Seismic
Responses of Subway Structures in Liquefiable Soils
and the Mitigation
Huabei Liu (host: Prof. Ling)
Assistant Professor, Department of
Civil Engineering
City University of New York
The construction
of subway or other tunnels in liquefiable
soils sometimes is inevitable. Severe damages to the underground
structure may
occur during strong earthquake due to the excessive deformations of
soils or
even floatation of the underground structure itself. The seismic
responses of
subway structures in liquefiable soils and the possible damages were
investigated using dynamic centrifuge tests and fully coupled Finite
Element
analysis. The possible mechanisms of the seismic responses were
identified. Some
possible mitigation schemes were studied and a simplified analysis
method was
also proposed for the in-plane response of subway structures. The
necessary
further research is finally discussed.
Dr. Huabei Liu is an assistant professor
at the City University of New York. Previously, he was a geotechnical
faculty at the Department of Civil Engineering, Tsinghua University (August 2003-2007).
He obtained his Ph.D. in Geotechnical Engineering from the Department
of Civil
Engineering and Engineering Mechanics at Columbia University
in December, 2002, and worked for a brief period as postdoc research
scientist. Dr. Liu
works mainly in the field of geosynthetic-reinforced soil structures,
soil
liquefaction and constitutive modeling of geomaterials. He now serves
as a
member in the Technical Committee of Soil-Structure Interaction (TC 38)
of the
International Society of Soil Mechanics and Geotechnical Engineering
(ISSGE).
September 25, 2007
Multi-Objective Decision Support Model for Maintenance and Repair Strategies for A Bridge Network
Huang-Chih (Jerry) Wu (advisors: Prof. Testa & Prof. Garvin)
Ph.D. Candidate, CEEM, Columbia University
Over the last decade, various bridge
management systems (BMS) have been developed to assess strategies for
maintenance and repair of bridges with the aim of minimizing cost while
prolonging life. Generally, these have dealt with management of
individual bridges or projects within a network rather than treating
the network as a whole. In this work, a computational model is
developed to aid in identifying optimal strategies for maintenance and
repair in a group of bridges viewed as a network with the threefold
objectives of maximizing bridge service life, minimizing maintenance
and repair costs, and minimizing user travel time delay. These three
objectives are not expressed by linear equations nor are they
formulated in analytical forms. A genetic algorithm approach for
the multi-objective optimization is detailed. Results are
explored for several idealized networks and for two actual NYC bridge
networks- the Henry Hudson Parkway and the Brooklyn-Queens Expressway.
October 2, 2007
Integrated Processes in Structural Engineering
Dr. Gregor Vilkner (host: Prof. Meyer)
Thornton Tomasetti, New York
The
structural engineering profession has recently become faced with two major
challenges that evolve less around mechanics and design philosophies, but
around the way data generated for complex projects is managed and how
structural systems and design results are communicated with the other participants
on the design team.
As
the AEC industry strives to establish integrated knowledge exchange protocols
utilizing building information models (BIMs), structural engineering practices
of all sizes will profit from the ability to effectively communicate with the
design team supported by an integrated structural design process. At Thornton
Tomasetti, custom tools are developed to automate the exchange of structural
design data between 2D and 3D analysis models and BIMs. These tools are unique
because they allow the engineer to manage partial models and data sets as
independent sub-systems of complete virtual models. These sub-systems are often
described in plan or elevation, while their counter parts reside in the 3D
setting of the overall BIM.
Custom
automation of processes at Thornton Tomasetti helps to meet deadlines, exceed
expectations of clients, and increases the quality of the work product. We cite
few examples illustrating custom usage of application programming interfaces
(APIs) and address typical challenges met when pursuing in-house development
projects. The case studies include the utilization of conventional CAD
documents as basic structural information models (SIMs), the automatic assembly
of structural elements of complete towers in a BIM, and efficient bent
management assisting the design process of stadiumlike structures.
