Recursos de colección
Caltech Authors (141.170 recursos)
Repository of works by Caltech published authors.
Group = Earthquake Engineering Research Laboratory
Repository of works by Caltech published authors.
Group = Earthquake Engineering Research Laboratory
Taghavi Larigani, Shervin; Heaton, Thomas H.
[No abstract]
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...
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...
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...
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...
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...
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...
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...
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...
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...
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,...
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...
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...
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...
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...
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...
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...
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...
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...
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...