Recursos de colección

Caltech Authors (141.170 recursos)

Repository of works by Caltech published authors.

Group = Earthquake Engineering Research Laboratory

Mostrando recursos 1 - 20 de 288

  1. Can you measure the weight of a truck with a commercial camera?

    Taghavi Larigani, Shervin; Heaton, Thomas H.
    [No abstract]

  2. Interpretation of Millikan Library's Vibrating Modes Using A Magneto Coil To Measure Phase Shifts

    Cheng, Ming Hei; Heaton, Thomas H.; Kohler, Monica D.
    A new set of natural frequencies for the 9-story reinforced concrete Millikan Library building on the Caltech campus is computed using the observed phase shift between the driving force of a shaker installed on the building’s roof and structural response at resonance. The phase of the shaker’s output force was recorded by a magneto coil and magnet attached to the shaker’s rotating mechanism, and the phase of the structural response was obtained from acceleration time series recorded by an accelerometer on the roof. These new results refute previous studies’ identification of the 3rd EW and 2nd torsional modes which used...

  3. Characterizing Deformation of Buildings from Videos

    Taghavi Larigani, Shervin; Heaton, Thomas H.
    We have started to explore the feasibility of extracting useful data on the deformation of buildings and structures based on optical videos, (Taghavi Larigani & Heaton). In the beginning, we look at the characterizations and limitations of the hardware, which is composed of a high-quality digital camera, combined with its optical imaging system capturing a video-footage of the structure under test, and then introduce a straightforward targets-tracking algorithm that produces the time-series displacements of targets that we select on the video. We performed preliminary measurements consisting of testing our targets-tracking algorithm using high definition format videos displaying the structures that...

  4. Characterizing Average Properties of Southern California Ground Motion Amplitudes and Envelopes

    Cua, Georgia; Heaton, Thomas H.
    We examine ground motion envelopes of horizontal and vertical acceleration, velocity, and filtered displacement recorded within 200 km from southern California earthquakes in the magnitude range 2 < M ≤ 7.3. We introduce a parameterization that decomposes the observed ground motion envelope into P-wavetrain, S-wavetrain, and ambient noise envelopes. The shape of the body wave envelopes as a function of time is further parameterized by a rise time, a duration, a constant amplitude, and 2 coda decay parameters. Each observed ground motion envelope can thus be described by 11 envelope parameters. We fit this parameterization to 30,000 observed ground motion...

  5. Stochastic Analysis, Model and Reliability Updating of Complex Systems with Applications to Structural Dynamics

    Cheung, Sai Hung
    In many engineering applications, it is a formidable task to construct mathematical models that are expected to produce accurate predictions of the behavior of a system of interest. During the construction of such predictive models, errors due to imperfect modeling and uncertainties due to incomplete information about the system and its environment (e.g., input or excitation) always exist and can be accounted for appropriately by using probability logic. To assess the system performance subjected to dynamic excitations, a stochastic system analysis considering all the uncertainties involved has to be performed. In engineering, evaluating the robust failure probability (or its complement, robust reliability) of the system is a very...

  6. Earthquake Ground Motion Simulation using Novel Machine Learning Tools

    Alimoradi, Arzhang
    A novel method of model-independent probabilistic seismic hazard analysis(PSHA) and ground motion simulation is presented and verified using previously recorded data and machine learning. The concept of “eigenquakes” is introduced as an orthonormal set of basis vectors that represent characteristic earthquake records in a large database. Our proposed procedure consists of three phases, (1) estimation of the anticipated level of shaking for a scenario earthquake at a site using Gaussian Process regression, (2) extraction of the eigenquakes from Principal Component Analysis (PCA) of data, and (3) optimal combination of the eigenquakes to generate time-series of ground acceleration with spectral ordinates...

  7. Mechanism of Collapse, Sensitivity to Ground Motion Features, and Rapid Estimation of the Response of Tall Steel Moment Frame Buildings to Earthquake Excitation

    Krishnan, Swaminathan; Muto, Matthew
    This study explores the behavior of two tall steel moment frame buildings and their variants under strong earthquake ground shaking through parametric analysis using idealized ground motion waveforms. Both fracture-susceptible as well as perfect-connection conditions are investigated. Ground motion velocity waveforms are parameterized using triangular (sawtooth-like) wave-trains with a characteristic period (T), amplitude(peak ground velocity, PGV ), and duration (number of cycles, N). This idealized representation has the desirable feature that the response of the target buildings under the idealized waveforms closely mimics their response under the emulated true ground motion waveforms. A suite of nonlinear analyses are performed on four tall building models subjected...

