basic mechanics and relevant analysis skills. Bio-inspired helical mechanical metamaterials are designed and their normal modes are investigated. I demonstrate the ability to vary the acoustic properties of the helical metamaterials by perturbing the geometrical structure and mass distribution. By locally adding eccentric and denser elements in the unit cells, I change the moment of inertia of the system and introduce centro-asymmetry. This allows me to control the degree of mode coupling and the width of subwavelength band gaps in the dispersion relation, which are the product of enhanced local resonance hybridization.
\r\n\r\nThen I study 2D wave propagation in microlattice acoustic metamaterials for ultra- sound manipulation. When coupled with pressure waves in the surrounding fluid, the dynamic behavior of microlattices in the long wavelength limit can be explained in the context of Biot\u2019s theory of poroelasticity. I exploit elastoacoustic wave propagation within 3D-printed polymeric microlattices to design a gradient refractive index lens for underwater wave focusing. A modified Luneburg lens index profile adapted for ultrasonic wave lensing is demonstrated via the finite element method and underwater testing, showcasing a computationally efficient poroelasticity-based design approach that enables accelerated design of acoustic wave manipulation devices.
\r\n\r\nLastly, I show that tailorable 3D wave propagation can be achieved based on the findings from the previous chapters. Functional ultrasound imaging enables sensitive, high-resolution imaging of neural activity in freely behaving animals and human patients. However, the skull acts as an aberrant and absorbing layer for sound waves, leading to most functional ultrasound experiments being conducted after skull removal. A microscale 2-photon polymerization technique is adopted to fabricate a conformal acoustic window with a high stiffness-to-density ratio and sonotransparency. Long-term biocompatibility and lasting signal sensitivity are demonstrated over a long period of time (> 4 months) by conducting ultrasound imaging in mouse models implanted with the metamaterial skull prosthesis.
", "doi": "10.7907/dyq0-vm69", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:14535", "collection": "thesis", "collection_id": "14535", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03312022-021127047", "primary_object_url": { "basename": "Peyman_Ayoubi_2022_PhD_Thesis_Submitted_To_Library_v2.pdf", "content": "final", "filesize": 33559127, "license": "other", "mime_type": "application/pdf", "url": "/14535/1/Peyman_Ayoubi_2022_PhD_Thesis_Submitted_To_Library_v2.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Modeling and Parameterization of Basin Effects for Engineering Design Applications", "author": [ { "family_name": "Ayoubi", "given_name": "Peyman", "orcid": "0000-0001-6795-4923", "clpid": "Ayoubi-Peyman" } ], "thesis_advisor": [ { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "thesis_committee": [ { "family_name": "Avouac", "given_name": "Jean-Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" }, { "family_name": "Kohler", "given_name": "Monica D.", "orcid": "0000-0002-4703-190X", "clpid": "Kohler-M-D" }, { "family_name": "Ross", "given_name": "Zachary E.", "orcid": "0000-0002-6343-8400", "clpid": "Ross-Z-E" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The term \"Basin effects\" refers to trapped and reverberating earthquake waves in soft sedimentary deposits overlying convex depressions of the basement bedrock, which significantly alter the frequency content, amplitude, and duration of seismic waves. This has played an important role in shaking duration and intensity in past earthquakes such as the Mw 8.0 1985 Micho\u00e1can, Mexico, Mw 6.9 1995 Kobe, Japan, and Mw 7.8 2015 Gorkha, Nepal earthquakes. While the standard practice is to perform a 1D analysis of a soil column, edge-effect and surface waves are among the key contributors to the surface ground motion within a basin. This thesis studies basin effects in a 2D medium to help better understand the phenomena, better parameterize them, and suggest a path to appropriately incorporate them in ground motion prediction equations and building design codes. After the introduction in Chapter 1, I present the results in three main parts as follows:
\r\n\r\nIn Chapter 2, we perform an extensive parametric study on the characteristics of surface ground motion associated with basin effects. We use an elastic idealized-shaped medium subjected to vertically propagating SV plane waves and examine the effects of basin geometry and material properties. We specifically study the effects of four dimensionless parameters, the width-to-depth (aspect) ratio, the rock-to-soil material contrast, a dimensionless frequency that quantifies the depth of the basin relative to the dominant incident wavelength, and a dimensionless distance that quantifies the distance of the basin edges relative to the dominant wavelength. Our results show that basin effects can be reasonably characterized using at least three independent parameters, each of which can significantly alter the resultant ground motion. To demonstrate the application of dimensional analysis applied here, we investigate the response of the Kathmandu Valley during the 2015 Mw 7.8 Gorkha Earthquake in Nepal using an idealized basin geometry and soil properties. Our results show that a simplified model can capture notable ground motion characteristics associated with basin effects.
\r\n\r\nChapter 3 uses the identified parameters from the previous chapter to estimate surface acceleration time-series given earthquake frequency content, basin geometry and material properties, and location inside a basin. This is of practical use when the amount of available data is limited or the fast estimation of time-series is desirable. For that, we train a neural network to estimate surface ground acceleration time-series across a basin. Three input parameters are needed for the estimation: basin-to-bedrock shear wave velocity ratio, aspect ratio of the basin, and dimensionless location. These parameters define an idealized-shaped basin and the location at which the time-series are to be computed. It will be shown that the model performs with high accuracy in comparison to the result of a full-fidelity Finite Element (FE) simulation (ground truth) and generalizes reasonably well for input parameters outside of the training set. Moreover, we will also use the model for the case of Kathmandu Valley, Nepal during the 2015 Mw 7.8 Gorkha earthquake and compare the results of NN versus recordings of the mainshock, similarly to Chapter 2.
\r\n\r\nOnce we have studied basin behavior in a homogeneous case in previous chapters, we focus on material representation inside a basin in Chapter 4. Here, we study basin effects for the cases where high-frequency response and realistic material representation are desirable. However, the lack of sufficient information about the material properties and stratigraphy of a basin prevents accurate simulation of the phenomena. To do that, we perform a stochastic analysis using the Monte Carlo technique, where a random field represents basin material. Similarly to the previous chapters, we use a 2D FE model with an idealized basin subjected to vertically propagating SV plane waves and investigate the spatial variation of surface ground motion (SGM) associated with basin effects by assuming different realizations of the correlated random field. We then study various correlation lengths, coefficients of variations, and autocorrelation functions to evaluate their contribution to SGM. We show that the coefficient of variation is the most influential parameter on SGM, followed by correlation lengths and type of autocorrelation function. Increasing the coefficient of variation not only affects the mean surface amplification, but also results in a dramatic change in the standard deviation. Correlation lengths and autocorrelation functions, on the other hand, are of less importance for the cases we examine in this study.
", "doi": "10.7907/4e61-q346", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14019", "collection": "thesis", "collection_id": "14019", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12092020-002934412", "primary_object_url": { "basename": "kusanovic_danilo_2021_thesis.pdf", "content": "final", "filesize": 9676088, "license": "other", "mime_type": "application/pdf", "url": "/14019/1/kusanovic_danilo_2021_thesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Improving Reduced Order Models of Soil-Structure Interaction Using an Ensemble Kalman Inversion Finite Element Model Updating Framework", "author": [ { "family_name": "Kusanovic", "given_name": "Danilo Smiljan", "orcid": "0000-0002-0935-2577", "clpid": "Kusanovic-Danilo-Smiljan" } ], "thesis_advisor": [ { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "thesis_committee": [ { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" }, { "family_name": "Stuart", "given_name": "Andrew M.", "orcid": "0000-0001-9091-7266", "clpid": "Stuart-A-M" }, { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "In civil engineering, almost all structures are somehow in contact with soil - i.e., have foundations or support elements that either rest on or are embedded in soil. Thus, their seismic response is governed by the interaction between the structure, the non-structural components, the foundation, and the surrounding soil. Predicting such interaction becomes increasingly complex when uncertainties of soil and structural material, ground motion variability, and dissipation mechanisms are considered. The accuracy of numerical models to predict the linear or nonlinear responses of structures depends not only on how well the uncertainties in the material properties and input motion are estimated, but also on how well the various sources of energy dissipation and their interaction are modeled. Therefore, high-fidelity simulation of soil-structure interaction (SSI) problems require advanced models that can capture the nonlinear behavior of soils and structures, and parallel computing capabilities to optimize the cost associated with large scale problems. In spite of this fact, SSI in practice is widely accounted for using fixed-base building and reduced-order-models (ROM) which usually trade accurate solution for fast ones. Unfortunately, if SSI effects are neglected or poorly estimated, then critical response measures of a structure can be over- or under-estimated, which in turn can lead to unsafe or overly\r\nconservative designs.
\r\n\r\nMotivated by the previous challenge, in this thesis work we present a robust and efficient framework for finite element model (FEM) updating based on ensemble-Kalman inversion (EnKI). The EnKI-FEM updating framework is used to obtain suitable parameters to inform a ROM from data generated using high-fidelity FEM simulations. Since high-fidelity SSI simulations call for accurate and computationally efficient capabilities, as a part of this work, we developed Seismo-VLAB, a simple, fast, and extendable C++ finite element software to optimize large-scale simulations of dynamic and nonlinear SSI problems. The EnKI-FEM updating framework is thus integrated in Seismo-VLAB allowing to identify any parameter of the ROM without compromising accuracy. The so-generated ROM are finally employed to propose a new dimensionless frequency mapping to estimate the soil impedance for time domain analysis and to investigate soil-structure-interaction effects at a regional-scale. The presented methodology is general enough and it can be extended to more complex structural and/or geotechnical systems, allowing to construct highly-accurate ROM in a simple manner.