October 9, 2007
11:00-12:00, Lerner Hall 555
Burmister Lecture
Seismic Design and Analysis of Embankment Dams: The State of Practice
Dr. William F.Marcuson,
III
President, ASCE
&
U.S.Army Engineer Waterway Experiment Station (retired)
This
Lecture traces the development of the state of practice in seismic
design and analysis of embankment dams, starting in the mid 1960's and
continuing through
2000. The key issue, evaluation of earthquake -induced liquefaction of
saturated loose cohesionles material, will be discussed, with emphasis
on key components of the problem. Remediation methods for fixing
existing embankment dams judged to be unsafe, should the "design"
earthquake occur, are
summarized. Gaps in our knowledge are identified and he will sketch a
vision regarding future developments in permanent deformation analyses,
site characterization, remediation and ground motions.
Dr. William
F. Marcuson III is President of the American Society of Civil Engineers
(ASCE) and is one of the nation.s leading civil engineers. He holds
degrees in civil engineering from The Citadel, Michigan State
University and North Carolina State University. He has received five national
awards from ASCE, including the Norman Medal, civil engineering's
oldest honor. In 1995 he was honored by the National Society of
Professional Engineers as their Federal Engineer of the Year. His
career included research and administrative positions at the U. S. Army
Engineer Waterways Experiment Station, where he served as Director of
the Geotechnical Laboratory for nearly 20 years, prior to his
retirement in 2000. He is the only engineer to be named the Corps of
Engineer's Engineer of the Year twice (1981 and 1995), and he was
honored by the Corps as their Civilian of the Year in 1997. He was
elected to the National Academy of Engineering in 1996 for his
contributions to the design and analysis ofembankment dams.
October 16, 2007
The Real Story of Project Management
Prof. Alex Laufer (host: Prof. Meyer)
Israel Institute of Technology
The project method has evolved from a
specialty into the central task of middle management. To the
hundred of thousands of traditional project managers (e.g., in
construction and aerospace), one must add the millions of new project
managers representing diverse functions in organizations, encompassing
nearly the whole range of white-collar workers. Paradoxically, this
sharp increase in the popularity of the project method has been
accompanied by an increasing dissatisfaction with current project
management practices and results. In the seminar I will discuss the
required reform needed in project management research and practice, as
well as my own research methodology. In particular I will discuss my
approach for developing a "theory of practice".
October 23, 2007
Integration of Multiscale and Stochastic Modeling on Advanced Computational
Reliability
Prof. X. Frank Xu
Dept of Civil, Envir & Ocean Engrg
Stevens Institute of Technology
Size of complex synthetic and nature materials spans many length scales
from nano- and micro-scale electronic-mechanical systems, to meso-scale ceramic
components, to macro-scale concrete, and to mega-scale earth faults. Failure
prediction of complex material systems involving multiscale, nonlinearity, and
uncertainties presents one of most critical engineering challenges. Multiscale
modeling and uncertainty quantification are two most active research fields,
while currently being pursued separately. Integration of the two, i.e.
multiscale stochastic modeling (MSM), is envisioned as an emerging research
frontier. The
essential characteristic of the MSM is its
unique role serving as a functional operator to upscale uncertainty
information, rather than mean values as implicitly undertaken by deterministic
multiscale models. Incorporating of stochastic processes into multiscale modeling
is expected to generate an entirely new class of models, and reshape the whole
scenario of multiscale research. By
using elliptic problems as a paradigm, a framework of
multiscale stochastic finite element method (MsSFEM) has been developed to
initialize the MSM research from a mathematical perspective. Further
development of the MSM demands specific tailoring of mathematical exploration
to well-defined physics. A famous case of the MSM on brittle materials
is the Weibull theory offering a close-form solution for scale-crossing failure
probability. For non-brittle materials,
extreme value statistics and large size
problems pose gigantic challenges to existing monoscale stochastic models, and
multiscale stochastic approaches become essential.
This talk will present
our recent work in developing the MSM, which includes characterization of
random materials, stochastic variational principles for boundary value
problems, numerical simulation of stochastic damage and crack propagation, and MsSFEM.
The potential impact to relevant fields and applications will also be
discussed.