  8. Case study of the collapse of a water tank

    Krishnan, Swaminathan
    A 48.76m high water tank with the supporting steel lattice comprising 5 segments with uniform member configuration is conceived. Its collapse behavior is investigated through a suite of ground motion analyses. First, the tank is analyzed under 13 three-component ground motion records from the Chi-Chi and Hokkaido earthquakes. It is shown that the tank always collapses in the same manner as a result of overturning due to P-Delta instability resulting from column and brace buckling at the base. This is the consequence of the uniform member sizing in each of the five segments of the supporting lattice. Incremental dynamic analyses are...

  9. On the Modeling of Elastic and Inelastic, Critical- and Post-Buckling Behavior of Slender Columns and Bracing Members

    Krishnan, Swaminathan
    Analyzing tall braced frame buildings with thousands of degrees of freedom in three dimensions subject to strong earthquake ground motion requires an efficient brace element that can capture the overall features of its elastic and inelastic response under axial cyclic loading without unduly heavy discretization. This report details the theory of a modified elastofiber (MEF) element developed to model braces and buckling-sensitive slender columns in such structures. The MEF element consists of three fiber segments, two at the member ends and one at mid-span, with two elastic segments sandwiched in between. The segments are demarcated by two exterior nodes and four interior nodes. The fiber segments...

  10. FRAME3D V2.0 - A Program for the Three-Dimensional Nonlinear Time-History Analysis of Steel Structures: User Guide

    Krishnan, Swaminathan
    This is Version 2.0 of the user guide and should be used along with Version 2.0 of the program. Updates include: 1. Realistic PMM interaction surfaces for plastic hinge elements (output file PMM). 2. 5-Segment modified elastofiber element for brace and slender column modeling. 3. Eigen value problem solver using subspace iteration (output files MODES and EIGEN). 4. Output the sum of forces of groups of elements (output file ELMGRPRES). Additional input is required as a result of these additions to the program. However, the example input files shown in chapter 6 correspond to the input format from Version 1.0 and do not reflect the changes...

  11. New Bayesian Updating Methodology for Model Validation and Robust Predictions Based on Data from Hierarchical Subsystem Tests

    Cheung, Sai Hung; Beck, James
    In many engineering applications, it is a formidable task to construct a mathematical model that is expected to produce accurate predictions of the behavior of a system of interest. During the construction of such predictive models, errors due to imperfect modeling and uncertainties due to incomplete information about the system and its input always exist and can be accounted for appropriately by using probability logic. Often one has to decide which proposed candidate models are acceptable for prediction of the target system behavior. In recent years, the problem of developing an effective model validation methodology has attracted attention in many different fields of engineering and applied science. Here,...

  12. Steel Moment-Resisting Frame Responses in Simulated Strong Ground Motions: or How I Learned to Stop Worrying and Love the Big One

    Olsen, Anna
    This thesis studies the response of steel moment-resisting frame buildings in simulated strong ground motions. I collect 37 simulations of crustal earthquakes in California. These ground motions are applied to nonlinear finite element models of four types of steel moment frame buildings: six- or twenty-stories with either a stiffer, higherstrength design or a more flexible, lower-strength design. I also consider the presence of fracture-prone welds in each design. Since these buildings experience large deformations in strong ground motions, the building states considered in this thesis are collapse, total structural loss (must be demolished), and if repairable, the peak interstory drift. This thesis maps these building responses on the...

  13. A Plasticity Model to Predict the Effects of Confinement on Concrete

    Wolf, Julie Anne
    A plasticity model to predict the behavior of confined concrete is developed. The model is designed to implicitly account for the increase in strength and ductility due to confining a concrete member. The concrete model is implemented into a finite element (FE) model. By implicitly including the change in the strength and ductility in the material model, the confining material can be explicitly included in the FE model. Any confining material can be considered, and the effects on the concrete of failure in the confinement material can be modeled. Test data from a wide variety of different concretes utilizing different confinement methods are used to estimate the model...

