Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (20 results)

  • Article
SEMM Reports Series (2012)
    Cover page: Three-dimensional nonlinear cyclic beam-truss model for non-planar reinforced concrete walls
    • Article
    SEMM Reports Series (2013)
      Cover page: Characterization and representation of pulse-like ground motions using cumulative pulse extraction via wavelet analysis
      • Article
      SEMM Reports Series (2013)
        Cover page: Nonlinear seismic site response and soil foundation structure interaction of a 20-story structural wall building subjected to pulse-like excitation
        • Thesis
        • Peer Reviewed
        UC Berkeley Electronic Theses and Dissertations (2014)

        This dissertation approaches the subject of three-dimensional (3D) seismic analysis of reinforced concrete (RC) wall buildings at near-fault sites by first studying two main problems separately: (1) the characterization of base excitation for buildings located at near-fault sites, and (2) modeling the behavior of RC buildings accurately including inelastic behavior and the failure mode. The dissertation culminates with the 3D response history analysis of two 20-story RC core wall buildings models, including the slabs and columns, subject to a strong near-fault ground motion record.

        First, the presence and characteristics of multiple pulses [with dominant period TP between 0.5 and 12 s] in historical near-fault ground motion records is studied. An iterative method for extracting multiple strong pulses imbedded in a ground motion is presented. The method is used to extract multiple strong velocity pulses from the fault-normal horizontal component of 40 pulse-like ground motion records from 17 historical earthquakes, with magnitudes ranging from MW6.3 to MW7.9, recorded at a distance less than 10 km from the fault rupture with a peak ground velocity greater than 0.6 m / s. The relationships between the dominant period of the extracted pulses, associated amplitudes, and earthquake magnitude are presented, indicating that the amplitude of the strongest pulses with 1.5 s ≤ TP ≤ 5 s, does not depend significantly on the earthquake magnitude.

        Next, the effect of soil-foundation-structure interaction (SFSI) for a 20-story core wall building with a caisson foundation subject to single pulse motions is investigated using two-dimensional (2D) nonlinear finite-elements and fiber beam-column elements; nonlinear site effects on the free-field motion and structural response is discussed. The nonlinear site effects for free-field motions result in a de-amplification of peak surface acceleration due to soil yielding, and a maximum of 64% amplification of peak acceleration and velocity of at specific pulse periods for deep soils. SFSI, after removing the nonlinear site effect, has a negligible effect on the maximum value of peak roof acceleration and peak roof drift ratio over the pulse periods considered; however, the effect of the increased flexibility due to SFSI is observed in the peak drift ratio and peak base shear response.

        A couple of chapters of this dissertation are dedicated to the development and verification of a three-dimensional nonlinear cyclic modelling method for non-planar reinforced concrete walls and slabs. This modeling approached - called the beam-truss model (BTM) - consists of (i) nonlinear Euler-Bernoulli fiber-section beam elements representing the steel and concrete in the vertical and horizontal direction, and (ii) nonlinear trusses representing the concrete in the diagonal directions. The model represents the effects of flexure-shear interaction (FSI) by computing the stress and strains in the horizontal and vertical directions and by considering biaxial effects on the behavior of concrete diagonals. In addition, the BTM explicitly models diagonal compression and tension failures (shear failures) under cyclic or dynamic loading. The BTM is first validated by comparing the experimentally measured and numerically computed response of eight RC walls subjected to static cyclic loading, including two non-planar RC walls under biaxial cyclic loading. Then, the BTM is extended to modeling slabs and validated with a two-bay slab-column specimen. Finally, the BTM is validated by comparing the experimentally measured and numerically computed response and failure mode of a 5-story coupled wall RC building under seismic base excitation.

        The final chapter presents the 3D response history analysis of two 20-story RC core wall buildings subject to a strong near-fault ground motion record. The 20-story building model includes the RC core wall, post-tensioned slabs, and columns; the core wall and slabs are modeled using the developed BTM while the columns are modeled with fiber-section beam-column elements. The two 20-story RC core wall buildings considered have similar geometry: one is conventionally designed to develop plastic hinging at the base of the core-wall, and the second is designed with a damage resistant structural system that combines two seismic isolation planes. Analysis is conducted using the two horizontal components of the historical TCU52 ground motion recorded 0.7 km from the fault plane of the MW7.6 1999 Chi-chi, Taiwan earthquake. The seismic response and damage of the two buildings is discussed.