", "doi": "10.7907/m2qj-s182", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:13992", "collection": "thesis", "collection_id": "13992", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11052020-043034327", "type": "thesis", "title": "Identification of Structural Damage, Ground Motion Response, and the Benefits of Dense Seismic Instrumentation", "author": [ { "family_name": "Filippitzis", "given_name": "Filippos", "orcid": "0000-0001-8377-4914", "clpid": "Filippitzis-Filippos" } ], "thesis_advisor": [ { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" }, { "family_name": "Kohler", "given_name": "Monica D.", "orcid": "0000-0002-4703-190X", "clpid": "Kohler-M-D" } ], "thesis_committee": [ { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" }, { "family_name": "Kohler", "given_name": "Monica D.", "orcid": "0000-0002-4703-190X", "clpid": "Kohler-M-D" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This study explores the problems of identifying structural damage in steel frame buildings, through the use of dense instrumentation over the height of the building, and of characterizing the ground motion response in urban Los Angeles following the 2019 Ridgecrest earthquakes, through the use of dense instrumentation from available seismic networks, including the very dense Community Seismic Network.
\r\n\r\nFirst we explore the possibility of tracing possible nonlinear behavior of a structure by updating an equivalent linear system model in short time segments of the earthquake-induced excitation and response time histories, using a moving time window approach. The stiffness and damping related parameters of the equivalent linear model are estimated by minimizing a measure of fit between the measured and model predicted response time histories for each time window. We explore the effectiveness of the methodology for two example applications, a single-story and a six-story steel moment frame building. For the single-story building, the methodology is shown to be very effective in tracing the nonlinearities, while the six-story building is designed to also reveal the limitations of the methodology, mainly arising from the different types of model errors manifested in the formulation.
\r\n\r\nNext, we investigate the problem of structural damage identification through the use of sparse Bayesian learning (SBL) techniques. This is based on the premise that damage in a structure appears only in a limited number of locations. SBL methods that had been previously applied for structural damage identification used measurements related to modal properties and were thus limited to linear models. Here we present a methodology that allows for the application of SBL in non-linear models, using time history measurements recorded from a dense network of sensors installed along the building height. We develop a two-step optimization algorithm in which the most probable values of the structural model parameters and the hyper-parameters are iteratively obtained. An equivalent single-objective minimization problem that results in the most probable model parameter values is also derived. We consider the example problem of identifying damage in the form of weld fractures in a 15-story moment resisting steel frame building, using a nonlinear finite element model and simulated acceleration data. Fiber elements and a bilinear material model are used in order to account for the change of local stiffness when cracks at the welds are subjected to tension and the model parameters characterize the loss of stiffness as the crack opens under tension. The damage identification results demonstrate the effectiveness and robustness of the proposed methodology in identifying the existence, location, and severity of damage for a variety of different damage scenarios, and degrees of model and measurement errors. The results show the great promise of the SBL methodology for damage identification by integrating nonlinear finite element models and response time history measurements.
\r\n\r\nThe final part of the thesis involves studying the ground motion response in urban Los Angeles during the two largest events (M7.1 and M6.4) of the 2019 Ridgecrest earthquake sequence using recordings from multiple regional seismic networks as well as a subset of 350 stations from the much denser Community Seismic Network. The response spectral (pseudo) accelerations for a selection of periods of engineering significance are calculated. Significant spectral acceleration amplification is present and reproducible between the two events. For the longer periods, coherent spectral acceleration patterns are visible throughout the Los Angeles Basin, while for the shorter periods, the motions are less spatially coherent. The dense Community Seismic Network instrumentation allows us to observe smaller-scale coherence even for these shorter periods. Examining possible correlations of the computed response spectral accelerations with basement depth and Vs30, we find the correlations to be stronger for the longer periods. Furthermore, we study the performance of two state-of-the-art methods for estimating ground motions for the largest event of the Ridgecrest earthquake sequence, namely 3D finite difference simulations and ground motion prediction equations. For the simulations, we are interested in the performance of the two Southern California Earthquake Center 3D Community Velocity Models (CVM-S and CVM-H). For the ground motion prediction equations, we consider four of the 2014 Next Generation Attenuation-West2 Project equations. For some cases, the methods match the observations reasonably well; however, neither approach is able to reproduce the specific locations of the maximum response spectral accelerations, or match the details of the observed amplification patterns.
", "doi": "10.7907/x0sf-pq18", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:13998", "collection": "thesis", "collection_id": "13998", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11112020-213135157", "type": "thesis", "title": "Matching Waveform Envelopes for Earthquake Early Warning", "author": [ { "family_name": "Roh", "given_name": "Becky", "orcid": "0000-0002-3905-0086", "clpid": "Roh-Becky" } ], "thesis_advisor": [ { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" } ], "thesis_committee": [ { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" }, { "family_name": "Hall", "given_name": "John F.", "orcid": "0000-0002-7863-5060", "clpid": "Hall-J-F" }, { "family_name": "Ross", "given_name": "Zachary E.", "orcid": "0000-0002-6343-8400", "clpid": "Ross-Z-E" }, { "family_name": "Allen", "given_name": "Richard Harvey", "orcid": "0000-0003-4293-9772", "clpid": "Allen-Richard-Harvey" }, { "family_name": "Minson", "given_name": "Sarah", "orcid": "0000-0001-5869-3477", "clpid": "Minson-Sarah" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Current earthquake early warning (EEW) algorithms are continuously optimized to strive for fast, accurate source parameter estimates for the rupturing earthquake (i.e. magnitude, location), which are then used to predict ground motions expected at a site. However, they may still struggle with challenging cases, such as offshore events and complex sequences. An envelope-based two-part search algorithm is developed to handle such cases. This algorithm matches different templates to the incoming observed ground motion envelopes to find the optimal earthquake source parameter estimates.
\r\n\r\nThe algorithm consists of two methods. Method I is the standard grid search, and it uses Cua-Heaton ground motion envelopes as its templates; Method II is the extended catalog search, and its templates are waveform envelopes from past real and synthetic earthquakes. The grid search is intended for robustness and provides approximate average solutions, whereas the extended catalog search matches envelopes considering the station\u2019s specific site and path effects. In parallel execution, Methods I and II work together \u2013 either by confirming each other\u2019s solutions or accepting the solution with stronger fits \u2013 to provide the best parameter estimates based on waveform-based data.
\r\n\r\nThe main advantage of the two-part search algorithm is its ability to find parameter estimates of reduced uncertainties using the P-wave data from a single station. Many algorithms wait until multiple stations are triggered to reduce tradeoffs between the magnitude and location. This waiting time, however, is detrimental in EEW, for it jeopardizes the warning time that can be issued to nearby regions expected to experience strong shaking. The use of a single station would virtually eliminate this waiting time, maximizing the warning time without the cost in accuracy of the estimates.
\r\n\r\nBecause EEW is a race against time, further actions are taken for more rapid estimation of the earthquake source parameters. A Bayesian approach using prior information has the potential to reduce uncertainties that arise in the initial time points due to tradeoffs between the magnitude and location. This essentially increases the confidence of the initial parameter estimates, allowing alerts to be issued faster. A KD tree nearest neighbor search is also introduced to reduce latency in the time it takes to find the best-fitting solutions. In comparison to an exhaustive, brute-force search, it cuts the searching time by only examining through a fraction of the total database.
\r\n\r\nAn envelope-based algorithm examines the shape and relative frequency content and makes appropriate judgments, just as a human seismologist would; it also addresses the issue of data transmission latencies. Overall, this algorithm is able to interpret the complexity of earthquakes and assess the features they hold to ultimately communicate information of significant ground shaking to different regions.
", "doi": "10.7907/hw8k-zx98", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:14019", "collection": "thesis", "collection_id": "14019", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12092020-002934412", "primary_object_url": { "basename": "kusanovic_danilo_2021_thesis.pdf", "content": "final", "filesize": 9676088, "license": "other", "mime_type": "application/pdf", "url": "/14019/1/kusanovic_danilo_2021_thesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Improving Reduced Order Models of Soil-Structure Interaction Using an Ensemble Kalman Inversion Finite Element Model Updating Framework", "author": [ { "family_name": "Kusanovic", "given_name": "Danilo Smiljan", "orcid": "0000-0002-0935-2577", "clpid": "Kusanovic-Danilo-Smiljan" } ], "thesis_advisor": [ { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "thesis_committee": [ { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" }, { "family_name": "Stuart", "given_name": "Andrew M.", "orcid": "0000-0001-9091-7266", "clpid": "Stuart-A-M" }, { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "In civil engineering, almost all structures are somehow in contact with soil - i.e., have foundations or support elements that either rest on or are embedded in soil. Thus, their seismic response is governed by the interaction between the structure, the non-structural components, the foundation, and the surrounding soil. Predicting such interaction becomes increasingly complex when uncertainties of soil and structural material, ground motion variability, and dissipation mechanisms are considered. The accuracy of numerical models to predict the linear or nonlinear responses of structures depends not only on how well the uncertainties in the material properties and input motion are estimated, but also on how well the various sources of energy dissipation and their interaction are modeled. Therefore, high-fidelity simulation of soil-structure interaction (SSI) problems require advanced models that can capture the nonlinear behavior of soils and structures, and parallel computing capabilities to optimize the cost associated with large scale problems. In spite of this fact, SSI in practice is widely accounted for using fixed-base building and reduced-order-models (ROM) which usually trade accurate solution for fast ones. Unfortunately, if SSI effects are neglected or poorly estimated, then critical response measures of a structure can be over- or under-estimated, which in turn can lead to unsafe or overly\r\nconservative designs.
\r\n\r\nMotivated by the previous challenge, in this thesis work we present a robust and efficient framework for finite element model (FEM) updating based on ensemble-Kalman inversion (EnKI). The EnKI-FEM updating framework is used to obtain suitable parameters to inform a ROM from data generated using high-fidelity FEM simulations. Since high-fidelity SSI simulations call for accurate and computationally efficient capabilities, as a part of this work, we developed Seismo-VLAB, a simple, fast, and extendable C++ finite element software to optimize large-scale simulations of dynamic and nonlinear SSI problems. The EnKI-FEM updating framework is thus integrated in Seismo-VLAB allowing to identify any parameter of the ROM without compromising accuracy. The so-generated ROM are finally employed to propose a new dimensionless frequency mapping to estimate the soil impedance for time domain analysis and to investigate soil-structure-interaction effects at a regional-scale. The presented methodology is general enough and it can be extended to more complex structural and/or geotechnical systems, allowing to construct highly-accurate ROM in a simple manner.
