SEMINAR
SERIES: 2003
DEPARTMENT OF CIVIL
ENGINEERING AND ENGINEERING
MECHANICS
Fall Semester
September 11, 2003 (Thursday) Room 633 Mudd
2:30-3:30 pm
Gregor Vilkner, Graduate research Assistant, CEEM
Glass Concrete Thin Sheets Reinforced with Prestressed Aramid Woven Fabrics
March 20, 2003 (Thursday)
2:30 p.m. - 3:30 p.m. (Mudd 633)
Prof. Roger Ghanem
The Johns Hopkins University
April 17, 2003 (Thursday)
1:30-2:30 p.m. (633 Mudd)
Connie Crawford, Vice Pres. & Dep. Chief Engineer, MTA
Reconstruction of the Subway after 911
Abstracts
A New Method for Nonlinear and Nonstationary Time Series
Analysis and Its Applications
Dr. Norden E. Huang
Senior Fellow
NASA Goddard Space Flight Center
Greenbelt, MD 20771
A new method for analyzing nonlinear and nonstationary data has been developed.
The key part of the method is the Empirical Mode Decomposition method with
which any complicated data set can be decomposed into a finite and often
small number of Intrinsic Mode Functions (IMF). An IMF is defined as
any function having the same numbers of zero-crossings and extrema, and also
having symmetric envelopes defined by the local maxima and minima respectively.
The IMF also admits well-behaved Hilbert transform. This decomposition
method is adaptive, and, therefore, highly efficient. Since the decomposition
is based on the local characteristic time scale of the data, it is applicable
to nonlinear and nonstationary processes. With the Hilbert transform,
the Intrinsic Mode Functions yield instantaneous frequencies as functions
of time that give sharp identifications of imbedded structures.
The final presentation of the results is an energy-frequency-time distribution,
designated as the Hilbert Spectrum. Classical nonlinear system models
are used to illustrate the roles played by the nonlinear and nonstationary
effects in the energy-frequency-time distribution. Examples of this
new data analysis method will be presented for diverse applications including
earthquake data, such as from the 1999 Chi-Chi earthquake in Taiwan, climate
data, and nondestructive health monitoring of bridges.
Error Budgets for the Validation of Complex Predictive Models
Prof. Roger Ghanem
The Johns Hopkins University
The validation of predictive models entails determining whether a certain
model is suitable to a certain task. The suitability criterion is construed
as quantifying the closeness of the model-based predictions to either existing
or potential experimental evidence.
A constructive approach is adopted in this presentation to the task of Validating
predictive models. A mathematical framework is delineated that permits
the formulation of meaningful questions in connection with the validation
problem. These questions may relate to the validity of a certain model, or
to whether a non-validated model can be validated, and if so then at what
expense. In this latter case, computable actions to ensure validation
are developed.
The mathematical framework permits the formulation of the problem as that
approximation over a product measure space. This framework permits the
extension of concepts from adaptive error estimation as developed for PDE's
to the realm of model validation. Refinement of prediction accuracy,
through mesh refinement, adaptive time-stepping, or adaptive sampling, for
example, is now supplemented by a refinement of the data upon which the model
is based.
This framework permits the blending of experimental data with model-based
data. This has significant consequence on the analytical certification of
components and systems, as well as on optimizing the allocation of resources
between experimental and computational efforts.
Stiffness at Small Strains
of Stiff Geomaterials Related to Some Major Construction Projects in Japan
Prof. Fumio Tatsuoka, University of Tokyo
The stiffness at small strains is often one of the key design parameters
in geotechnical construction projects. The importance of small strain
measurement is illustrated through three major projects in Japan: Trans-Tokyo
Bay Project, Akashi-kaikyo Suspension Bridge and Bay bridge.
In the Trans-Tokyo Bay project, the stiffness values of different types
of cement-mixed soil, mixed in-place and mixed in plant, were evaluated by
laboratory triaxial compression tests measuring axial strains locally from
less than 0.001 % to large strains at the residual conditions at the design
stage and by both field shear wave velocity measurements in the completed
structures and triaxial tests on core samples retrieved from the site during
construction. In the construction projects of the foundations for the
World's longest suspension bridge and a suspension bridge in the Tokyo Bay,
the stiffness of sedimentary soft rocks was evaluated at the design stage.
