65 research outputs found
High-fidelity inelastic post-buckling response for balanced design and performance improvement of X-braced moment resisting frames
In this paper, the nonlinear post buckling response of X-Braced Moment Resisting Frame (X-BMRF) systems are studied. The X-BMRF comprises of X-bracing diagonals attached to the moment frame by corner gusset plates to form the structural system acting as a dual frame. In common practice today, one of the X-bracing diagonal members is discontinuous, and a middle gusset plate is used to connect the diagonals to each other at the intersection. In this study, the effect of mid-connection details and different types sizes of corner gusset plate connection are well measured to evaluate behavioral characteristics of the above systems. An accurate and robust three-dimensional finite element modeling of the above systems validatedverified against available test data and numerical simulation are demonstrated. Then, a number of X-BMRFs are designed and analyzed under monotonic (and cyclic) loading(s), and later ductility values and energy dissipation ratios of such systems are appraised. The results are used to evaluate the secondary yield mechanisms, probable failure modes, and to quantify the loading share of story shear when different rigidity ratios between the X-bracing and moment frame systems are deliberated. Finally, the results can provide a suitable ground to present a new set of balanced design criteria which can improve nonlinear performance and assure maximum system ductility of such system
Automatic Roof Type Classification Through Machine Learning for Regional Wind Risk Assessment
Roof type is one of the most critical building characteristics for wind
vulnerability modeling. It is also the most frequently missing building feature
from publicly available databases. An automatic roof classification framework
is developed herein to generate high-resolution roof-type data using machine
learning. A Convolutional Neural Network (CNN) was trained to classify roof
types using building-level satellite images. The model achieved an F1 score of
0.96 on predicting roof types for 1,000 test buildings. The CNN model was then
used to predict roof types for 161,772 single-family houses in New Hanover
County, NC, and Miami-Dade County, FL. The distribution of roof type in city
and census tract scales was presented. A high variance was observed in the
dominant roof type among census tracts. To improve the completeness of the
roof-type data, imputation algorithms were developed to populate missing roof
data due to low-quality images, using critical building attributes and
neighborhood-level roof characteristics
Nonlinear Time-History Analysis of Soil-Structure Systems Incorporating Frequency-Dependent Impedance Functions
To accurately analyze structures, soil-structure interaction effects must be
taken into account. One approach is to create a complete finite element model
of the full system wherein the soil is represented as a semi-infinite domain.
This direct method is frequently adopted in research studies, but it is
typically avoided in engineering practice due to the labor-intensive model
development, and the high computational cost. In practice, soil-structure
interaction analysis is mostly carried out through a substructure approach
where the superstructure is modeled through a detailed model and is placed on a
soil-foundation substructure which is represented by a system called impedance
function. Then, the entire system is analyzed under foundation input motions.