", "doi": "10.7907/m2qj-s182", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:13762", "collection": "thesis", "collection_id": "13762", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012020-154218098", "primary_object_url": { "basename": "Kien_Nguyen_2020_PhD_Thesis.pdf", "content": "final", "filesize": 9921236, "license": "other", "mime_type": "application/pdf", "url": "/13762/1/Kien_Nguyen_2020_PhD_Thesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Reduced-Order Model for Dynamic Soil-Pipe Interaction Analysis", "author": [ { "family_name": "Nguyen", "given_name": "Kien Trung", "orcid": "0000-0001-5761-3156", "clpid": "Nguyen-Kien-Trung" } ], "thesis_advisor": [ { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "thesis_committee": [ { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" }, { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" }, { "family_name": "Hall", "given_name": "John F.", "orcid": "0000-0002-7863-5060", "clpid": "Hall-J-F" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Pipelines are very vulnerable infrastructure components to geohazard-induced ground deformation and failure. How soil transmits loads on pipelines and vice versa, known as soil-pipe interaction (SPI), thus is very important for the assessment and design of resilient pipeline systems.
\r\n\r\nIn the first part, this work proposes a simplified macroelement designed to capture SPI in cohesionless soils subjected to arbitrary loading normal to the pipeline axis. We present the development of a uniaxial hysteresis model that can capture the smooth nonlinear reaction force-relative displacement curves (FDCs) of SPI problems. Using the unscented Kalman filter, we derived the model parameter κ that controls the smoothness of the transition zone from linear to plastic using published experimental data. We extended this uniaxial model to biaxial loading effects and showed that the macroelement can capture effects such as pinching and shear-dilation coupling. The model input parameters were calibrated using finite element (FE) analyses validated by experiments. The FDCs of the biaxial model were verified by comparison with FE and smoothed-particle hydrodynamic (SPH) simulations for different loading patterns: cyclic uniaxial, 0-shaped, 8-shaped, and transient loading. Accounting for smooth nonlinearity, hysteresis, pinching, and coupling effects, the proposed biaxial macroelement shows good agreement with FE and SPH analyses, while maintaining the computational efficiency and simplicity of beam-on-nonlinear-Winkler foundation models, as well as a small number of input parameters.
\r\n\r\nNext, this work presents analytical solutions for computing frequency-domain axial and in-plane soil impedance functions (SIFs) for an infinitely long rigid circular structure buried horizontally in homogeneous elastic half-space. Using Hankel— and Bessel—Fourier series expansion, we solved a mixed-boundary-value problem considering a harmonic displacement at the structure boundary and traction-free boundary condition at the half-space free surface. We then verified our analytical solutions using results obtained from FE simulations. The SIFs of a buried structure in a homogeneous elastic half-space calculated by these two approaches are in perfect agreement with each other. In addition, we used analytical solutions and FE simulations to comprehensively investigate factors that affect the SIFs in homogeneous and two-layered half-spaces, respectively. The parametric study shows that SIFs of buried structures in elastic half-space primarily depend on frequency of excitation, shear modulus and Poisson's ratio of the half-space, burial depth and radius of the structure. In a two-layered soil domain, SIFs depend also on material contrast and the distance from the structure location to the interface between soil layers.
\r\n\r\nLastly, it demonstrates how the SIFs obtained previously can be incorporated into a reduced-order model to analyze SPI problems, specifically a straight pipe subjected to Rayleigh surface wave propagating through homogeneous and heterogeneous elastic half-spaces. Calculated displacement time histories at the control points are shown to agree well with those computed by direct two-dimensional FE analyses.
", "doi": "10.7907/mekk-dc25", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13587", "collection": "thesis", "collection_id": "13587", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11212019-100323260", "type": "thesis", "title": "Application of Path-Independent Integrals to Soil-Structure Interaction", "author": [ { "family_name": "Garc\u00eda Su\u00e1rez", "given_name": "Antonio Joaqu\u00edn", "orcid": "0000-0001-8830-4348", "clpid": "Garc\u00eda-Su\u00e1rez-Antonio-Joaqu\u00edn" } ], "thesis_advisor": [ { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Ortiz", "given_name": "Michael", "orcid": "0000-0001-5877-4824", "clpid": "Ortiz-M" }, { "family_name": "Meiron", "given_name": "Daniel I.", "orcid": "0000-0003-0397-3775", "clpid": "Meiron-D-I" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "Assessing seismic pressure increment on buried structures is a critical step in the design of infrastructure in earthquake-prone areas. Due to intrinsic complexities derived from the need to match the solution in the far-field to the localized solution around the structure, the near-field, researchers have aimed at finding simplified models focused on engineering variables as the seismic earth thrust. One such model is the so-called Younan-Veletsos model, which pivots on a stringent assumption on the stress tensor.
\r\n\r\nAt the same time, the might of the path-independent integrals of solid mechanics to deal with problems in Geotechnical Engineering at large, and Soil-Structure Interaction in particular, has remained unexplored, despite of a rich landscape of potential applications. The unbridled success of these path-independent integrals in Fracture Mechanics, a discipline which cannot be understood without them currently, may be mirrored in problems in Geotechnical Engineering, since the two fields, despite appearing very detached from each other at first glance, share deep traits: in both cases, the system under consideration can be conceptualized as a domain with simple, easy-to-assess regions (the areas where remote loading is applied and the far-field, respectively) and also with other complex, hard-to-understand regions (the crack tip, the near-field).
\r\n\r\nWe present the first derivation of the exact solution of the Younan-Veletsos problem, which is later analyzed to reveal phenomena not captured by previous approximate solutions. Then, we introduce a novel model which relies on the path-independent Rice\u2019s J-integral, a customary tool in Fracture Mechanics, which is applied here in the Soil-structure Interaction context for the first time. This novel model captures those features of the exact solution that were missed by prior approximations. The capabilities of the J-integral to, first, find an upper bound of the force induced by earthquakes over the walls of underground structures, under some conditions, and, second, to understand the soil-structure kinematic interaction phenomenon are also assessed.
\r\n\r\nAdditionally, the intermediate step of analyzing of the far-field yielded some results concerning Site Response Analysis which are also included in the text.
", "doi": "10.7907/MMWW-B046", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13628", "collection": "thesis", "collection_id": "13628", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01202020-210729635", "type": "thesis", "title": "High-Cycle Dynamic Cell Fatigue with Applications on Oncotripsy", "author": [ { "family_name": "Figueroa-Schibber", "given_name": "Erika", "orcid": "0000-00002-6629-297X", "clpid": "Figueroa-Schibber-Erika" } ], "thesis_advisor": [ { "family_name": "Ortiz", "given_name": "Michael", "orcid": "0000-0001-5877-4824", "clpid": "Ortiz-M" } ], "thesis_committee": [ { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Ortiz", "given_name": "Michael", "orcid": "0000-0001-5877-4824", "clpid": "Ortiz-M" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "The method of oncotripsy (from Greek, onco- meaning \"tumor\" and \u2013tripsy \"to break\") exploits aberrations in the material properties and morphology of cancerous cells to target them selectively using tuned low-intensity pulsed ultrasound. Compared to other noninvasive ultrasound treatments that ablate malignant tissue, oncotripsy has the capability of targeting unhealthy tissue with minimal damage to healthy cells in the ablation process.
\r\n\r\nWe propose a model of oncotripsy that follows as an application of cell dynamics, statistical mechanical theory of network elasticity and 'birth-death' kinetics to describe processes of damage and repair of the cytoskeleton. We also develop a reduced dynamical model that approximates the three-dimensional dynamics of the cell and facilitates parameter studies, including sensitivity analysis and process optimization.
\r\n\r\nThe dynamical system encompasses the relative motion of the nucleus to the cell membrane and a state variable measuring the extent of damage to the cytoskeleton. The dynamical system evolves in time as a result of structural dynamics and kinetics of cytoskeletal damage and repair. The resulting dynamics are complex and exhibits behavior on multiple time scales, including the period of vibration and attenuation, the characteristic time of cytoskeletal healing, the pulsing period and the time of exposure to the ultrasound. Damage on the cells develops in the order of millions of ultrasound cycles, and the failure mechanism is explained as a fatigue process. We also account for cell variability and estimate the attendant variance of the time-to-death of a cell population. We show that the dynamical model predicts \u2014 and provides a conceptual basis for understanding \u2014 the oncotripsy effect and other trends observed in experiments.
", "doi": "10.7907/0425-SN62", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13762", "collection": "thesis", "collection_id": "13762", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012020-154218098", "primary_object_url": { "basename": "Kien_Nguyen_2020_PhD_Thesis.pdf", "content": "final", "filesize": 9921236, "license": "other", "mime_type": "application/pdf", "url": "/13762/1/Kien_Nguyen_2020_PhD_Thesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Reduced-Order Model for Dynamic Soil-Pipe Interaction Analysis", "author": [ { "family_name": "Nguyen", "given_name": "Kien Trung", "orcid": "0000-0001-5761-3156", "clpid": "Nguyen-Kien-Trung" } ], "thesis_advisor": [ { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "thesis_committee": [ { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" }, { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" }, { "family_name": "Hall", "given_name": "John F.", "orcid": "0000-0002-7863-5060", "clpid": "Hall-J-F" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Pipelines are very vulnerable infrastructure components to geohazard-induced ground deformation and failure. How soil transmits loads on pipelines and vice versa, known as soil-pipe interaction (SPI), thus is very important for the assessment and design of resilient pipeline systems.