The observed settlements of the foundations were analyzed by using stiffness
values from several laboratory and field testing methods. In the presentation,
the stress-strain properties of cement-mixed soil and sedimentary soft rock
are compared. It will also be shown based on these projects and others
that the stiffness that is usually operated in the field is generally small
and it is necessary to obtain design values by taking into account the non-linearity
due to strain and pressure.
Probabilistic Benefit-Cost Analysis for Earthquake
Damage Mitigation: Evaluating Measures for Apartment Houses in Turkey
Guillermo Franco
Graduate Research Assistant, Department of Civil Engineering and Engineering
Mechanics, Columbia University
Abstract: In the wake of the 1999 earthquake destruction in Turkey, the urgent
need has arisen to evaluate the benefits of loss mitigation measures that
could be undertaken to strengthen the existing housing stock. A cost benefit
analysis for the implementation of various seismic retrofitting measures
is performed on a common and vulnerable type of apartment building located
in Istanbul. The analysis was performed probabilistically, through the development
of fragility curves of the structure in its different retrofitted configurations.
By incorporating the probabilistic seismic hazard for the region, expected
losses were obtained for arbitrary time-horizons. By including realistic
cost estimates of the retrofitting schemes and costs of direct losses, one
can estimate the benefit of the retrofitting measures in present day values.
A sensitivity analysis was performed to determine the effects of varying
cost parameters and also the assumed cost of human lives. In this case study,
the analysis implies that, even when considering only direct losses, all
of the retrofitting measures considered are very desirable for all but the
very shortest time-horizons. This methodology can be extended to an entire
region by incorporating additional structure types, soil types, retrofitting
measures etc. It is hoped that this work can support some of the most urgent
decisions and serve as a benchmark for more realistic and targeted cost-benefit
analyses.
The ConGlassCrete Projects: Towards Certification of Waste Glass as Aggregate and Pozzolan in Concrete Products
Prof. Ewan Byars, University of Sheffield, UK
The Centre for Cement and Concrete at the University of Sheffield
is leading the collaborative efforts of 24 partners in the UK who are
seeking ways to maximise the use of waste glass in concrete. The
main effort is in the area of waste container glass from bottle-bank
and pub and club collections, however the projects have also extended
their work into waste flat glass, windscreens, light bulbs, flourescent
tubes
and glass fibres.
Two main research areas - glass pozzolanicity and glass
alkali-silica-reactivity are under investigation. Pozzolanic behaviour
has been found to be fairly consistent across all glass waste streams
examined and the projects are moving towards gaining generaic
certification for the materials in this respect. Alkali-silica
reactivity is more complex, as differences in reactivity have been
found when different glass colours, particles size ranges and cements
have been used. However, the use of ASR suppressants has been
extremely successful.
On a practical production note, in virtually all of the 20 full-scale
sub-projects conducted at precast concrete plants, the concrete
products containing glass as aggregate or pozzolan passed product
compliance testing. As a result of this, several products are
being selected for 3rd-Party certification.
Design of the World's Tallest Buildings - Petronas Twin
Towers at Kuala Lumpur City Centre
Mr. Leonard M. Joseph, Thornton-Tomasetti Engineers, New York, NY
This presentation on the twin 451.9m (1483 ft.) tall, 88 story towers in
Kuala Lumpur, Malaysia, will highlight key design and construction features of
the unusual foundations of these buildings, currently the tallest in the world.
Irregular bedrock required extensive pre-design, analysis and construction
attention. Elaborate borings and probes established profiles and soil
characteristics. Detailed 3-D finite element models set the variations in
barrette lengths, up to 130 m (426 ft.) deep, to avoid differential settlement
without bearing on rock. Skin grouting, cavity grouting and slump zone
grouting further reduced settlements. Other foundation features include
massive concrete mats, perimeter slurry walls 1 km (0.6 mi.) long and 20 m (66
ft.) deep, and a pressure relief system under low-rise portions of the project.
