Principal Investigator(s) and
Institution(s)
John Mander, University at Buffalo
Objective
Following a strong earthquake, perhaps the most important question facing a bridge owner
is whether or not a particular bridge has been damaged and to what extent. If there are
visible signs of damage, is the bridge safe enough to allow continued traffic on it?
Answering this question is relatively easy for an experienced engineer when assessing a
damaged bridge that has not been retrofitted, as the damage is generally self-evident.
However, if a bridge has been retrofitted with either cable-restrainers, column jackets,
foundation improvements, or a combination thereof, the damage may not be visible or easy
to assess. In this case, the engineer may need to resort to nondestructive evaluation
(NDE) techniques as a means of damage detection and to assess the severity of damage.
Although there are many different nondestructive evaluation (NDE) methods, those that are
appropriate for rapid post-earthquake evaluation of bridges have not been specifically
identified nor have they been, for the most part, validated against retrofitted bridge
components. The objective of this task is to conduct a review and assessment of NDE
methodologies that could be used for assessing damage in reinforced concrete columns that
have been retrofitted using steel or composite jackets.
Approach
Concerns have been raised as to the ability of bridge columns that have been
seismically-retrofitted using steel or composite jackets to continue to perform adequately
after an earthquake. Jackets confine the column core concrete and, if properly designed
and constructed, should relocate damage elsewhere in the structure - either in the
connection, the gap between the jacket and the joint, or the longitudinal reinforcing
steel. As a result of low cycle fatigue effects, the longitudinal rebar may be plastically
strained to the extent that they may be close to fracture. The concern is further
complicated if the jacket is a composite material that can deteriorate through aging. As a
result, methodologies need to be investigated and developed which can determine if a
retrofitted bridge column has been damaged during an earthquake and, if so, to what
extent. In addition, the technology should enable remaining life or capacity assessments
of jacketed columns. This task will review and assess the capabilities of various NDE
techniques along with other possible inference methods for these purposes.
NDE Survey - A state-of-practice survey will be made of contemporary NDE methodologies to
critically evaluate and ascertain the viability of various approaches for this
application. It is envisaged that a number of technologies will be considered including
acoustic emission, radar, ultrasonic methods, radiography, and microscopy. It is known
that Caltrans has sponsored limited studies in this regard with the Aerospace Corporation
and Lawrence Livermore National Laboratories. Information from these and other studies
will be gathered and assessed. In addition, vendors of NDE technologies will be approached
and asked to provide other research and application results. The merits of classical
visual and manual NDE methods will also be evaluated, specifically for those situations
where damage has been forced to occur in visually-inspectable areas (e.g., in the gaps at
the top and bottom of the column jacket).
Computational Inference - Earthquake damage to bridge columns results, in some cases, from
low cycle fatigue effects. Therefore, a companion assessment strategy based on a
computational methodology to predict the remaining life of earthquake-damaged jacketed
columns will be developed. This approach will use ground motions records to assess
previous earthquake-induced inelastic displacement history and, hence, damage to pier
columns. On this basis, the remaining life of the columns can be inferred. This work will
draw heavily on previous energy-based theoretical developments made by Mander, Chang, and
Dutta, under FHWA/MCEER Project DTFH61-92-C-00106.
If feasible, one or more of these technologies will be assessed in Year 1 by applying it
to a fabricated component representative of a steel or composite jacketed column in
limited laboratory testing. Technologies and methods which show promise in their potential
application to jacketed columns will then be selected for further research in Year 2. It
is anticipated that a series of laboratory and field evaluations will be conducted and,
based on their results, improvements or modifications will be suggested for those that
show promise.
Anticipated Start Date and Duration
January 1, 1999 - 12 months
9/24/99 |