While the method is theoretically designed for linear-elastic behavior, it can
be partially applied to nonlinear systems too. Although impedance functions for
various soil and foundation configurations can be obtained from analytical,
numerical, or experimental analyses, their implementation in the time-domain is
not trivial because they are frequency-dependent. A simple solution for this
problem has been to convert them to some physical models with
frequency-independent components, but there is no straightforward way to
connect these components. More importantly, the coefficients of these
components could be non-physical parameters that cannot be modeled in software
like OpenSEES. To resolve these problems, various alternative approaches have
been proposed in the literature. In this project, we review some of the
existing solutions and verify them through numerical examples. After extensive
review and evaluation, the Hybrid Time Frequency Domain method seems a more
practical solution with fewer stability issues. This method is implemented in
Opensees to be used by researchers and practitioners
Effects of Near-Fault Ground Motions on Civil Infrastructure
Near-fault earthquakes (NFEs), characterized by high peak ground velocity (PGV) and long
period pulses, show different properties from far-field ones. The input motions from NFEs are
usually composed of a small number of sinusoidal large waves in addition to significant
vertical components. These specific characteristics of NFEs strongly influence the seismic
response of civil infrastructure and may reduce the effectiveness of the adopted protection
devices
A Data-Driven Approach for Granular Simulation of Potential Earthquake Damage to Bridge Networks and Resulting Decreases in Mobility
Quantified investigation of resilience in regional transportation networks has been a growing research focus. Despite this increased attention, state-of-the-art studies fall short of devising and utilizing explicit transportation network models where infrastructure components (roads, bridges, etc.) and travel behaviors of network users are modeled in high fidelity. This study presents a novel model-based approach that couples a semi-automated, image-based structure-specific bridge modeling method with a metropolis-scale travel demand model towards achieving a comprehensive and high-resolution resilience assessment. As a result of its data-driven approach, the proposed method is capable of capturing and incorporating many details that are usually omitted in traditional analyses, promising improved accuracy in estimating the resilience and sustainability metrics of transportation networks. As a small-scale testbed for the proposed approach, this study displays the results of a preliminary investigation of potential seismic losses for the Los Angeles Metropolitan Area due to a hazard-consistent scenario earthquake primarily affecting the Ports of Los Angeles and Long Beach. This analysis makes use of structure-specific fragility functions of 200 bridges in the vicinity of the port facilities, generated from street-level imagery, and provides a detailed picture of the expected disruptions to truck freight mobility resulting from the scenario event
Centrifuge Testing of Circular and Rectangular Embedded Structures with Base Excitations
We present data and metadata from a centrifuge testing program that was designed to investigate the seismic responses of buried circular and rectangular culverts. The specimen configurations were based on Caltrans Standard Plans, and the scope of research was to compare the experimental findings with the design method described in the NCHRP Report 611 as well as to formulate preliminary recommendations for Caltrans practice. A relatively flexible pipe and a stiff box-shaped specimen embedded in dense sand were tested in the centrifuge at the Center for Geotechnical Modeling at University of California, Davis and were subjected to a set of broadband and harmonic input motions. Responses were recorded in the soil and in the embedded structures using a dense array of instruments. Measured quantities included specimen accelerations, bending strains, and hoop strains; soil accelerations, shear-wave velocities, settlements, and lateral displacements; and accelerations of the centrifuge's shaking table. This data paper describes the tests and summarizes the generated data, which are archived at DesignSafe.ci.org (DOI: 10.17603/DS2XW9R) and are accessible through an interactive Jupyter notebook
An Assessment to Benchmark the Seismic Performance of a Code-Conforming Reinforced-Concrete Moment-Frame Building
This report describes a state-of-the-art performance-based earthquake engineering methodology
that is used to assess the seismic performance of a four-story reinforced concrete (RC) office
building that is generally representative of low-rise office buildings constructed in highly seismic
regions of California. This âbenchmarkâ building is considered to be located at a site in the Los
Angeles basin, and it was designed with a ductile RC special moment-resisting frame as its
seismic lateral system that was designed according to modern building codes and standards. The
buildingâs performance is quantified in terms of structural behavior up to collapse, structural and
nonstructural damage and associated repair costs, and the risk of fatalities and their associated
economic costs. To account for different building configurations that may be designed in
practice to meet requirements of building size and use, eight structural design alternatives are
used in the performance assessments.
Our performance assessments account for important sources of uncertainty in the ground
motion hazard, the structural response, structural and nonstructural damage, repair costs, and
life-safety risk. The ground motion hazard characterization employs a site-specific probabilistic
seismic hazard analysis and the evaluation of controlling seismic sources (through
disaggregation) at seven ground motion levels (encompassing return periods ranging from 7 to
2475 years). Innovative procedures for ground motion selection and scaling are used to develop
acceleration time history suites corresponding to each of the seven ground motion levels.