The superstructure design considered wind effects on load and occupant
comfort. A high-strength concrete cast-in-place core, perimeter columns
and ring beams economically carry vertical loads and provide lateral load
stiffness with high inherent damping for occupant comfort. Steel beams on metal
deck slabs provide economy, fast erection and adaptability to future changes in
openings and loads. The project also features a unique Skybridge spanning
58.4 m (190 ft.) between towers at levels 41 and 42, and a tall pinnacle of
structural stainless steel crowning each tower.
Leonard M. Joseph, P.E. is a
Vice President and Principal of Thornton-Tomasetti Engineers, a 360-person
organization providing design and engineering services for commercial,
institutional and industrial building projects. A civil and structural engineer, he holds a Bachelor of Science
degree from Cornell University, and Master of Science and M.B.A. degrees from
Stanford University.
Mr. Joseph is a Registered
Professional Engineer in the states of New York, Washington and California, a
Structural Engineer in California and a member of The American Society of Civil
Engineers (ASCE).
Mr. Joseph’s experience with
Thornton-Tomasetti Engineers includes the design of the 452 m-tall-Petronas Twin
Towers (tallest buildings in the world) at Kuala Lumpur City Centre in
Malaysia, a 9 million sq. ft. mixed‑use project, the 54-story steel-skin One
Mellon bank Center in Pittsburgh, and the 50-story Chifley Tower in Sydney with
an optimized irregular frame. Mr.
Joseph’s long-span project experience includes Arrowhead Pond Arena in Anaheim,
CA, the College of Staten Island gym and pool, a submarine factory with
200-foot spans, numerous aircraft hangars and several pedestrian bridges. He is currently completing Pacific Bell
Park, the new home of the San Francisco Giants baseball team.
Mr.
Joseph has taught steel and concrete design at New York Institute of Technology
and has co-authored the book Exposed Structure in Building Design as
well as numerous technical articles appearing in Civil Engineering Magazine,
the Journal of Wind Engineering and Industrial Aerodynamics, Building
Structural Design Handbook, The Encyclopedia of Science & Technology,
and international conference proceedings.
Impacts of Strain Localization and Specimen Heterogeneity on
the Behavior of Sand
Amy Rechenmacher, Ph.D.
Assistant Professor,
Department of Civil Engineering, The Johns Hopkins
University, Baltimore, MD
It is well known that localized strains, or shear
bands, form in dense sands at peak stress, and that post-failure behavior is
confined within these narrow zones of intense displacement. Thus, to assess true constitutive behavior,
including the evolution to Critical State, quantitative measurements of
deformations associated with the onset and progression of strain localization
must be made. Digital imaging methods
such as Digital Image Correlation (DIC), or Computer Vision and Particle Image
Velocimetry (PIV), have yielded highly accurate local displacement measurements
for fluids and concretes, and are now being applied to sands. Drained, plane strain compression tests were
conducted on dense sands in an apparatus configured to permit visual
observation of in-plane deformations.
Digital images were taken throughout deformation and DIC was used to
quantify local shear band displacements and determine void ratio evolutions to
Critical State. Results suggest that a
unique Critical State void ratio-effective stress relationship is realized only
for sands consolidated from similar deposition void ratios. However, more recent, detailed observations
of the displacement structure within the shear bands strongly suggests that the
previous assumption of displacement linearity needs to be revisited.
The detection and characterization of soil
heterogeneity is significant for the numerical prediction of soil behavior and
in predictions associated with the initiation of bifurcation phenomena. In an effort
to quantify this ever-present heterogeneity, a novel model calibration
technique is currently being developed in which 3-D image-based displacement
measurements of deforming triaxial specimens are assimilated into finite
element predictive models of soil behavior.
Inverse techniques are used to locally vary model parameters until an
optimal match between predicted and measured specimen shapes is obtained. To date, only the linear problem has been
tackled, but the approach shows promise for handling more complex models. It is hoped that eventually the approach
will lead to the development of stochastic models of soil specimens that
account for observed specimen variability.