October 30, 2007
Inter-school Lab, 750 CEPSR
Maurice Biot Lecture
True Triaxial Testing and the Failure of Rocks
Prof. John W. Rudnicki
Department of Civil and Environmental Engineering
and Department of Mechanical Engineering
Northwestern University
The vast majority of
tests on rocks have been done in axisymmetric configurations in which
two of the principal stresses are equal. This severely limits the
deviatoric stress states that are accessible and makes it difficult to distinguish between various predictions of failure
stress and the orientation of the failure plane. Although K. Mogi did
pioneering work on true triaxial testing (all three principal stresses
are different) in the 1960.s, there has been little systematic work on this subject
since then. Recently, however, Haimson and coworkers have
conducted a series of true triaxial tests on several rock types. This
talk will describe work in progress to interpret these data to gain
additional insight into rock failure and to compare observations with
predictions of failure, including those from the theory of localization
of deformation, and models of inelastic deformation of rock.
Biographical Sketch After
earning his undergraduate and graduate degrees in engineering at Brown
University, John W. Rudnicki was a postdoctoral research fellow in
geophysics at Caltech for 18 months, and then Assistant Professor in
the Department of Theoretical and Applied Mechanics at the University
of Illinois in Urbana-Champaign for three years. In 1981, he
moved to Northwestern University where he is now Professor of Civil and
Environmental Engineering and Mechanical Engineering. His research has
been primarily in the inelastic behavior and failure of geomaterials,
particularly in the effects of coupling between deformation and fluid
diffusion, in connection with applications to the mechanics of
earthquakes, energy storage and recovery and geological sequestration
of CO2. Recently, he has also developed a popular undergraduate course
on the mechanics of sports. He received the 2006 Biot Medal from the
ASCE for "For his fundamental contributions to the mechanics of porous
media and its applications to rock mechanics and geophysics."
November 6, 2007
(Election Day)
November 5, 2007 (Monday) but, also the University Holiday
A Unified Effective Stress Concept for Variably-Saturated
Soil
Prof. Ning Lu
Division of
Engineering, Colorado
School of Mines
A
unified effective stress concept based on the suction stress characteristic
curve (SSCC) for variably-saturated soil is discussed. Particle-scale
equilibrium analyses are employed to distinguish three types of soil interparticle
forces: (1) active forces transmitted through the soil grains (Terzaghi’s); (2)
active forces at or near interparticle contacts (physicochemical); and (3)
passive, or counterbalancing, forces at or near interparticle contacts (Born’s
and steric). It is proposed that the second type of forces, which includes
physicochemical forces, cementation forces, surface tension, and the force
arising from negative pore-water pressure, can be conceptually combined into a
macroscopic stress called suction stress. Suction stress characteristically
depends on degree of saturation, or soil suction, thus paralleling
well-established concept of the soil–water characteristic curve in soil physics.
The existence and behavior of the SSCC are experimentally validated by
considering unsaturated shear strength and volumetric behavior data for a
variety of soil types in the literature. The characteristics and practical determination
of the SSCC are demonstrated. A closed form equation for predicting the
suction stress for all soils is found. A case study of shallow landslide
initiation induced by heavy rainfalls in Seattle
area illustrates that variation in suction stress can well reconcile the
spatial and temporal characteristics of the event. Suction stress provides a
potentially simple and practical means to describe the state of stress in
unsaturated soil.
Biographical Sketch Ning Lu is professor of engineering at Colorado
School of Mines and the director of the joint CSM/USGS Geotechnical Research
Laboratory. He obtained a doctorate degree in engineering science from the Johns Hopkins
University in 1991. Prior
to joining Colorado School of Mines in 1997, he worked as a scientist at
Disposal Safety Inc., and as a hydrologist at the US Geological Survey. He has
been working on challenging engineering problems in chemical transport in clayey
soil, underground nuclear waste isolation, residential house foundation damage by
expansive clays, and, most recently, precipitation-induced shallow landslides.
His primary research interests are to seek common threads among soil physical
phenomena including fluid flow, chemical flow, heat transfer, stress, and
deformation, and to build bridges from atomic-scale potentials to particle-scale
forces and engineering-scale stresses in soil. He is the senior author of the
text book “Unsaturated Soil Mechanics” published by John Wiley and Sons.