\r\n\r\nIn the first part, this work proposes a simplified macroelement designed to capture SPI in cohesionless soils subjected to arbitrary loading normal to the pipeline axis. We present the development of a uniaxial hysteresis model that can capture the smooth nonlinear reaction force-relative displacement curves (FDCs) of SPI problems. Using the unscented Kalman filter, we derived the model parameter κ that controls the smoothness of the transition zone from linear to plastic using published experimental data. We extended this uniaxial model to biaxial loading effects and showed that the macroelement can capture effects such as pinching and shear-dilation coupling. The model input parameters were calibrated using finite element (FE) analyses validated by experiments. The FDCs of the biaxial model were verified by comparison with FE and smoothed-particle hydrodynamic (SPH) simulations for different loading patterns: cyclic uniaxial, 0-shaped, 8-shaped, and transient loading. Accounting for smooth nonlinearity, hysteresis, pinching, and coupling effects, the proposed biaxial macroelement shows good agreement with FE and SPH analyses, while maintaining the computational efficiency and simplicity of beam-on-nonlinear-Winkler foundation models, as well as a small number of input parameters.
\r\n\r\nNext, this work presents analytical solutions for computing frequency-domain axial and in-plane soil impedance functions (SIFs) for an infinitely long rigid circular structure buried horizontally in homogeneous elastic half-space. Using Hankel— and Bessel—Fourier series expansion, we solved a mixed-boundary-value problem considering a harmonic displacement at the structure boundary and traction-free boundary condition at the half-space free surface. We then verified our analytical solutions using results obtained from FE simulations. The SIFs of a buried structure in a homogeneous elastic half-space calculated by these two approaches are in perfect agreement with each other. In addition, we used analytical solutions and FE simulations to comprehensively investigate factors that affect the SIFs in homogeneous and two-layered half-spaces, respectively. The parametric study shows that SIFs of buried structures in elastic half-space primarily depend on frequency of excitation, shear modulus and Poisson's ratio of the half-space, burial depth and radius of the structure. In a two-layered soil domain, SIFs depend also on material contrast and the distance from the structure location to the interface between soil layers.
\r\n\r\nLastly, it demonstrates how the SIFs obtained previously can be incorporated into a reduced-order model to analyze SPI problems, specifically a straight pipe subjected to Rayleigh surface wave propagating through homogeneous and heterogeneous elastic half-spaces. Calculated displacement time histories at the control points are shown to agree well with those computed by direct two-dimensional FE analyses.
", "doi": "10.7907/mekk-dc25", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:11571", "collection": "thesis", "collection_id": "11571", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302019-150220368", "type": "thesis", "title": "Improving Site Response Analysis for Earthquake Ground Motion Modeling", "author": [ { "family_name": "Shi", "given_name": "Jian", "orcid": "0000-0002-1969-7579", "clpid": "Shi-Jian" } ], "thesis_advisor": [ { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "thesis_committee": [ { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" }, { "family_name": "Graves", "given_name": "Robert W.", "clpid": "Graves-R-W" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The modeling of earthquake-induced ground motions plays an important role in the quantification of seismic hazards, which contributes to the ultimate goal of saving lives and reducing economic loss. Site response is a natural phenomenon in which soils in the earth\u2019s shallow crust alter the amplitude, frequency content, and duration of earthquake-induced ground motions. Therefore, improvements in the research of site response directly contribute to ground motion modeling, and eventually to seismic hazard quantification.
\r\n\r\nThis thesis presents two models that advance the current research in site response.
\r\n\r\nThe first model provides a tool to predict near-surface shear-wave velocity profiles from Vs30 (a proxy that represents the general stiffness of a site). This model bridges the gap between the lack of information about near-surface soil properties and the need to model site response on a regional scale (city, county, or above).
\r\n\r\nThe second model is a stress-strain model for describing 1D shearing behaviors of soils. It is capable of capturing both the small-strain and the large-strain behaviors, which makes it suitable for modeling very strong ground motions. More importantly, this model enables seismologists to construct stress-strain curves from only shear-wave velocity information, again improving our ability to model site response on a regional scale. Our validation study shows that this model outperforms the prevalent stress-strain model (namely, the MKZ model) by a considerable margin.
\r\n\r\nLastly, we demonstrate how the two models above can improve earthquake ground motion modeling: we develop an improved version of site factors for the Western United States. These site factors are provided as Fourier spectral ratios, and phase factors are provided for the first time, which enables the time delay of earthquake waves to be modeled. They can be used for incorporating site response in earthquake ground motion simulations, as well as for improving seismic hazard maps for the Western United States.
", "doi": "10.7907/X5NZ-DQ21", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:11541", "collection": "thesis", "collection_id": "11541", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05242019-115317802", "primary_object_url": { "basename": "Phlipot_Gregory_2019.pdf", "content": "final", "filesize": 86570209, "license": "other", "mime_type": "application/pdf", "url": "/11541/1/Phlipot_Gregory_2019.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "A Fully-Nonlocal Quasicontinuum Method to Model the Nonlinear Response of Periodic Truss Lattices", "author": [ { "family_name": "Phlipot", "given_name": "Gregory Paul", "orcid": "0000-0003-2721-8678", "clpid": "Phlipot-Gregory-Paul" } ], "thesis_advisor": [ { "family_name": "Kochmann", "given_name": "Dennis M.", "orcid": "0000-0002-9112-6615", "clpid": "Kochmann-D-M" } ], "thesis_committee": [ { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" }, { "family_name": "Ortiz", "given_name": "Michael", "orcid": "0000-0001-5877-4824", "clpid": "Ortiz-M" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "orcid": "0000-0002-9112-6615", "clpid": "Kochmann-D-M" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "We present a framework for the efficient, yet accurate description of general periodic truss networks based on concepts of the quasicontinuum (QC) method. Previous research in coarse-grained truss models has focused either on simple bar trusses or on two-dimensional beam lattices undergoing small deformations. Here, we extend the truss QC methodology to nonlinear deformations, general periodic beam lattices, and three dimensions. We introduce geometric nonlinearity into the model by using a corotational beam description at the level of individual truss members. Coarse-graining is achieved by the introduction of representative unit cells and a polynomial interpolation analogous to traditional QC. General periodic lattices defined by the periodic assembly of a single unit cell are modeled by retaining all unique degrees of freedom of the unit cell (identified by a lattice decomposition into simple Bravais lattices) at each macroscopic point in the simulation, and interpolating each degree of freedom individually. We show that this interpolation scheme accurately captures the homogenized properties of periodic truss lattices for uniform deformations. In order to showcase the efficiency and accuracy of the method, we compare coarse-grained simulations to fully-resolved simulations for various test problems, including: brittle fracture toughness prediction, static and dynamic indentation with geometric and material nonlinearities, and uniaxial tension of a truss lattice plate with a cylindrical hole. We also discover the notion of stretch locking --- a phenomenon where certain lattice topologies are over-constrained, resulting in artificially stiff behavior similar to volumetric locking in finite elements --- and show that using higher-order interpolation instead of affine interpolation significantly reduces the error in the presence of stretch locking in 2D and 3D. Overall, the new technique shows convincing agreement with exact, discrete results for a wide variety of lattice architectures, and offers opportunities to reduce computational expenses in structural lattice simulations and thus to efficiently extract the effective mechanical performance of discrete networks.", "doi": "10.7907/3MPP-Q119", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:11571", "collection": "thesis", "collection_id": "11571", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302019-150220368", "type": "thesis", "title": "Improving Site Response Analysis for Earthquake Ground Motion Modeling", "author": [ { "family_name": "Shi", "given_name": "Jian", "orcid": "0000-0002-1969-7579", "clpid": "Shi-Jian" } ], "thesis_advisor": [ { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "thesis_committee": [ { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" }, { "family_name": "Graves", "given_name": "Robert W.", "clpid": "Graves-R-W" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The modeling of earthquake-induced ground motions plays an important role in the quantification of seismic hazards, which contributes to the ultimate goal of saving lives and reducing economic loss. Site response is a natural phenomenon in which soils in the earth\u2019s shallow crust alter the amplitude, frequency content, and duration of earthquake-induced ground motions. Therefore, improvements in the research of site response directly contribute to ground motion modeling, and eventually to seismic hazard quantification.
\r\n\r\nThis thesis presents two models that advance the current research in site response.
\r\n\r\nThe first model provides a tool to predict near-surface shear-wave velocity profiles from Vs30 (a proxy that represents the general stiffness of a site). This model bridges the gap between the lack of information about near-surface soil properties and the need to model site response on a regional scale (city, county, or above).
\r\n\r\nThe second model is a stress-strain model for describing 1D shearing behaviors of soils. It is capable of capturing both the small-strain and the large-strain behaviors, which makes it suitable for modeling very strong ground motions. More importantly, this model enables seismologists to construct stress-strain curves from only shear-wave velocity information, again improving our ability to model site response on a regional scale. Our validation study shows that this model outperforms the prevalent stress-strain model (namely, the MKZ model) by a considerable margin.
\r\n\r\nLastly, we demonstrate how the two models above can improve earthquake ground motion modeling: we develop an improved version of site factors for the Western United States. These site factors are provided as Fourier spectral ratios, and phase factors are provided for the first time, which enables the time delay of earthquake waves to be modeled. They can be used for incorporating site response in earthquake ground motion simulations, as well as for improving seismic hazard maps for the Western United States.