Dr. Amy Rechenmacher received her B.S. in Civil Engineering from Iowa State
University, her M.S. from Cornell University, and Ph.D. from Northwestern
University. In between M.S. and Ph.D. degrees, Dr. Rechenmacher
worked in geotechnical practice, first in geotechnical contracting and then in
geotechnical consulting. Her research
is predominantly experimental, using techniques such as 2- and 3-D digital
imaging methods and X-Ray Computed Tomography (CT), and focuses on localization
in granular materials, constitutive behavior of soils, advanced model
calibration techniques, and probabilistic characterization of scatter in
geotechnical data.
Simulating Microstructure Evolution
Prof. Hong-Hui YU
Mechanical Engineering Department, City College of New York
A solid may change its microstructure or morphology over some time. For examples,
a film may break into droplets, and an interconnect may grow cavities.
Structural evolution, brought about by chemical reaction and mass transport,
driven by diverse thermodynamic forces, is of fundamental importance for
the fabrication, performance and reliability of small structures, such as
integrated circuits and MEMS, whose feature size could be sub-micrometer.
In this talk, the general framework for simulating microstructure evolution,
based on a weak statement, will be described. Two simulations will
be presented. The first example is the delayed fracture in a brittle
solid caused by stress dependent surface reaction. For a small structure
such as a thin film, a conduct line or a micro-beam in MEMS, a small change
in shape may greatly reduce its total lifetime. Simulating the shape
change along with time, finding the threshold condition for failure and estimating
the lifetime are essential to the design of small structures. Here,
a solid corroding gradually by a surface reaction is simulated. The solid
is in addition subject to a mechanical load and loses mass preferentially
at places where stress concentrates, so that atomistically sharp cracks may
nucleate. The second example deals with the pore-grain boundary
separation process ceramic sintering. In the final stage of ceramic
sintering, pores can either move with, or separate
from, grain boundaries. The outcome is critical to the resulting ceramics.
This simulation incorporates two rate processes, grain boundary migration
and surface diffusion, and shows the transient separation process.
Seismic Soil-Structure Interaction: Beneficial or Detrimental?
Prof. George Mylonakis
The City University of New York
The role of soil-structure interaction (SSI) in the seismic response of structures
is re-explored using recorded motions and theoretical considerations.
First, the way current seismic provisions treat SSI effects is briefly revisited.
The idealized design spectra of the codes along with the increased fundamental
period and effective damping due to SSI lead invariably to reduced forces
in the structure. Reality, however, often differs from this view. It is shown
that, in certain seismic and soil environments, an increase in the fundamental
natural period of a moderately flexible structure due to SSI may have a detrimental
effect on the seismic demand imposed to the system, an effect that contradicts
the widely held belief of an always-beneficial role for SSI. Second, a widely
used structural model for assessing SSI effects on inelastic bridge piers
is examined. Using theoretical arguments and rigorous numerical analyses
it is shown that indiscriminate use of ductility concepts and geometric relations
may lead to erroneous conclusions in the assessment of seismic performance.
A case study is then presented regarding the role of soil on the collapse
of 18 piers of the elevated Hanshin Expressway in the Kobe Earthquake. Analytical
studies based on recorded motions indicate that the role of soil in the collapse
was double: First, it modified the seismic waves so that the frequency content
of the surface motion became disadvantageous for the particular structure.
Second, the compliance of the foundation altered the vibrational characteristics
of the bridge and moved the system to a region of stronger response. The
associated increase in ductility demand on the piers may have exceeded 100%
as compared to piers fixed at the base. The presented results are in contradiction
with prevailed perceptions of an always-beneficial role of seismic soil-structure
interaction.
Semiactive and Smart Concept Based Schemes in Structural Control
Prof. Akira Nishitani
Waseda University/University of Illinois, Urbana-Champaign
For the last two decades, structural control schemes have been substantially
accepted and integrated into seismic design of civil structures. These schemes
are expected to play more and more significant role at the future stage of
structural engineering. A variety of control technologies have been developed
and practically applied to real structures, in particular to many building
structures in Japan. Among these technologies, semiactive control concept
has recently appealed the attentions of structural engineers as one of the
most promising means for sophisticatedly or smartly protecting structures
against severe earthquakes. Semiactively controlled dampers in particular
are referred to as "smart" dampers. Japan is widely known as a country which
has enthusiastically developed various control philosophies and devices and
implemented them to real structures. There are already several pioneering
practical applications of semiactive or smart damper installations to building
structures in Japan. Semiactive and smart concept in structural control,
together with its full scale implementations in Japan, is discussed.