          Cover page: Three-dimensional Seismic Analysis of Reinforced Concrete Wall Buildings at Near-fault Sites
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2024)
            Cover page: Theory of topological defects and textures in two-dimensional quantum orders with spontaneous symmetry breaking
            • Article
            • Peer Reviewed
            UC Irvine Previously Published Works (2016)
            The anyonic excitations of a spin liquid can feature fractional quantum numbers under space group symmetries. Detecting these fractional quantum numbers, which are analogs of the fractional charge of Laughlin quasiparticles, may prove easier than the direct observation of anyonic braiding and statistics. Motivated by the recent numerical discovery of spin-liquid phases in the kagome Heisenberg antiferromagnet, we theoretically predict the pattern of space group symmetry fractionalization in the kagome lattice SO(3)-symmetric chiral spin liquid. We provide a method to detect these fractional quantum numbers in finite-size numerics which is simple to implement in the density matrix renormalization group. Applying these developments to the chiral spin liquid phase of a kagome Heisenberg model, we find perfect agreement between our theoretical prediction and numerical observations.
              Cover page: Space Group Symmetry Fractionalization in a Chiral Kagome Heisenberg Antiferromagnet
              • Article
              • Peer Reviewed
              UC Riverside Previously Published Works (1998)
                • Article
                • Peer Reviewed
                UC Berkeley Previously Published Works (2023)
                The propagation of spin waves in magnetically ordered systems has emerged as a potential means to shuttle quantum information over large distances. Conventionally, the arrival time of a spin wavepacket at a distance, d, is assumed to be determined by its group velocity, vg. Here, we report time-resolved optical measurements of wavepacket propagation in the Kagome ferromagnet Fe3Sn2 that demonstrate the arrival of spin information at times significantly less than d/vg. We show that this spin wave "precursor" originates from the interaction of light with the unusual spectrum of magnetostatic modes in Fe3Sn2. Related effects may have far-reaching consequences toward realizing long-range, ultrafast spin wave transport in both ferromagnetic and antiferromagnetic systems.
                  Cover page: Spin wavepackets in the Kagome ferromagnet Fe3Sn2: Propagation and precursors
                  • Article
                  • Peer Reviewed
                  UC Davis Previously Published Works (2015)
                  NMDA receptors (NMDARs) play an essential role in some forms of synaptic plasticity, learning, and memory. Therefore, these receptors are highly regulated with respect to their localization, activation, and abundance both within and on the surface of mammalian neurons. Fundamental questions remain, however, regarding how this complex regulation is achieved. Using cell-based models and F-box Only Protein 2 (Fbxo2) knock-out mice, we found that the ubiquitin ligase substrate adaptor protein Fbxo2, previously reported to facilitate the degradation of the NMDAR subunit GluN1 in vitro, also functions to regulate GluN1 and GluN2A subunit levels in the adult mouse brain. In contrast, GluN2B subunit levels are not affected by the loss of Fbxo2. The loss of Fbxo2 results in greater surface localization of GluN1 and GluN2A, together with increases in the synaptic markers PSD-95 and Vglut1. These synaptic changes do not manifest as neurophysiological differences or alterations in dendritic spine density in Fbxo2 knock-out mice, but result instead in increased axo-dendritic shaft synapses. Together, these findings suggest that Fbxo2 controls the abundance and localization of specific NMDAR subunits in the brain and may influence synapse formation and maintenance.
                    Cover page: Loss of F-box Only Protein 2 (Fbxo2) Disrupts Levels and Localization of Select NMDA Receptor Subunits, and Promotes Aberrant Synaptic Connectivity
                    • Article
                    • Peer Reviewed
                    UCLA Previously Published Works (2022)

                    Introduction

                    Therapeutic options for type 2 diabetes mellitus (T2DM) have expanded over the last decade with the emergence of cardioprotective novel agents, but without such data for older drugs, leaving a critical gap in our understanding of the relative effects of T2DM agents on cardiovascular risk.

                    Methods and analysis

                    The large-scale evidence generations across a network of databases for T2DM (LEGEND-T2DM) initiative is a series of systematic, large-scale, multinational, real-world comparative cardiovascular effectiveness and safety studies of all four major second-line anti-hyperglycaemic agents, including sodium-glucose co-transporter-2 inhibitor, glucagon-like peptide-1 receptor agonist, dipeptidyl peptidase-4 inhibitor and sulfonylureas. LEGEND-T2DM will leverage the Observational Health Data Sciences and Informatics (OHDSI) community that provides access to a global network of administrative claims and electronic health record data sources, representing 190 million patients in the USA and about 50 million internationally. LEGEND-T2DM will identify all adult, patients with T2DM who newly initiate a traditionally second-line T2DM agent. Using an active comparator, new-user cohort design, LEGEND-T2DM will execute all pairwise class-versus-class and drug-versus-drug comparisons in each data source, producing extensive study diagnostics that assess reliability and generalisability through cohort balance and equipoise to examine the relative risk of cardiovascular and safety outcomes. The primary cardiovascular outcomes include a composite of major adverse cardiovascular events and a series of safety outcomes. The study will pursue data-driven, large-scale propensity adjustment for measured confounding, a large set of negative control outcome experiments to address unmeasured and systematic bias.

                    Ethics and dissemination

                    The study ensures data safety through a federated analytic approach and follows research best practices, including prespecification and full disclosure of results. LEGEND-T2DM is dedicated to open science and transparency and will publicly share all analytic code from reproducible cohort definitions through turn-key software, enabling other research groups to leverage our methods, data and results to verify and extend our findings.
                      Cover page: Large-scale evidence generation and evaluation across a network of databases for type 2 diabetes mellitus (LEGEND-T2DM): a protocol for a series of multinational, real-world comparative cardiovascular effectiveness and safety studies
                      Top