", "doi": "10.7907/X5NZ-DQ21", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:10431", "collection": "thesis", "collection_id": "10431", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09122017-092017294", "type": "thesis", "title": "Data Driven Computing", "author": [ { "family_name": "Kirchdoerfer", "given_name": "Trenton Thomas", "orcid": "0000-0003-2290-1857", "clpid": "Kirchdoerfer-Trenton-Thomas" } ], "thesis_advisor": [ { "family_name": "Ortiz", "given_name": "Michael", "orcid": "0000-0001-5877-4824", "clpid": "Ortiz-M" } ], "thesis_committee": [ { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "orcid": "0000-0002-9112-6615", "clpid": "Kochmann-D-M" }, { "family_name": "Ortiz", "given_name": "Michael", "orcid": "0000-0001-5877-4824", "clpid": "Ortiz-M" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "Data Driven Computing is a new field of computational analysis which uses provided data to directly produce predictive outcomes. This thesis first establishes definitions of Data-Driven solvers and working examples of static mechanics problems to demonstrate efficacy. Significant extensions are then explored to both accommodate noisy data sets and apply the deveoloped methods to dynamic problems within mechanics. Possible method improvements discuss incorporation of data quality metrics and adaptive data sampling, while new applications focus on multi-scale analysis and the need for public databases to support constitutive data collaboration.\r\n", "doi": "10.7907/Z9Z899MV", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10451", "collection": "thesis", "collection_id": "10451", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09242017-121200052", "type": "thesis", "title": "Reducing Latencies in Earthquake Early Warning", "author": [ { "family_name": "Yin", "given_name": "Lucy", "orcid": "0000-0002-0652-9330", "clpid": "Yin-Lucy" } ], "thesis_advisor": [ { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" } ], "thesis_committee": [ { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" }, { "family_name": "Yue", "given_name": "Yisong", "orcid": "0000-0001-9127-1989", "clpid": "Yue-Yisong" }, { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" }, { "family_name": "Page", "given_name": "Morgan", "clpid": "Page-Morgan" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Existing Earthquake Early Warning (EEW) algorithms use waveform analysis for earthquake detections, estimation of source parameters (i.e., magnitude and hypocenter location), and prediction of peak ground motions at sites near the source. The latency of warning delivery due to data collection significantly restricts the usefulness of the system, especially for users in the vicinity of the earthquake source, as the warning may not arrive before the strong shaking. This presentation discusses several methods to reduce the warning latency, while maintaining reliability and robustness, so that the warning time can be maximized for users to take appropriate actions to reduce causalities and economic losses.
\r\n\r\nFirstly, we incorporated the seismicity forecast information from Epidemic-Type Aftershock Sequence (ETAS) model into EEW as prior information, under the Bayesian probabilistic inference framework. Similar to human\u2019s decision-making process, the Bayesian approach updates the probability of the estimations as more information becomes available. This allows us to reduce the required time for reliable earthquake signal detection from at least 3 seconds to 0.5 second. Furthermore, the initial error of hypocenter location estimation is reduced by 58%. The performance of the algorithm is further improved during aftershock sequences and swarm earthquakes.
\r\n\r\nSecondly, we introduce the use of multidimensional (KD tree) data structure to organize seismic database, so that the querying time can be reduced for the nearest neighbor search during earthquake source parameter estimation. The processing time of KD tree is approximately 15% of the processing time of linear exhaustive search, which allows the potential use of large seismic databases in real-time.
\r\n\r\nEEW is an interdisciplinary subject that involves collaboration among different scientific and engineering communities. Only by optimizing the warning time, such a unified system could be successful in taking protective actions before, during, and after earthquake natural disasters.
", "doi": "10.7907/Z9TH8JW4", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10352", "collection": "thesis", "collection_id": "10352", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07262017-074416397", "primary_object_url": { "basename": "Final_v2.pdf", "content": "final", "filesize": 24079945, "license": "other", "mime_type": "application/pdf", "url": "/10352/1/Final_v2.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Achieving Higher Fidelity Building Response through Emerging Technologies and Analytical Techniques", "author": [ { "family_name": "Massari", "given_name": "Anthony Thomas", "orcid": "0000-0002-6561-4674", "clpid": "Massari-Anthony-Thomas" } ], "thesis_advisor": [ { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197" } ], "thesis_committee": [ { "family_name": "Hall", "given_name": "John F.", "orcid": "0000-0002-7863-5060", "clpid": "Hall-J-F" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Kohler", "given_name": "Monica D.", "orcid": "0000-0002-4703-190X", "clpid": "Kohler-M-D" }, { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The integration of sensor technology into the built environment has created an opportunity for a new approach to infrastructure development and management. Using collected data and principles of general physics, we discuss means and methods of using low cost dense instrumentation to perform damage detection, structural identification, and the benefits of cyber physical systems to community resilience. A nonlinear damping strategy for braced frame structures is introduced incorporating capped levels of damping forces. The study shows the effect of having control of damping forces in nonlinear analysis and the importance of limiting energy dissipation to rational levels. The issue of sliding mass is also studied to determine the contribution to energy loss and the effect to overall response. The results indicate a need to incorporate this effect in stiff structures with intentionally decoupled mass such as data centers. Finally, a discussion on dual system structures under plastic deformation in a post event deformed configuration is presented. A suggested displacement based method for design is suggested for implementation into future editions of the building code.", "doi": "10.7907/Z9HH6H7N", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10879", "collection": "thesis", "collection_id": "10879", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05142018-133453405", "primary_object_url": { "basename": "Thesis_Marteau.pdf", "content": "final", "filesize": 11662230, "license": "other", "mime_type": "application/pdf", "url": "/10879/1/Thesis_Marteau.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Laboratory Studies of Granular Materials Under Shear: From Avalanches to Force Chains", "author": [ { "family_name": "Marteau", "given_name": "Elo\u00efse Sophie H\u00e9l\u00e8ne", "orcid": "0000-0001-7696-6264", "clpid": "Marteau-Elo\u00efse-Sophie-H\u00e9l\u00e8ne" } ], "thesis_advisor": [ { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Bhattacharya", "given_name": "Kaushik", "orcid": "0000-0003-2908-5469", "clpid": "Bhattacharya-K" }, { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Granular materials reveal their complexity and some of their unique features when subjected to shear deformation. They can dilate, behave like a solid or a fluid, and are known to carry external forces preferentially as force chains. In this dissertation, we employ laboratory experiments to study the complex behavior of granular materials under shear. We introduce a multiscale approach in which the underlying grain-scale mechanics are experimentally measured and homogenized to obtain enriched macroscopic quantities. First, we investigate granular avalanches spontaneously generated by a rotating drum. Measurements of grain kinematics are directly incorporated into a rate-dependent plasticity model that explains and reproduces the life cycle of laboratory avalanches. The results presented here feature dilatancy as the key material parameter governing the triggering of an avalanche. Second, we report a set of experiments performed on a custom-built mechanical device that allows a specimen composed of a two-dimensional analogue granular assembly to be subjected to quasi-static shear conditions. A numerical force inference technique, the Granular Element Method (GEM), provides direct observation and quantitative characterization of force chain structures in assemblies made of realistic grains. Equipped with a complete description of the grain-scale mechanics, we show that shear deformation creates geometrical (fabric) and mechanical (force) anisotropy. Finally, the influence of grain shape on grain-scale processes is studied. We find that grain interlocking is a prominent deformation mechanism for non-circular grains that ultimately promotes a significant increase in macroscopic shear strength. By seamlessly connecting grain-scale information to continuum scale experiments, this dissertation sheds light on the multiscale mechanical behavior of granular assemblies under shear.
", "doi": "10.7907/FKM0-P754", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10994", "collection": "thesis", "collection_id": "10994", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012018-015306089", "type": "thesis", "title": "Improving Seismic Collapse Risk Assessments of Steel Moment Frame Buildings", "author": [ { "family_name": "Buyco", "given_name": "John Kenneth", "orcid": "0000-0002-8182-7119", "clpid": "Buyco-John-Kenneth" } ], "thesis_advisor": [ { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" } ], "thesis_committee": [ { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Hall", "given_name": "John F.", "orcid": "0000-0002-7863-5060", "clpid": "Hall-J-F" }, { "family_name": "Kohler", "given_name": "Monica D.", "orcid": "0000-0002-4703-190X", "clpid": "Kohler-M-D" }, { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "It is important to be able to accurately assess seismic risk so that vulnerabilities can be prioritized for retrofit, emergency response procedures can be properly informed, and insurance rates can be sustainably priced to manage risk. To assess the risk of a building (or class of buildings) collapsing in a seismic event, procedures exist for creating one or more mathematical models of the structure of interest and performing nonlinear time history analysis with a large suite of input ground motions to calculate the building's seismic fragility and collapse risk. In this dissertation, three aspects of these procedures for assessing seismic collapse risk are investigated for the purpose of improving their accuracy.
\r\n\r\nIt is common to use spectral acceleration with a damping ratio of 5% as a ground motion intensity measure (IM) for assessing collapse fragility. In this dissertation, the use of 70%-damped spectral acceleration as an IM is investigated, with a focus on evaluating its sufficiency and efficiency. Incremental dynamic analysis (IDA) is performed for 22 steel moment frame (SMF) models with 50 biaxial ground motion records to formally evaluate the performance of 70%-damped spectral acceleration as an IM for highly nonlinear response and collapse. It is found that 70%-damped spectral acceleration is much more efficient than 5%-damped spectral acceleration and much more sufficient with respect to epsilon for all considered levels of highly nonlinear response. Its efficiency and sufficiency compares also compares well with more advanced IMs such as average spectral acceleration.
\r\n\r\nWhen selecting input ground motions for nonlinear time history analysis, most engineers select ground motion records from the NGA-West2 database, which are processed with high-pass filters to remove long-period noise. In this dissertation, the extent to which these filters remove actual ground motion that is relevant to nonlinear time history analysis is evaluated. 52 near-source ground motion records from large-magnitude events are considered. Some records are processed by applying high-pass filters and others are processed by record-specific tilt corrections. Raw and NGA-West2 records are also considered. IDA is performed for 9-, 20-, and 55-story steel moment frame models with these processed records to assess the effects of ground motion processing on the calculated collapse capacity. It is found that if the cutoff period (Tc) is at least 40 seconds, then applying a high-pass filter does not have more than a negligible effect on collapse capacity for any of the considered records or building models. For shorter Tc (e.g. 10 or 15 seconds), it is found that the filters sometimes have a large effect on calculated collapse capacity, in some cases by over 50%, even if Tc is much larger than the building\u2019s fundamental period. Of the considered ground motions, simply using the raw, uncorrected records usually yields more accurate results than using ground motions that have been processed with Tc less than or equal to 20 seconds.