Joint CEEM-ME Seminar (November 9, 2007)
Mudd 227, 11 am
Partition
of Unity Finite Elements for Electronic-Structure Calculations in Molecules and
Crystalline Solids
by Prof. N. Sukumar (Civil Eng., UC Davis)
contact Prof. Xi Chen for more details or visit
ME website
Over
the past few decades, the planewave pseudopotential (PW) method has established
itself as the method of choice for large, accurate quantum-mechanical
calculations in solids and liquids. However, due to its global Fourier basis,
the PW method suffers from substantial inefficiencies in parallel
implementation and in problems involving localized states. Modern real-space
methods such as finite-differences (FD), finite elements (FE), and wavelets,
resolve these problems but have until now required a much larger number of
basis functions to attain the required accuracy. In this talk, I will present a
new real-space finite element method to solve the Kohn-Sham equations of
density functional theory. We employ partition-of-unity (PU) enrichment
techniques to build the known atomic physics into the FE basis, thereby
substantially reducing the degrees of freedom required. Higher-order finite
elements are used to discretize the parallelepiped unit cell, and we use
Dirichlet boundary conditions for atoms and molecules and Bloch-periodic boundary
conditions for crystalline solids. The enrichment functions are pseudoatomic
wavefunctions, which are product of radial Schrodinger solutions (computed
using a spectral FE solver) and spherical harmonics. Our initial results for
the energy eigenvalues show order-of-magnitude improvements relative to current
state-of-the-art PW and adaptive-mesh (AMR) FE methods for systems involving
localized states such as d- and f-electron systems.
November 13, 2007
Prof. Lofti A. Zadeh (host: Prof. Dasgupta)
3:00-5:00 pm, Davis Auditorium
CANCELLED
November 20, 2007
Strategies to improve accuracy and
efficiency of numerical methods for the solution of forward and inverse vibro-acoustic
problems
John C. Brigham (host: Prof. Betti)
Ph.D. Candidate, Department of Civil
and Environmental Engineering, Cornell University
A particular difficulty in the vibration analysis of soft
tissues is the relatively high wave numbers which arise in the governing
Helmholtz equations. These high wave
number problems have an added error component for a given discretization, in
addition to the approximation error, which occurs when using Galerkin weak-form
finite element methods. However,
higher-order finite element approximations have been shown to significantly
reduce this additional solution error. Furthermore, by applying spectral element
techniques, the computational difficulties associated with high-order finite
elements, such as Runge’s phenomenon and matrix ill-conditioning, can be
avoided. Unfortunately, these modeling
techniques are, in general, still too computationally expensive to afford the
model-updating approaches commonly applied to inverse characterization problems
in biomechanics. Alternatively, the
model reduction technique of proper orthogonal decomposition (POD) can be used
to derive a reduced-dimension set of basis functions from a previously obtained
set of simulated and/or experimental field measurements. For a given order, these basis functions are
the optimal set, in an average sense, for representing the field data. Therefore, the basis is expected to produce
an accurate and efficient numerical representation of the system, provided
sufficient information exists in the field data. By combining both spectral element and POD
techniques within a model-updating inverse characterization strategy, one can
obtain accurate solution estimates with a reasonable computational
expense. In this talk I will present
both spectral element and POD formulations for acoustic and structural
vibration analysis. Examples will be
presented, within the context of model-updating solution approaches to biomechanics
inverse problems, to display the practical applicability of these techniques in
improving both the accuracy and efficiency of solutions for the governing
Helmholtz equations.
