Computational Methods for Modeling Interior and Exterior Wave Propagation
M. N. Guddati
11/99, ongoing
Wave propagation is encountered in countless problems of practical importance
such as nondestructive evaluation, earthquake engineering, seismology, and medical
imaging. In spite of its immense importance and extensive research performed,
current approaches to modeling wave phenomenon still suffer from several shortcomings
related to computational efficiency and accuracy. This project is aimed
at devising new and efficient modeling techniques that would result in highly
accurate solutions with relatively low computational cost. Most recent
results from this research are related to dispersion-reducing finite element
methods and absorbing boundaries.
Investigation of Tip-Screenout Mechanisms in Hydraulic Fracturing
Schlumberger Oilfield Services
$67,171
8/00 to 12/01
Hydraulic fracturing has been widely used in increasing the productivity of
oil and gas wells over the last century and continues to be the most effective
technique for production enhancement. In spite of the extensive experience,
the hydraulic fracturing process is still a mystery, with several critical aspects
not properly understood. One of such important phenomena is tip-screenout,
defined as the arrest of the fracture resulting from dehydration of the slurry.
This has a tremendous impact on the final propped fracture geometry, and thus
on production enhancement. This project is expected to result in an enhanced
qualitative and quantitative understanding of tip-screenout mechanisms.
Multi-Level Computational Modeling of Damage and Failure
Unsponsored
02/00, ongoing
The phenomena of failure and damage of engineering materials span a wide range
of spatial and temporal scales. Recent advances in computing power and
micro-mechanical modeling research make it feasible to investigate the local
behavior of failure and damage of heterogeneous materials with the use of computational
models. However, simulating global mechanisms using micro-mechanics-based
models is not efficient, even when it becomes feasible. This project involves
exploratory investigation of multi-level algorithms to simulate failure and
damage of large heterogeneous systems. On one extreme these algorithms
are expected to emulate homogenized continuum models, and on the other extreme
they emulate detailed micro-mechanical models.
Decision Support for Seismic Performance Evaluation
Abhinav Gupta, John Baugh Jr., and G. Mahinthakumar
National Science Foundation
9/00 to 2/02
The overall goal of this research is to develop formal computational approaches
that support comprehensive decision making in structural engineering.
Specifically, these approaches will be realized in a prototype decision support
system that draws on complementary strengths of the engineer and the computer
in a joint-cognitive system. Its design will be based on three major concepts:
(1) optimization for evaluating alternatives and supporting what-if analyses;
(2) sub-component approach to address structural model synthesis, scalability,
model updating, and uncertainty propagation; and (3) implementation in an object-oriented
framework of high performance distributed computing. A series of simple
and real-life test cases will be used to evaluate the proposed prototype.
Development of Advanced Technologies to Reduce Design, Fabrication and Construction
Costs for Future Nuclear Power Plants
Abhinav Gupta and Ajaya Kumar Gupta
US Department of Energy, Sub-award from Duke Engineering & Services, Marlborough,
MA.
8/99 to 7/02
Numerical and practical difficulties in modeling systems with heterogeneous
structures like building, equipment, and piping by conventional analysis tools
have resulted in excessive conservatism and cost-intensive requirements for
construction, procurement, installation, and maintenance. Computational
and numerical techniques will be developed for synthesizing system models using
heterogeneous sub-system models with varying degree of refinements without sacrificing
solution efficiency needed in analytical simulations. These methods will
account for sub-system interactions and provide flexibility to evaluate effects
of structural changes at design, construction, and operation stages on qualification
requirements for mechanical and electrical equipment. Uncertainty propagation
and model updating will also be studied.
Risk Informed Assessment of Regulatory and Design Requirements for Future Nuclear
Power Plants
Abhinav Gupta and Ajaya Kumar Gupta
US Department of Energy, Sub-award from ABB Combustion Engineering, Windsor,
CT
8/99 to 7/02
Risk-consistent design of structural systems constitutes two important tasks:
allocation of system risk to individual components and development of risk-based
design procedures. In practice, a mixed approach is needed in which certain
structural members are designed within a risk-based framework, whereas the others
are designed in a deterministic framework. However, it requires identification
of interacting components to evaluate critical failure modes and their interdependencies.
These interactions are incorrectly ignored in current practice leading to excessive
conservatism and high costs. Proposed research will develop methods for
(1) identification of interacting components, (2) optimized allocation of system
risk among components, and (3) seismic risk assessment and design.
Center for Nuclear Power Plant Structures, Equipment and Piping (C-NPP-SEP)
Ajaya Kumar Gupta, Professor and Director; Vernon C. Matzen, Associate Professor
and Associate Director; Tasnim Hassan, Assistant Professor; Abhinav Gupta, Assistant
Professor;
Member Organizations and Participants in Dissemination Activities
Calendar 2001
C-NPP-SEP performs research to develop innovative but rigorous solutions to
the structural safety problems of the nuclear power plant buildings and components.
