Civil Engineering CE
5990 Graduate Seminar
Three graduate students will present their research topics in our Civil
Engineering Seminar. This Thursday- 4-5PM 11/10/2011, Dow 642:
Presentation 1:
The Incorporation of Discontinuous Fibers into the Structural Design of
Cementitious Materials: A Look at UHPC
by Eric L. Kreiger
Civil/Structural Engineering Master's Student
Abstract
The use of fibers in cementitious materials has existed for several
decades. However, their incorporation into structural design has been
limited. In normal strength concrete their primary purpose is crack
control, which leads to improved post cracking behavior. The fibers are
considered secondary tensile reinforcement, overshadowed by the primary
reinforcing bars. With the introduction of Ultra High Performance
Concrete (UHPC) the fibers play a much bigger role in the tensile
capacity of structural members. This presentation will briefly cover the
reason for this and how the use of fibers affects structural design. As
well as, the models that currently exist to describe the post cracking
behavior and the research being conducted to model the fracture of UHPC.
Presentation 2:
Probabilistic Analysis via Aeroelasticity and System Identification on
Wind Turbine Blades for Operational Structural Integrity Assessment
by Antonio Velazquez, Ph.D Student
Abstract:
Wind energy is an increasingly important component of this
nation’s renewable energy portfolio. Safe operation of wind
turbine structures requires not only information regarding
their condition, but their operational environment. Given
the difficulty inherent in SHM processes and the stochastic
nature of wind loads, a probabilistic framework is appropriate
to characterize their risk of failure at a given time.
Such information will be invaluable to turbine controllers,
allowing them to operate the structures within acceptable
risk profiles. A modified along-wind aeroelastic analysis
adopting rotationally-sampled wind-field spectral functions is studied
in combination with modal subspace identification tecnhiques, such
as Eigensystem Realization Algorithm (ERA) and Partial Observer
Markovs (POM). The study further explores characterization of the
turbine loading and response envelopes for critical failure
modes of the turbine blade structures.
Presentation 3:
Bond Strength between UHPC and Normal Strength Concrete (NSC) in
accordance with Split Prism and Freeze-Thaw cycling tests
by Miguel Angel Carbonell
CEE Graduate Student
Abstract:
The rehabilitation of concrete structures, particularly within
transportation infrastructure network is a major challenge for
transportation agencies in the United States. This is especially true
for concrete bridge decks, which are often subjected to severe operating
conditions, both environmental and man-made. Often, the most appropriate
strategy to preserve or rehabilitate these structures is to provide some
form of a protective coating or barrier. These surface treatments have
typically been some form of polymer, asphalt, or low-permeability
concrete, but the application of UHPC (Ultra High Performance Concrete)
has shown promise for this application mainly due to its negligible
permeability, but also as a result of its excellent mechanical
properties, self consolidating nature, rapid gain strength and minimal
creep and shrinkage characteristics. However, for widespread acceptance,
durability and performance of the composite system must be fully
understood, specifically the bond between UHPC deck and normal concrete
typical for bridge decks. It is essential that the bond offers enough
strength in order to resist the stress due to mechanical loading or
thermal effects while also maintaining an extended service-life performance.
An experimental study was performed to assess the bond performance of
UHPC for overlay applications. Pre-wetting conditions, surface
preparation, freeze-thaw cycling and indirect tensile strength were
variables taken into account to study such performance. A total of 60
composite and 7 monolithic concrete specimens, 102x76x394 mm, were cast
to test in indirect tension. Experimental results showed that samples
subject to 300 freeze-thaw cycles present greater bond strength than
samples of the same age without freeze-thaw cycles, and all samples in
which the moisture condition of the substrate is saturated before
placing UHPC achieves excellent bond strength which amply satisfies the
range specified in the ACI Concrete Repair Guide.
Public welcome.
Our seminar is archived: http://www.cee.mtu.edu/grad/CE_seminar/index.html
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