\r\n\r\nFor an existing building with unknown design plans, one might perform a collapse risk assessment using an archetype model for which the specific member sizes are assumed based on the relevant design code and building site. In this dissertation, the sensitivity of seismic collapse risk estimates to design criteria and procedures are evaluated for six 9-story and four 20-story post-Northridge SMFs. These SMFs are designed for downtown Los Angeles using different design procedures according to ASCE 7-05 and ASCE 7-10. Seismic risk analysis is performed using the results of IDA with 44 ground motion records and the results are compared to those of pre-Northridge models. It is found that the collapse risk of 9-story SMFs designed according to performance-based design vary by 3x, owing to differences in GMPEs used to generate site-specific response spectra. There is generally less variation in the collapse risk estimates of 20-story post-Northridge SMFs when compared to 9-story post-Northridge SMFs because wind drift limits control the design of many members of the 20-story SMFs. Differences in collapse risk between pre- and post-Northridge SMFs are found to be at least 4x and 8x for the 9- and 20-story models, respectively. Furthermore, in response to four strong ground motion records from large-magnitude events, some of the 9-story and all of the 20-story pre-Northridge SMFs experience collapse and most of the post-Northridge SMFs experience significant damage (MIDR > 0.03).
", "doi": "10.7907/2SFH-WP06", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:11042", "collection": "thesis", "collection_id": "11042", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06072018-230955387", "type": "thesis", "title": "The Avatar Paradigm in Granular Materials", "author": [ { "family_name": "Kawamoto", "given_name": "Reid Yoshio", "orcid": "0000-0002-4936-5321", "clpid": "Kawamoto-Reid-Yoshio" } ], "thesis_advisor": [ { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" } ], "thesis_committee": [ { "family_name": "Bhattacharya", "given_name": "Kaushik", "orcid": "0000-0003-2908-5469", "clpid": "Bhattacharya-K" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Granular materials are ubiquitous in both everyday life and various engineering and industrial applications, ranging from breakfast cereal to sand to rice to medical pills. However, despite the familiarity of granular materials, their behavior is complex and efforts to characterize them are currently broad research areas in physics and engineering. Research of granular materials, as is the case with the research of other engineering materials such as rocks and metals, is beset with two gaps: the gap between reconciling macroscopic behavior with microscale (particle-scale, in the case of granular materials) behavior, and the gap between reconciling experimental and computational results. In this dissertation, we bridge these gaps through the \"avatar paradigm.\" The avatar paradigm is a two-step process that numerically characterizes (from experimental images) and simulates the shapes and behavior of individual particles, which we call avatars. First, we validate that our avatars are indeed capable of faithfully capturing particle kinematics and interparticle contact, then apply the characterization process, level set imaging (LS-imaging), to two experimental specimens to compute particle kinematics and contact statistics. We then detail a computational method, the level set discrete element method (LS-DEM), that is able to simulate the behavior of avatars, and apply it (and LS-imaging) to two other experimental specimens, calibrating the model to one specimen and using the results to predict the behavior of the other, thus providing some reconciliation between experimental and computational results. Finally, we use the avatar process to characterize and simulate yet another experimental specimen, this time analyzing the results at length scales ranging from particle behavior to local behavior to macroscopic behavior, further validating the ability of the avatar paradigm to bridge experiments and computations and showing its power to reconcile different length scales.", "doi": "10.7907/4fr8-bn91", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:9701", "collection": "thesis", "collection_id": "9701", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05042016-174005898", "primary_object_url": { "basename": "Thesis - Alex X. Jerves.pdf", "content": "final", "filesize": 27642710, "license": "other", "mime_type": "application/pdf", "url": "/9701/1/Thesis - Alex X. Jerves.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Microscopic Origin of Macroscopic Strength in Granular Media: A Numerical and Analytical Approach", "author": [ { "family_name": "Jerves Cobo", "given_name": "Alex Xavier", "orcid": "0000-0002-6556-8727", "clpid": "Jerves-Cobo-Alex-Xavier" } ], "thesis_advisor": [ { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" } ], "thesis_committee": [ { "family_name": "Ortiz", "given_name": "Michael", "orcid": "0000-0001-5877-4824", "clpid": "Ortiz-M" }, { "family_name": "Bruno", "given_name": "Oscar P.", "clpid": "Bruno-O-P" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Constitutive modeling in granular materials has historically been based on macroscopic experimental observations that, while being usually effective at predicting the bulk behavior of these type of materials, suffer important limitations when it comes to understanding the physics behind grain-to-grain interactions that induce the material to macroscopically behave in a given way when subjected to certain boundary conditions.
\r\n\t\r\nThe advent of the discrete element method (DEM) in the late 1970s helped scientists and engineers to gain a deeper insight into some of the most fundamental mechanisms furnishing the grain scale. However, one of the most critical limitations of classical DEM schemes has been their inability to account for complex grain morphologies. Instead, simplified geometries such as discs, spheres, and polyhedra have typically been used. Fortunately, in the last fifteen years, there has been an increasing development of new computational as well as experimental techniques, such as non-uniform rational basis splines (NURBS) and 3D X-ray Computed Tomography (3DXRCT), which are contributing to create new tools that enable the inclusion of complex grain morphologies into DEM schemes.
\r\n\t\r\nYet, as the scientific community is still developing these new tools, there is still a gap in thoroughly understanding the physical relations connecting grain and continuum scales as well as in the development of discrete techniques that can predict the emergent behavior of granular materials without resorting to phenomenology, but rather can directly unravel the micro-mechanical origin of macroscopic behavior.
\r\n\t\r\nIn order to contribute towards closing the aforementioned gap, we have developed a micro-mechanical analysis of macroscopic peak strength, critical state, and residual strength in two-dimensional non-cohesive granular media, where typical continuum constitutive quantities such as frictional strength and dilation angle are explicitly related to their corresponding grain-scale counterparts (e.g., inter-particle contact forces, fabric, particle displacements, and velocities), providing an across-the-scale basis for better understanding and modeling granular media.
\r\n\t\r\nIn the same way, we utilize a new DEM scheme (LS-DEM) that takes advantage of a mathematical technique called level set (LS) to enable the inclusion of real grain shapes into a classical discrete element method. After calibrating LS-DEM with respect to real experimental results, we exploit part of its potential to study the dependency of critical state (CS) parameters such as the critical state line (CSL) slope, CSL intercept, and CS friction angle on the grain's morphology, i.e., sphericity, roundness, and regularity.
\r\n\t\r\nFinally, we introduce a first computational algorithm to ``clone'' the grain morphologies of a sample of real digital grains. This cloning algorithm allows us to generate an arbitrary number of cloned grains that satisfy the same morphological features (e.g., roundness and aspect ratio) displayed by their real parents and can be included into a DEM simulation of a given mechanical phenomenon. In turn, this will help with the development of discrete techniques that can directly predict the engineering scale behavior of granular media without resorting to phenomenology.
\r\n", "doi": "10.7907/Z9GB2211", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9198", "collection": "thesis", "collection_id": "9198", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10052015-133333291", "primary_object_url": { "basename": "Janover_Christoper_2016_Thesis.pdf", "content": "final", "filesize": 20080290, "license": "other", "mime_type": "application/pdf", "url": "/9198/1/Janover_Christoper_2016_Thesis.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "SteelConverter and Caltech VirtualShaker: Rapid Nonlinear Cloud-Based Structural Model Conversion and Analysis", "author": [ { "family_name": "Janover", "given_name": "Christopher George", "clpid": "Janover-Christopher-George" } ], "thesis_advisor": [ { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" } ], "thesis_committee": [ { "family_name": "Hall", "given_name": "John F.", "orcid": "0000-0002-7863-5060", "clpid": "Hall-J-F" }, { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Kohler", "given_name": "Monica D.", "orcid": "0000-0002-4703-190X", "clpid": "Kohler-M-D" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "STEEL, the Caltech created nonlinear large displacement analysis software, is currently used by a large number of researchers at Caltech. However, due to its complexity, lack of visualization tools (such as pre- and post-processing capabilities) rapid creation and analysis of models using this software was difficult. SteelConverter was created as a means to facilitate model creation through the use of the industry standard finite element solver ETABS. This software allows users to create models in ETABS and intelligently convert model information such as geometry, loading, releases, fixity, etc., into a format that STEEL understands. Models that would take several days to create and verify now take several hours or less. The productivity of the researcher as well as the level of confidence in the model being analyzed is greatly increased.
\r\n\t\r\nIt has always been a major goal of Caltech to spread the knowledge created here to other universities. However, due to the complexity of STEEL it was difficult for researchers or engineers from other universities to conduct analyses. While SteelConverter did help researchers at Caltech improve their research, sending SteelConverter and its documentation to other universities was less than ideal. Issues of version control, individual computer requirements, and the difficulty of releasing updates made a more centralized solution preferred. This is where the idea for Caltech VirtualShaker was born. Through the creation of a centralized website where users could log in, submit, analyze, and process models in the cloud, all of the major concerns associated with the utilization of SteelConverter were eliminated. Caltech VirtualShaker allows users to create profiles where defaults associated with their most commonly run models are saved, and allows them to submit multiple jobs to an online virtual server to be analyzed and post-processed. The creation of this website not only allowed for more rapid distribution of this tool, but also created a means for engineers and researchers with no access to powerful computer clusters to run computationally intensive analyses without the excessive cost of building and maintaining a computer cluster.