These solutions reduce uncertainty, increase safety and significantly decrease
cost of operating existing plants and building new plants. The Center
currently has nine member organizations, five of them international. The
Center is hosting the 16th International Conference on Structural Mechanics
in Reactor Technology.
Controlled Capacity Joints of SIFCON
J. M. Hanson and N. Krstulovic-Opara
8/96 to 8/00
Resistance of concrete structures to seismic loadings may be improved if certain
regions within elements of the structure were designed to absorb most of the
earthquake damage. In this project, tests are being conducted on specimens
reinforced with a combination of fiber concrete and various types and patterns
of reinforcing bars. Techniques to predict the behavior of these specimens
are also being developed. The Ph.D. dissertation for this project is in
preparation. Present effort is unfunded, but the research originated as
part of an NSF project directed by Professor Neven Krstulovic-Opara.
ASME Code and Ratcheting in Piping Components: Experiments and Analyses
T. Hassan and V. C. Matzen
Center for Nuclear Power Plant Structures, Equipment and Piping, NC State University
1/01 to 12/01
The main goal of this project is to develop an analysis tool for ratcheting
simulation of piping components. This analysis tool can be used to incorporate
ratcheting into the ASME Code in a rational manner. To understand the
ratcheting failure mechanism and incorporate it into the design methodology,
a systematic set of ratcheting data and an improved finite element analysis
program for ratcheting simulation will be developed.
Fatigue Failure of Socket Welded Joints
T. Hassan
Center for Nuclear Power Plant Structures, Equipment and Piping, NC State University
1/01 to 12/01
This research is making efforts to understand the influence of residual stresses
on fatigue crack initiation in socket welds. Residual stresses at welds
because of welding sequence will be estimated through detailed finite
element analyses. Influence of residual stresses on the initiation of
fatigue cracks will be studied. Computed fatigue life will be verified
by comparing with experimental data.
A Unified Approach to Predicting Long Term Performance of Asphalt-Aggregate
Mixtures
Y. R. Kim, R. H. Borden, and Y. Horie
National Science Foundation
9/98 to 8/01
The research objective is to develop test methods and models for predicting
long term performance of asphalt concrete that can account for viscoelasticity,
damage, volumetric/deviatoric coupling, temperature, and aging. The objective
will be accomplished by applying the elastic-viscoelastic correspondence principle
and the continuum damage theory. The constitutive model will be incorporated
into the ABAQUS finite element code and used to predict the response and performance
of laboratory pavements loaded by the Model Mobile Load Simulator. Nondestructive
surface wave tests will be performed to determine the change in material properties
due to fatigue damage growth.
Development of Specification Testing to Promote Fracture Fatigue Resistance
and to Optimize Microdamage Healing
Y. R. Kim and M. N. Guddati
Texas A&M Research Foundation/Western Research Institute/Federal Highway
Administration
7/99 to 6/03
The ultimate goal of this project is “to be able to classify/specify/improve
asphalts by their healing rates and efficiencies using chemical data that can
be acquired more rapidly than by mechanical methods.” To accomplish this
goal, the viscoelastic, continuum damage model developed by the PI will be tied
to the micromechanical properties of component materials using microscopic lattice
modeling. Various test methods will be explored for binder specification
testing using the viscoelastic, continuum damage formulation and micromechanical
simulation with an objective to promote fatigue resistance and to optimize the
microdamage healing potential.
Analysis of an Instrumented Jointless Bridge
M. J. Kowalsky
NC Department of Transportation (NCDOT)
8/00 to 7/02
Through the use of remote data acquisition, the behavior of an instrumented
jointless bridge is explored. The bridge structure, located in Haywood
County, North Carolina, was recently rehabilitated by NCDOT. As part of
the rehabilitation, the superstructure was widened and a jointless link-slab
deck employed. The goals of the research are to validate analysis and
design assumptions, investigate limit-states design methods, and develop a strategy
and guide for long-term monitoring of jointless link-slab bridges.
Limit-States Seismic Design for Concrete Bridges and Buildings
M. J. Kowalsky
1998, ongoing
The objective of the research is to develop comprehensive methods for achieving
limit-states design for structural systems with a specific emphasis on concrete
structures. This requires characterization of limit states at various
levels of performance as well as development of rational deformation-based seismic
design procedures.