  14. Bayesian Learning for Earthquake Engineering Applications and Structural Health Monitoring

    Oh, Chang Kook
    Parallel to significant advances in sensor hardware, there have been recent developments of sophisticated methods for quantitative assessment of measured data that explicitly deal with all of the involved uncertainties, including inevitable measurement errors. The existence of these uncertainties often causes numerical instabilities in inverse problems that make them ill-conditioned. The Bayesian methodology is known to provide an efficient way to alleviate this illconditioning by incorporating the prior term for regularization of the inverse problem, and to provide probabilistic results which are meaningful for decision making. In this work, the Bayesian methodology is applied to inverse problems in earthquake engineering and especially to structural health monitoring. The proposed methodology of...

  15. An Ounce of Prevention: Probabilistic Loss Estimation for Performance-Based Earthquake Engineering

    Mitrani-Reiser, Judith
    Performance-based earthquake engineering (PBEE) is a methodology that incorporates desired performance levels into the design process. Performance in PBEE can be expressed in economic terms, or as elapsed downtime, or in terms of life and building safety objectives. These performance objectives are relevant to various types of stakeholders. They should be addressed in building loss estimation procedures because after an earthquake, the repair cost will not be the only "loss" suffered by building stakeholders. In a sizeable earthquake, there will likely also be some losses due to business interruption during the repair effort, building closure taken as a post-earthquake safety precaution, and human casualties caused by building failures...

  16. Stochastic System Design and Applications to Stochastically Robust Structural Control

    Taflanidis, Alexandros
    The knowledge about a planned system in engineering design applications is never complete. Often, a probabilistic quantification of the uncertainty arising from this missing information is warranted in order to efficiently incorporate our partial knowledge about the system and its environment into their respective models. In this framework, the design objective is typically related to the expected value of a system performance measure, such as reliability or expected life-cycle cost. This system design process is called stochastic system design and the associated design optimization problem stochastic optimization. In this thesis general stochastic system design problems are discussed. Application of this design approach to the specific field of structural...

  17. Early Warning for Earthquakes with Large Rupture Dimension

    Yamada, Masumi
    Earthquake early warning systems have become popular these days, and many seismologists and engineers are making research efforts for their practical application. The existing earthquake early warning systems provide estimates of the location and size of earthquakes, and then ground motions at a site are estimated as a function of the epicentral distance and site soil properties. However, for large earthquakes, the energy is radiated from a large area surrounding the entire fault plane, and the epicenter indicates only where rupture starts. In this project, we focus on an earthquake early warning system considering fault finiteness. We provide a new methodology...

  18. Application of Stochastic Simulation Methods to System Identification

    Muto, Matthew
    Reliable predictive models for the response of structures are a necessity for many branches of earthquake engineering, such as design, structural control, and structural health monitoring. However, the process of choosing an appropriate class of models to describe a system, known as model-class selection, and identifying the specific predictive model based on available data, known as system identification, is difficult. Variability in material properties, complex constitutive behavior, uncertainty in the excitations caused by earthquakes, and limited constraining information (relatively few channels of data, compared to the number of parameters needed for a useful predictive model) make system identification an ill-conditioned problem. In addition, model-class selection is not trivial, as...

  19. Time-Frequency Analysis of Systems with Changing Dynamic Properties

    Bradford, Samuel Case
    Time-frequency analysis methods transform a time series into a two-dimensional representation of frequency content with respect to time. The Fourier Transform identifies the frequency content of a signal (as a sum of weighted sinusoidal functions) but does not give useful information regarding changes in the character of the signal, as all temporal information is encoded in the phase of the transform. A time-frequency representation, by expressing frequency content at different sections of a record, allows for analysis of evolving signals. The time-frequency transformation most commonly encountered in seismology and civil engineering is a windowed Fourier Transform, or spectrogram; by comparing the frequency content of the first portion of...

  20. Uncertainty Propagation and Feature Selection for Loss Estimation in Performance-based Earthquake Engineering

    Ching, Jianye; Porter, Keith A.; Beck, James L.
    This report presents a new methodology, called moment matching, of propagating the uncertainties in estimating repair costs of a building due to future earthquake excitation, which is required, for example, when assessing a design in performance-based earthquake engineering. Besides excitation uncertainties, other uncertain model variables are considered, including uncertainties in the structural model parameters and in the capacity and repair costs of structural and non-structural components. Using the first few moments of these uncertain variables, moment matching requires only a few well-chosen point estimates to propagate the uncertainties to estimate the first few moments of the repair costs with high...

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