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rss_1.0 Recursos de colección

Caltech Authors (89,577 recursos)
Repository of works by Caltech published authors.

Group = Earthquake Engineering Research Laboratory

Mostrando recursos 1 - 20 de 284

1. 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...

2. 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...

3. 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...

4. 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...

5. 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...

6. 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...

7. 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,...

8. 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...

9. 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...

10. 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...

11. 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...

12. 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...

13. 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...

14. 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...

15. 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...

16. 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...

17. Analysis of Simultaneous Operational Failure of Critical Facilities due to Earthquake, for a California Utlity - Porter, Keith A.; Krishnan, Swaminathan; Xu, Xin
This study presents an estimate of the probability that a single earthquake could cause simultaneous operational failure of geographically disperse data centers operated by a California utility. Three facilities are considered: a grid control facility (denoted herein by GCF), a data processing facility (DPF), and a backup data facility (BDF) that can perform the functions of either GCF or DPF, should either be rendered inoperative. This study estimates two probabilities: (1) that within the next 5 years a single earthquake could render both the grid control and backup facilities inoperative; and (2) that within the next 5 years a single earthquake could render both the data processing...

18. Seismic Early Warning Systems: Procedure for Automated Decision Making - Grasso, Veronica F.; Beck, James L.; Manfredi, Gaetano
An Early Warning System potentially allows mitigation measures to be carried out from the moment in which a seismic event is detected. Examples of such measures are evacuation of buildings, shut-down of critical systems (nuclear reactors, industrial chemical processes, etc.) and stopping of high-speed trains. The type of mitigation measures that can be effectively activated depends on the amount of warning time available, but timeliness is often in conflict with the reliability of the predictions, which become more accurate as more seismic sensor data is collected. There is therefore an inevitable trade-off between the amount of warning time available and...

19. Performance of 18-Story Steel Momentframe Buildings during a large San Andreas Earthquake - A Southern California-Wide End-to-End Simulation - Krishnan, Swaminathan; Ji, Chen; Komatitsch, Dimitri; Tromp, Jeroen
The mitigation of seismic risk in urban areas in the United States and abroad is of major concern for all governments. Unfortunately no comprehensive studies have attempted to address this issue in a rigorous, quantitative manner. This study tackles this problem head-on for one typical class of tall buildings in southern California. The approach adopted here can be used as a template to study earthquake risk in other seismically sensitive regions of the world, such as Taiwan, Japan, Indonesia, China, South American countries (Chile, Bolivia, etc.), and the west coast of the United States (in particular, Seattle). In 1857 a large earthquake of magnitude 7.9 [1]...

20. Creating the Virtual Seismologist: developments in ground motion characterization and seismic early warning - Cua, Georgia B.
Abstract The Virtual Seismologist method for earthquake early warning uses a Bayesian approach to find the most probable magnitude and location estimates given the incoming ground motions envelopes from a rupturing earthquake. Ground motion ratios and ground motion envelope attenuation relationships are used to estimate magnitude and epicentral location as early as 3 seconds after the initial P wave detection. The use of prior information distinguishes this method from other proposed methods for seismic early warning. The state of health of the seismic network, previously observed seismicity, fault locations, and the Gutenberg-Richter relationship are the types of prior information useful in resolving trade-offs in the initial source estimates which are...

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