Pilot Studies in Performance-Based Engineering of Clay Masonry Walls and Reinforced
Concrete Columns Under Extreme Natural Hazard Conditions
M. J. Kowalsky
Faculty Research and Professional Development Grant
1/00 to 6/01
It is the objective of this research to investigate the behavior and characterize
the performance of confined clay masonry walls and reinforced concrete bridge
piers under severe lateral force conditions. Methods of confining clay
masonry walls are explored with the primary objective of enhancement of strain
capacity. A tension strain-based model for buckling of reinforcement in
RC bridge piers is explored through reversed cyclic testing and analytical studies.
Precast Post-Tensioned Clay Masonry Walls for High Performance Modular Housing
M. J. Kowalsky
National Science Foundation
8/00 to 7/02
This research is geared towards development of a housing construction technique
that utilizes pre-cast masonry elements to achieve modular housing. A
significant portion of the research is dedicated towards understanding the behavior
of the primary load bearing elements in this system: pre-cast, post-tensioned
clay masonry walls. Through the use of reversed cyclic testing, shake
table testing, and analytical studies, the effect of confinement, grouting,
and bonding on pre-cast post-tensioned walls is explored. The research
aims to reduce the risk of life, injury, and property destruction from natural
hazards while improving durability and reducing maintenance costs of affordable
modular housing.
Seismic Assessment of Bridges in Areas of Moderate Seismicity
M. J. Kowalsky
1998, ongoing
Bridges in regions of moderate seismic activity present several assessment problems.
Typically, such structures contain details that are highly deficient in terms
of shear strength and ductility capacity. The objective of this research
is to develop simple deformation-based assessment procedures that can be used
by engineers for bridges in moderate seismic regions. The proposed techniques
will be compared with more complex methods such as dynamic inelastic time history
analysis.
Strain Limit States and Behavior of Clay Masonry Under Lateral Load Conditions
M. J. Kowalsky
1998, ongoing
North Carolina produces over 15% of the clay masonry for the entire nation.
The primary use of this material is for building facade elements; however, no
conceptual difficulty exists that prevents its use for load bearing walls subjected
to high lateral forces. This ongoing research project has the objective
of characterizing the performance of clay masonry, both brick and block, under
lateral load conditions. This includes reinforced as well as pre-stressed
masonry. Of particular interest is characterization of strain, strength,
and energy dissipation capacity for confined, unconfined, fully grouted, and
partially grouted systems.
High-Performance Composite Infrastructural Systems Utilizing Advanced Cementitious
Composites
N. Krstulovic-Opara, S. Ahmad, and P. Zia
National Science Foundation - Earthquake Hazard Mitigation, US-Japan Cooperative
Research Program
9/96 to 8/01
The goal of this project is to provide novel solutions to the problem of rapidly
deteriorating civil infrastructure. This is achieved by selectively using
high-performance composite materials, including: (1) Slurry Infiltrated Mat
Concrete (SIMCON), (2) Slurry Infiltrated Fiber Concrete (SIFCON), and (3) High
Strength - Lightweight Aggregate Fiber Reinforced Concrete, to develop cost-effective,
partially-cast-in-place High-Performance Composite Frame Systems (HPCFSs).
Such HPCFSs will exhibit substantially higher strength, seismic resistance,
ductility, and durability. The project consists of both an analytical
and an experimental component. Behavior at 2/3-scaled HPCF beam, column,
and "fuse" members is evaluated under static-reversed cyclic loading.
It is anticipated that, if successful, this project will open a new approach
in developing durable and cost-effective infrastructural systems, important
for the economical well-being of the United States in the next century.
Multiaxial Modeling and Optimization of High-Performance Fibrous Composites
N. Krstulovic-Opara
National Science Foundation - Office of International Programs and Earthquake
Hazard Mitigation, US-Japan Cooperative Research Program and Division of International
Programs
9/97 to 8/01
The main goal of the proposed project is to evaluate, optimize and model multiaxial
behavior of Slurry Infiltrated Mat Concrete (SIMCON). The research is
conducted through the international exchange with the Institute of Fundamental
Technological Research, Polish Academy of Sciences. The specific objectives
are (1) optimizing micromechanical properties of SIMCON, (2) experimentally
establishing relationships between micromechanical parameters and macromechanical
properties, and (3) developing a multiaxial finite element model for SIMCON.
B Stress Index: Monotonic and Cyclic Loading
V. C. Matzen and T. Hassan
Center for Nuclear Power Plant Structures, Equipment and Piping,
1/01 to 12/01
Conduct experiments on piping elbows by subjecting them to cyclic loading, both
in-plane and out-of-plane. Verify that nonlinear FEA can accurately simulate
the experimental results. Using FEA, determine failure loads for a variety
of elbow sizes and schedules. Propose a new definition for B2 for cyclic
loading.