November 27, 2007
Inter-school Lab, 750 CEPSR
CONCRETE VAULTING IN IMPERIAL ROME:
A STRUCTURAL ANALYSIS OF THE GREAT HALL OF TRAJAN.S MARKETS
Renato Perucchio, Dott. Ing., Ph.D. (host: Prof. Betti)
Professor of Mechanical Engineering
University of Rochester, Rochester, New York
The Great Hall occupies a preeminent position within the Trajan's
Markets, the imperial building complex overlooking the Forum of Trajan
in Rome. Built between the years 98 and 117 AD and essentially intact
in all its structural elements, the Great Hall is one of the earliest
surviving examples of a free-standing cross-vaulted halls of major
dimensions built entirely in Roman pozzolanic concrete (opus
caementicium). The vault itself, resting on travertine blocks and
laterally supported by contrasting arches, differs considerably in its
structural design from monumental cross vaults in opus caementicium
built in Rome after the Great Hall. The structural analysis of the
vault and of the supporting system is of fundamental importance to our
understanding of the design paradigms adopted by Roman engineers for
monumental concrete vaulted structures. As part of an
interdisciplinary research conducted with the University of University
of Rome "La Sapienza" and the Museums of the Imperial Fora in Rome, we
are investigating the structural differences in the vaults of the Great
Hall and of the Frigidarium of the Baths of Diocletian (298-306 AD).
Results suggest that the design of the cross vaults evolved in direct
response to structural problems similar to those found in the Great
Hall.
December 4, 2007
Geographic Information Systems for Geoseismic Hazard Assessment
Dr. Sissy Nikolaou
Mueser Rutledge Consulting Engineers, New York
Geographic Information Systems (GIS)
have emerged during the past decade to a software environment for
storing, displaying and organizing large inventories of spatial
information. The seminar presents an integrated GIS developed to
perform seismic hazard and risk assessment. The system can perform
complex interactive
computations which would be difficult and time-consuming to carry out manually, such as:
. deterministic and probabilistic earthquake hazard analysis
. evaluation of different ground motion and seismic source models
. effects of local geology
. generation of design-compatible time histories; and
. damage assessment of spatially distributed structural systems
An application for the New York City metropolitan area demonstrates
that despite the scarcity of recorded data, incomplete knowledge of
seismic
wave propagation characteristics, and sometimes insufficient geologic
data, it is possible to arrive at a rational estimate of the seismic
risk potential in a probabilistic manner, combining available
information and uncertainties in the GIS environment.
December 11, 2007
Portable Air Cleaners: The good, the
bad, and the ugly
Prof. Jeffrey Siegel (host: Prof. Taylor)
Department of Civil, Architectural, and Environmental Engineering
The
University of Texas at Austin
Americans are indoor
creatures, spending 18 hours inside for every hour outside.
Interior environments are also generally more polluted than outdoor
environments and risks to human health from indoor air generally dwarf
those from other environmental media. In response to these risks,
American consumers are presented with a wide variety of products that
purport to purify indoor air. Portable air cleaners are a $500
million annual business in the United States and approximately 10% of
American homes have a portable air cleaning device. Ionizing air
purifiers, a popular air cleaning technology, operate very quietly and
consume little energy. However, they typically have insufficient
air flow to have a substantial impact on indoor particle levels, and
many ionizers generate ozone, a respiratory irritant and oxidant, as a
byproduct of their operation. In this research, we measured ozone
generation, size-resolved particle removal efficiencies (10 nm, 5µ m),
and clean air delivery rates for seven portable ion generators, six
HEPA filters, a portable electrostatic precipitator, and an ozone
generator. The ionizing air cleaners were relatively ineffective
at removing particles from air, and exhibited ozone emissions
comparable to uncontrolled laser printers and photocopiers (0.75 . 4.1
mg/hr). Such emission rates will lead to elevated indoor ozone
concentrations that can cause health risks, particularly for sensitive
populations, and can lead to ozone-initiated chemistry that facilitates
the formation of ultrafine particles and gas-phase byproducts.
Laboratory experiments, as well as a field investigation, confirm that
ozone-generating air cleaners can generate more fine and ultrafine
particles than they remove, especially in the presence of unsaturated
compounds, such as those found in air fresheners, cleansers, and other
fragranced consumer products. These results suggest caution in
the use of ozone-generating air cleaners in indoor environments.
links
Professor
Raymond D.
Mindlin
Fourth Biot
Conference on Poromechanics,
2009