Structural modeling utilizes both âfiberâ models and âplastic hingeâ models. Structural
modeling uncertainties are investigated through comparison of these two modeling approaches,
and through variations in structural component modeling parameters (stiffness, deformation
capacity, degradation, etc.). Structural and nonstructural damage (fragility) models are based on
a combination of test data, observations from post-earthquake reconnaissance, and expert
opinion. Structural damage and repair costs are modeled for the RC beams, columns, and slabcolumn connections. Damage and associated repair costs are considered for some nonstructural
building components, including wallboard partitions, interior paint, exterior glazing, ceilings,
sprinkler systems, and elevators. The risk of casualties and the associated economic costs are
evaluated based on the risk of structural collapse, combined with recent models on earthquake
fatalities in collapsed buildings and accepted economic modeling guidelines for the value of
human life in loss and cost-benefit studies.
The principal results of this work pertain to the building collapse risk, damage and repair
cost, and life-safety risk. These are discussed successively as follows.
When accounting for uncertainties in structural modeling and record-to-record variability
(i.e., conditional on a specified ground shaking intensity), the structural collapse probabilities of
the various designs range from 2% to 7% for earthquake ground motions that have a 2%
probability of exceedance in 50 years (2475 years return period). When integrated with the
ground motion hazard for the southern California site, the collapse probabilities result in mean
annual frequencies of collapse in the range of [0.4 to 1.4]x10
-4
for the various benchmark
building designs. In the development of these results, we made the following observations that
are expected to be broadly applicable:
(1) The ground motions selected for performance simulations must consider spectral
shape (e.g., through use of the epsilon parameter) and should appropriately account for
correlations between motions in both horizontal directions;
(2) Lower-bound component models, which are commonly used in performance-based
assessment procedures such as FEMA 356, can significantly bias collapse analysis results; it is
more appropriate to use median component behavior, including all aspects of the component
model (strength, stiffness, deformation capacity, cyclic deterioration, etc.);
(3) Structural modeling uncertainties related to component deformation capacity and
post-peak degrading stiffness can impact the variability of calculated collapse probabilities and
mean annual rates to a similar degree as record-to-record variability of ground motions.
Therefore, including the effects of such structural modeling uncertainties significantly increases
the mean annual collapse rates. We found this increase to be roughly four to eight times relative
to rates evaluated for the median structural model;
(4) Nonlinear response analyses revealed at least six distinct collapse mechanisms, the
most common of which was a story mechanism in the third story (differing from the multi-story
mechanism predicted by nonlinear static pushover analysis);
(5) Soil-foundation-structure interaction effects did not significantly affect the structural
response, which was expected given the relatively flexible superstructure and stiff soils.
The potential for financial loss is considerable. Overall, the calculated expected annual
losses (EAL) are in the range of 97,000 for the various code-conforming benchmark
building designs, or roughly 1% of the replacement cost of the building (3.5M, the fatality rate translates to an EAL due to
fatalities of 5,600 for the code-conforming designs, and 66,000, the monetary value associated with life loss is small,
suggesting that the governing factor in this respect will be the maximum permissible life-safety
risk deemed by the public (or its representative government) to be appropriate for buildings.
Although the focus of this report is on one specific building, it can be used as a reference
for other types of structures. This report is organized in such a way that the individual core
chapters (4, 5, and 6) can be read independently. Chapter 1 provides background on the
performance-based earthquake engineering (PBEE) approach. Chapter 2 presents the
implementation of the PBEE methodology of the PEER framework, as applied to the benchmark
building. Chapter 3 sets the stage for the choices of location and basic structural design. The subsequent core chapters focus on the hazard analysis (Chapter 4), the structural analysis
(Chapter 5), and the damage and loss analyses (Chapter 6). Although the report is self-contained,
readers interested in additional details can find them in the appendices
Present and future resilience research driven by science and technology
Community resilience against major disasters is a multidisciplinary research field that garners an ever-increasing interest worldwide. This paper provides summaries of the discussions held on the subject matter and the research outcomes presented during the Second Resilience Workshop in Nanjing and Shanghai. It, thus, offers a community view of present work and future research directions identified by the workshop participants who hail from Asia â including China, Japan and Korea; Europe and the Americas
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