Experimental Investigation of Sliding and Rocking
V. C. Matzen
Center for Nuclear Power Plant Structures, Equipment and Piping
1/00 to 12/00
Conduct shake table experiments on unanchored objects to verify analytical model
of sliding behavior. Determine sensitivity of response to input motion
parameters and to support characteristics such as smoothness and geometry.
Concluded that both static and kinetic coefficients of friction were needed
for accurate simulation.
Determination of the Modulus of Elasticity of Concrete from Dynamic Tests
J. Nau and M. L. Leming
1998, ongoing
The objective of this project is to evaluate the modulus of elasticity of concrete
from dynamic tests on thick cylindrical samples. This study formed the basis
of the independent study project for one MCE student. One journal article
has been published. Work continues to relate the modulus of elasticity
and other dynamic properties including damping to permeability and other measures
of deterioration.
Evaluation of the Equivalent Lateral Force Procedure for Seismic Design of
Irregular Buildings
J. Nau
1998, ongoing
The objective of this research is to examine the limitations of the equivalent
lateral force procedure for the seismic design of buildings with structural
discontinuities. This study formed the basis of the thesis for one M.S.
student. One journal article was published in January 1997; one Ph.D.
student completed his degree in 2000. A paper based upon his doctoral
dissertation is currently under review.
Performance of Coped and Uncoped Framed Beam Connections
J. Nau and D. W. Johnston
6/99 to 6/01
The possibility of using extended clip angles in framed steel beam connections
is investigated experimentally and the results analyzed. Use of extended
clip angles reduces the cost of coping beam flanges. However, the performance
of extended double and single angle connections in comparison to conventional
coped framed beam connections with shorter angle legs has not been previously
investigated. The test fixture and 48 specimens were fabricated and donated
by Steel-Fab, a structural steel fabricator in Charlotte, NC.
Experimental Testing of DuraSpanTM Fiber-Reinforced Polymer (FRP) Bridge Deck
S. H. Rizkalla and A. Z. Fam
Martin Marietta Composites
9/00
Reinforced concrete bridge decks suffer from rapid deterioration, especially
in the northeast of the United States and Canada, due to severe temperature
effects and use of salt for deicing the roads, which result in an accelerated
corrosion process of the steel reinforcement. A new Glass-FRP bridge deck
is introduced to overcome the serious durability issues. This project
provides structural testing of the new deck using AASHTO specifications to simulate
truck loads. The two profiles considered are the 7.66-in.-thick and the
5-in.-thick decks.
Repair of Aluminum Truss Joints Using Fiber Reinforced Polymers (FRP)
S. H. Rizkalla and A. Z. Fam
Fyfe Co. LLC
4/01
An innovative technique is introduced to repair the joints of aluminum
trusses using FRP. In this project, damage of the welded joint is
simulated by grinding the weld before applying a number of FRP layers to
the joint in both the longitudinal and circumferential directions of the
members. The diagonal members are tested in tension to evaluate the
strength of the repaired joint.
Moisture Effect on Durability of Axially Loaded Concrete-Filled Tubular FRP Piles
S. H. Rizkalla, J. Lesko (Virginia Tech), and A. Z. Fam
Joint Project, NC State University and Virginia Tech.
5/01
Concrete-filled glass-FRP tubes are investigated as a possible foundation
alternative for projects located in harsh marine environments. Research
at Virginia Tech has found that moisture is the dominant damage mechanism,
which influences the long-term durability and strength of concrete-filled
FRP piles. Two brands of commercially available concrete-filled FRP
tubes are considered.
Concrete-Filled Fiber Reinforced Polymer Rectangular Tubes
S. H. Rizkalla and A. Z. Fam
NC State University, ISIS Canada
1/01
FRP box sections filled with concrete have the advantage of utilizing
the FRP tube as permanent formwork and as reinforcement at the same time.
The filament-wound FRP tube includes fibers oriented in both the longitudinal
and transverse directions for flexural and shear strength. Both beams
and columns are tested.
The Implementation of High Performance Concrete in a Set of Dual (North and
South Bound) Four-Span Bridges to be Constructed on US 401 Over Neuse River
in Wake County, NC
P. Zia and M. J. Kowalsky
NC Department of Transportation
10/96 to 6/01
High performance concrete (HPC) with higher compressive strength (in the range
of 8,000 to 10,000 psi) and increased durability is rapidly gaining acceptance
for bridge construction. The goal of this project is to implement and
demonstrate the economic benefits of the HPC technology in bridge design and
construction in North Carolina, thereby providing a greater value to the public.
Specifically, the project will monitor the production of HPC in typical plant
and field conditions, confirm the feasibility of producing HPC bridge girders
and decks, and validate the expected behavior of bridge superstructures built
with HPC girders and decks.
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