And the recent research result in regard to semiactive control based on variable
slip-force level dampers is also presented.
Seismic Monitoring of Structures: Current and New Developments
Dr. Mehmet Celebi
US Geological Survey
Seismic monitoring of structural systems constitutes
an integral part of earthquake
hazard reduction programs. Recordings of the acceleration response of
structures have served the scientific and engineering community well and have
been useful in (a) assessing design/analysis procedures, (b) improving code
provisions, (c) correlating the system response with damage and (d) calibrating
the performance of new
applications in design and construction methods.
For the two main
structural instrumentation programs in California, the California Strong-Motion
Instrumentation Program (CSMIP) and the USGS programs, the main objective to
date has been to achieve quantitative measurement of structural response to
strong and possibly damaging ground motions. Thus, the aim has been to
facilitate response studies in order to improve our understanding of the
behavior and potential for damage of structures under the dynamic loads of
earthquakes for purposes of improving design and construction practices. Up to
now, it has not been the objective of either instrumentation program to
create a health monitoring environment for structures.
Recent
needs of structural engineers necessitate the measurement of displacements in
order to assess drift ratios during strong shaking events. In order to achieve
these, two new developments are presented:
(a) application of differential GPS measurements for long-period structures
and (b) a real-time assessment and alarm system based on computation of drift
ratios from double-integrated acceleration measurements. Both of these new
applications can be used for performance evaluation of structures.
Probabilistic Seismic Hazard Estimates in Nevada: Questionable Results and How we Might Fix Them
Prof. John Anderson
University of Nevada-Reno
Abstract: The hazard curves estimated by several probabilistic seismic hazard
analyses in Nevada, including the high-profile analysis of the proposed Yucca
Mountain nuclear waste repository, are not particularly credible. Hazard
curves are, conceptually, the outcome of an experiment where ground motion
is recorded at a single site for a very long time (e.g. >105 years), and
then statistics of extreme values are derived from the data. To test
the low probabilities, one can look for geological structures that would
be different if strong shaking occurred. For instance, in the desert
environment, 10,000 year old, precariously balanced rocks are one such indicator.
In general, the challenge of testing hazard curves takes the problem into
a realm requiring a broad spectrum of Earth sciences. Possible explanations
for the inconsistence of PSHA and geological indicators are 1) ground motion
prediction equations overestimate the ground motions, or 2) uncertainties
are mishandled. Both explanations probably contribute. The second is almost
surely the case, in several ways: a) the use of an ergodic assumption to
estimate standard deviations, b) the assumption that ground motions have
a lognormal distribution about the mean, and c) the treating of epistemic
uncertainties as if they are aleatory.
Uncertainty Quantification of Terascale Engineering Applications: First Step Towards Robust Design
Dr. Steve Wokjiewicz
Sandia National Laboratories
A necessary first step in the robust design and optimization of terascale
engineering models is the quantification of uncertainty in their response.
This uncertainty can arise from a variety of sources including uncertain
inputs, uncertain parameters embedded in the models, and/or uncertainty in
model form. The presentation will discuss the development of tools to perform
the uncertainty assessment in a massively parallel, multiphysics computational
environment and the results of the application of such tools to a large-scale
engineering analysis problem.
Steve Wojtkiewicz received his Ph. D. in aeronautical and astronautical
engineering from the University of Illinois at Urbana-Champaign in 2000 after
which he joined Sandia National Laboratories as a member of the technical
staff in the structural dynamics research department. His research areas
include random vibration techniques for nonlinear systems, computational
stochastic mechanics, the development and application of methods for uncertainty
quantification of terascale computational engineering systems, and optimization
under uncertainty/robust optimization algorithms.