\r\n\t\r\nIn order to increase confidence in the use of STEEL as an analysis system, as well as verify the conversion tools, a series of comparisons were done between STEEL and ETABS. Six models of increasing complexity, ranging from a cantilever column to a twenty-story moment frame, were analyzed to determine the ability of STEEL to accurately calculate basic model properties such as elastic stiffness and damping through a free vibration analysis as well as more complex structural properties such as overall structural capacity through a pushover analysis. These analyses showed a very strong agreement between the two softwares on every aspect of each analysis. However, these analyses also showed the ability of the STEEL analysis algorithm to converge at significantly larger drifts than ETABS when using the more computationally expensive and structurally realistic fiber hinges. Following the ETABS analysis, it was decided to repeat the comparisons in a software more capable of conducting highly nonlinear analysis, called Perform. These analyses again showed a very strong agreement between the two softwares in every aspect of each analysis through instability. However, due to some limitations in Perform, free vibration analyses for the three story one bay chevron brace frame, two bay chevron brace frame, and twenty story moment frame could not be conducted. With the current trend towards ultimate capacity analysis, the ability to use fiber based models allows engineers to gain a better understanding of a building\u2019s behavior under these extreme load scenarios.
\r\n\t\r\nFollowing this, a final study was done on Hall\u2019s U20 structure [1] where the structure was analyzed in all three softwares and their results compared. The pushover curves from each software were compared and the differences caused by variations in software implementation explained. From this, conclusions can be drawn on the effectiveness of each analysis tool when attempting to analyze structures through the point of geometric instability. The analyses show that while ETABS was capable of accurately determining the elastic stiffness of the model, following the onset of inelastic behavior the analysis tool failed to converge. However, for the small number of time steps the ETABS analysis was converging, its results exactly matched those of STEEL, leading to the conclusion that ETABS is not an appropriate analysis package for analyzing a structure through the point of collapse when using fiber elements throughout the model. The analyses also showed that while Perform was capable of calculating the response of the structure accurately, restrictions in the material model resulted in a pushover curve that did not match that of STEEL exactly, particularly post collapse. However, such problems could be alleviated by choosing a more simplistic material model.
\r\n", "doi": "10.7907/Z9SF2T3V", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9712", "collection": "thesis", "collection_id": "9712", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05092016-151847908", "primary_object_url": { "basename": "Mital_Utkarsh_2016_Complete_Thesis.pdf", "content": "final", "filesize": 5924203, "license": "other", "mime_type": "application/pdf", "url": "/9712/1/Mital_Utkarsh_2016_Complete_Thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Understanding Micro- and Macro-Mechanics of Soil Liquefaction: A Necessary Step for Field-Scale Assessment", "author": [ { "family_name": "Mital", "given_name": "Utkarsh", "orcid": "0000-0001-9794-382X", "clpid": "Mital-Utkarsh" } ], "thesis_advisor": [ { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" } ], "thesis_committee": [ { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" } ], "local_group": [ { "literal": "3MT Competition (Caltech)" }, { "literal": "div_eng" } ], "abstract": "Liquefaction is a devastating instability associated with saturated, loose, and cohesionless soils. It poses a significant risk to distributed infrastructure systems that are vital for the security, economy, safety, health, and welfare of societies. In order to make our cities resilient to the effects of liquefaction, it is important to be able to identify areas that are most susceptible. Some of the prevalent methodologies employed to identify susceptible areas include conventional slope stability analysis and the use of so-called liquefaction charts. However, these methodologies have some limitations, which motivate our research objectives. In this dissertation, we investigate the mechanics of origin of liquefaction in a laboratory test using grain-scale simulations, which helps (i) understand why certain soils liquefy under certain conditions, and (ii) identify a necessary precursor for onset of flow liquefaction. Furthermore, we investigate the mechanics of liquefaction charts using a continuum plasticity model; this can help in modeling the surface hazards of liquefaction following an earthquake. Finally, we also investigate the microscopic definition of soil shear wave velocity, a soil property that is used as an index to quantify liquefaction resistance of soil. We show that anisotropy in fabric, or grain arrangement can be correlated with anisotropy in shear wave velocity. This has the potential to quantify the effects of sample disturbance when a soil specimen is extracted from the field. In conclusion, by developing a more fundamental understanding of soil liquefaction, this dissertation takes necessary steps for a more physical assessment of liquefaction susceptibility at the field-scale.", "doi": "10.7907/Z9PV6HB0", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9712", "collection": "thesis", "collection_id": "9712", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05092016-151847908", "primary_object_url": { "basename": "Mital_Utkarsh_2016_Complete_Thesis.pdf", "content": "final", "filesize": 5924203, "license": "other", "mime_type": "application/pdf", "url": "/9712/1/Mital_Utkarsh_2016_Complete_Thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Understanding Micro- and Macro-Mechanics of Soil Liquefaction: A Necessary Step for Field-Scale Assessment", "author": [ { "family_name": "Mital", "given_name": "Utkarsh", "orcid": "0000-0001-9794-382X", "clpid": "Mital-Utkarsh" } ], "thesis_advisor": [ { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" } ], "thesis_committee": [ { "family_name": "Lapusta", "given_name": "Nadia", "orcid": "0000-0001-6558-0323", "clpid": "Lapusta-N" }, { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" } ], "local_group": [ { "literal": "3MT Competition (Caltech)" }, { "literal": "div_eng" } ], "abstract": "Liquefaction is a devastating instability associated with saturated, loose, and cohesionless soils. It poses a significant risk to distributed infrastructure systems that are vital for the security, economy, safety, health, and welfare of societies. In order to make our cities resilient to the effects of liquefaction, it is important to be able to identify areas that are most susceptible. Some of the prevalent methodologies employed to identify susceptible areas include conventional slope stability analysis and the use of so-called liquefaction charts. However, these methodologies have some limitations, which motivate our research objectives. In this dissertation, we investigate the mechanics of origin of liquefaction in a laboratory test using grain-scale simulations, which helps (i) understand why certain soils liquefy under certain conditions, and (ii) identify a necessary precursor for onset of flow liquefaction. Furthermore, we investigate the mechanics of liquefaction charts using a continuum plasticity model; this can help in modeling the surface hazards of liquefaction following an earthquake. Finally, we also investigate the microscopic definition of soil shear wave velocity, a soil property that is used as an index to quantify liquefaction resistance of soil. We show that anisotropy in fabric, or grain arrangement can be correlated with anisotropy in shear wave velocity. This has the potential to quantify the effects of sample disturbance when a soil specimen is extracted from the field. In conclusion, by developing a more fundamental understanding of soil liquefaction, this dissertation takes necessary steps for a more physical assessment of liquefaction susceptibility at the field-scale.", "doi": "10.7907/Z9PV6HB0", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9584", "collection": "thesis", "collection_id": "9584", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02242016-172347324", "primary_object_url": { "basename": "gokcan_karakus_2016_thesis.pdf", "content": "final", "filesize": 12792025, "license": "other", "mime_type": "application/pdf", "url": "/9584/1/gokcan_karakus_2016_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Real-Time Bayesian Analysis of Ground Motion Envelopes for Earthquake Early Warning", "author": [ { "family_name": "Karakus", "given_name": "Gokcan", "clpid": "Karakus-Gokcan" } ], "thesis_advisor": [ { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" } ], "thesis_committee": [ { "family_name": "Beck", "given_name": "James L.", "clpid": "Beck-J-L" }, { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Current earthquake early warning systems usually make magnitude and location predictions and send out a warning to the users based on those predictions. We describe an algorithm that assesses the validity of the predictions in real-time. Our algorithm monitors the envelopes of horizontal and vertical acceleration, velocity, and displacement. We compare the observed envelopes with the ones predicted by Cua & Heaton's envelope ground motion prediction equations (Cua 2005). We define a \"test function\" as the logarithm of the ratio between observed and predicted envelopes at every second in real-time. Once the envelopes deviate beyond an acceptable threshold, we declare a misfit. Kurtosis and skewness of a time evolving test function are used to rapidly identify a misfit. Real-time kurtosis and skewness calculations are also inputs to both probabilistic (Logistic Regression and Bayesian Logistic Regression) and nonprobabilistic (Least Squares and Linear Discriminant Analysis) models that ultimately decide if there is an unacceptable level of misfit. This algorithm is designed to work at a wide range of amplitude scales. When tested with synthetic and actual seismic signals from past events, it works for both small and large events.", "doi": "10.7907/Z9PN93JS", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9584", "collection": "thesis", "collection_id": "9584", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02242016-172347324", "primary_object_url": { "basename": "gokcan_karakus_2016_thesis.pdf", "content": "final", "filesize": 12792025, "license": "other", "mime_type": "application/pdf", "url": "/9584/1/gokcan_karakus_2016_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Real-Time Bayesian Analysis of Ground Motion Envelopes for Earthquake Early Warning", "author": [ { "family_name": "Karakus", "given_name": "Gokcan", "clpid": "Karakus-Gokcan" } ], "thesis_advisor": [ { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" } ], "thesis_committee": [ { "family_name": "Beck", "given_name": "James L.", "clpid": "Beck-J-L" }, { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" }, { "family_name": "Ampuero", "given_name": "Jean-Paul", "orcid": "0000-0002-4827-7987", "clpid": "Ampuero-J-P" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Current earthquake early warning systems usually make magnitude and location predictions and send out a warning to the users based on those predictions. We describe an algorithm that assesses the validity of the predictions in real-time. Our algorithm monitors the envelopes of horizontal and vertical acceleration, velocity, and displacement. We compare the observed envelopes with the ones predicted by Cua & Heaton's envelope ground motion prediction equations (Cua 2005). We define a \"test function\" as the logarithm of the ratio between observed and predicted envelopes at every second in real-time. Once the envelopes deviate beyond an acceptable threshold, we declare a misfit. Kurtosis and skewness of a time evolving test function are used to rapidly identify a misfit. Real-time kurtosis and skewness calculations are also inputs to both probabilistic (Logistic Regression and Bayesian Logistic Regression) and nonprobabilistic (Least Squares and Linear Discriminant Analysis) models that ultimately decide if there is an unacceptable level of misfit. This algorithm is designed to work at a wide range of amplitude scales. When tested with synthetic and actual seismic signals from past events, it works for both small and large events.", "doi": "10.7907/Z9PN93JS", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9321", "collection": "thesis", "collection_id": "9321", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12142015-083607823", "primary_object_url": { "basename": "Dizon_Abel_2016_Thesis.pdf", "content": "final", "filesize": 8019257, "license": "other", "mime_type": "application/pdf", "url": "/9321/1/Dizon_Abel_2016_Thesis.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "A Hybrid-Parallel Framework for the Nonlinear Seismic Analysis of Very Tall Buildings", "author": [ { "family_name": "Dizon", "given_name": "Abel Bermie Roberto", "clpid": "Dizon-Abel-Bermie-Roberto" } ], "thesis_advisor": [ { "family_name": "Hall", "given_name": "John F.", "orcid": "0000-0002-7863-5060", "clpid": "Hall-J-F" } ], "thesis_committee": [ { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" }, { "family_name": "Hall", "given_name": "John F.", "orcid": "0000-0002-7863-5060", "clpid": "Hall-J-F" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "orcid": "0000-0002-9112-6615", "clpid": "Kochmann-D-M" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "FRAME3D, a program for the nonlinear seismic analysis of steel structures, has previously been used to study the collapse mechanisms of steel buildings up to 20 stories tall. The present thesis is inspired by the need to conduct similar analysis for much taller structures. It improves FRAME3D in two primary ways.
\r\n\r\nFirst, FRAME3D is revised to address specific nonlinear situations involving large displacement/rotation increments, the backup-subdivide algorithm, element failure, and extremely narrow joint hysteresis. The revisions result in superior convergence capabilities when modeling earthquake-induced collapse. The material model of a steel fiber is also modified to allow for post-rupture compressive strength.
\r\n\r\nSecond, a parallel FRAME3D (PFRAME3D) is developed. The serial code is optimized and then parallelized. A distributed-memory divide-and-conquer approach is used for both the global direct solver and element-state updates. The result is an implicit finite-element hybrid-parallel program that takes advantage of the narrow-band nature of very tall buildings and uses nearest-neighbor-only communication patterns.
\r\n\r\nUsing three structures of varied sized, PFRAME3D is shown to compute reproducible results that agree with that of the optimized 1-core version (displacement time-history response root-mean-squared errors are ~\u301610\u3017^(-5) m) with much less wall time (e.g., a dynamic time-history collapse simulation of a 60-story building is computed in 5.69 hrs with 128 cores\u2014a speedup of 14.7 vs. the optimized 1-core version). The maximum speedups attained are shown to increase with building height (as the total number of cores used also increases), and the parallel framework can be expected to be suitable for buildings taller than the ones presented here.
\r\n\r\nPFRAME3D is used to analyze a hypothetical 60-story steel moment-frame tube building (fundamental period of 6.16 sec) designed according to the 1994 Uniform Building Code. Dynamic pushover and time-history analyses are conducted. Multi-story shear-band collapse mechanisms are observed around mid-height of the building. The use of closely-spaced columns and deep beams is found to contribute to the building's \u201csomewhat brittle\u201d behavior (ductility ratio ~2.0). Overall building strength is observed to be sensitive to whether a model is fracture-capable.
", "doi": "10.7907/Z96Q1V58", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9701", "collection": "thesis", "collection_id": "9701", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05042016-174005898", "primary_object_url": { "basename": "Thesis - Alex X. Jerves.pdf", "content": "final", "filesize": 27642710, "license": "other", "mime_type": "application/pdf", "url": "/9701/1/Thesis - Alex X. Jerves.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Microscopic Origin of Macroscopic Strength in Granular Media: A Numerical and Analytical Approach", "author": [ { "family_name": "Jerves Cobo", "given_name": "Alex Xavier", "orcid": "0000-0002-6556-8727", "clpid": "Jerves-Cobo-Alex-Xavier" } ], "thesis_advisor": [ { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" } ], "thesis_committee": [ { "family_name": "Ortiz", "given_name": "Michael", "orcid": "0000-0001-5877-4824", "clpid": "Ortiz-M" }, { "family_name": "Bruno", "given_name": "Oscar P.", "clpid": "Bruno-O-P" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Constitutive modeling in granular materials has historically been based on macroscopic experimental observations that, while being usually effective at predicting the bulk behavior of these type of materials, suffer important limitations when it comes to understanding the physics behind grain-to-grain interactions that induce the material to macroscopically behave in a given way when subjected to certain boundary conditions.
\r\n\t\r\nThe advent of the discrete element method (DEM) in the late 1970s helped scientists and engineers to gain a deeper insight into some of the most fundamental mechanisms furnishing the grain scale. However, one of the most critical limitations of classical DEM schemes has been their inability to account for complex grain morphologies. Instead, simplified geometries such as discs, spheres, and polyhedra have typically been used. Fortunately, in the last fifteen years, there has been an increasing development of new computational as well as experimental techniques, such as non-uniform rational basis splines (NURBS) and 3D X-ray Computed Tomography (3DXRCT), which are contributing to create new tools that enable the inclusion of complex grain morphologies into DEM schemes.
\r\n\t\r\nYet, as the scientific community is still developing these new tools, there is still a gap in thoroughly understanding the physical relations connecting grain and continuum scales as well as in the development of discrete techniques that can predict the emergent behavior of granular materials without resorting to phenomenology, but rather can directly unravel the micro-mechanical origin of macroscopic behavior.
\r\n\t\r\nIn order to contribute towards closing the aforementioned gap, we have developed a micro-mechanical analysis of macroscopic peak strength, critical state, and residual strength in two-dimensional non-cohesive granular media, where typical continuum constitutive quantities such as frictional strength and dilation angle are explicitly related to their corresponding grain-scale counterparts (e.g., inter-particle contact forces, fabric, particle displacements, and velocities), providing an across-the-scale basis for better understanding and modeling granular media.
\r\n\t\r\nIn the same way, we utilize a new DEM scheme (LS-DEM) that takes advantage of a mathematical technique called level set (LS) to enable the inclusion of real grain shapes into a classical discrete element method. After calibrating LS-DEM with respect to real experimental results, we exploit part of its potential to study the dependency of critical state (CS) parameters such as the critical state line (CSL) slope, CSL intercept, and CS friction angle on the grain's morphology, i.e., sphericity, roundness, and regularity.
\r\n\t\r\nFinally, we introduce a first computational algorithm to ``clone'' the grain morphologies of a sample of real digital grains. This cloning algorithm allows us to generate an arbitrary number of cloned grains that satisfy the same morphological features (e.g., roundness and aspect ratio) displayed by their real parents and can be included into a DEM simulation of a given mechanical phenomenon. In turn, this will help with the development of discrete techniques that can directly predict the engineering scale behavior of granular media without resorting to phenomenology.
\r\n", "doi": "10.7907/Z9GB2211", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:8885", "collection": "thesis", "collection_id": "8885", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05252015-121408938", "primary_object_url": { "basename": "Swetha_Veeraraghavan_2015_thesis.pdf", "content": "final", "filesize": 8247427, "license": "other", "mime_type": "application/pdf", "url": "/8885/1/Swetha_Veeraraghavan_2015_thesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Toppling Analysis of Precariously Balanced Rocks under Earthquake Excitation", "author": [ { "family_name": "Veeraraghavan", "given_name": "Swetha", "clpid": "Veeraraghavan-Swetha" } ], "thesis_advisor": [ { "family_name": "Krishnan", "given_name": "Swaminathan", "orcid": "0000-0002-2594-1523", "clpid": "Krishnan-S" }, { "family_name": "Hall", "given_name": "John F.", "orcid": "0000-0002-7863-5060", "clpid": "Hall-J-F" } ], "thesis_committee": [ { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Hudnut", "given_name": "Kenneth W.", "orcid": "0000-0002-3168-4797", "clpid": "Hudnut-K-W" }, { "family_name": "Krishnan", "given_name": "Swaminathan", "orcid": "0000-0002-2594-1523", "clpid": "Krishnan-S" }, { "family_name": "Hall", "given_name": "John F.", "orcid": "0000-0002-7863-5060", "clpid": "Hall-J-F" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Toppling analysis of a precariously balanced rock (PBR) can provide insights into the nature of ground motion that has not occurred at that location in the past and, by extension, realistic constraints on peak ground motions for use in engineering design. Earlier approaches have targeted simplistic 2-D models of the rock or modeled the rock-pedestal contact using spring-damper assemblies that require re-calibration for each rock. These analyses also assume that the rock does not slide on the pedestal. Here, a method to model PBRs in three dimensions is presented. The 3-D model is created from a point cloud of the rock, the pedestal, and their interface, obtained using Terrestrial Laser Scanning (TLS). The dynamic response of the model under earthquake excitation is simulated using a rigid body dynamics algorithm. The veracity of this approach is demonstrated by comparisons against data from shake table experiments. Fragility maps for toppling probability of the Echo Cliff PBR and the Pacifico PBR as a function of various ground motion parameters, rock-pedestal interface friction coefficient, and excitation direction are presented. The seismic hazard at these PBR locations is estimated using these maps. Additionally, these maps are used to assess whether the synthetic ground motions at these locations resulting from scenario earthquakes on the San Andreas Fault are realistic (toppling would indicate that the ground motions are unrealistically high).", "doi": "10.7907/Z98W3B9Z", "publication_date": "2015", "thesis_type": "phd", "thesis_year": "2015" } ]