Principal Investigator and Institution
M. Shinozuka, University of California, Irvine
Objective
In Research Year 2, the effect of bridge seismic retrofitting by means
of steel column jacketing on fragility curves of bridges and highway
networks was assessed via Task B13. This was done under the assumption
that the totality of the bridges under consideration form a statistically
homogeneous population. In Research Year 3, this assumption will be
removed, and the population of bridges will be divided into a number of
bridge classes with each class possessing a similar set of structural and
other characteristics. Bridges will be categorized depending on whether
they are comprised of single or multiple spans; they are built on soft,
medium, or hard soils; and whether their skew is light, moderate, or
severe. This will result in a combination of 18 bridge classes.
Approach
Fragility curves for retrofitted bridges will be estimated by making
use of the correlation that exists between fragility parameters (e.g.,
medians and logstandard deviations) and hysteretic parameters (e.g.,
yield point; or first and second elastic moduli in a bilinear
momentcurvature (or rotation) curves of the columns). This task will
establish the correlation and develop the fragility curves of the bridges
retrofitted on the basis of the corresponding curves associated with
bridges not retrofitted for each bridge class. Then, using all these
fragility curves, a network analysis will be conducted to evaluate the
effect of retrofit by computing increased amount of drivers' delay as the
measure of degree of deterioration of the network subjected to a specific
OD characteristics of the region.
For the 18 bridge classes to be considered, empirical fragility curves
will be developed based on the Northridge earthquake damage data for
bridges which were not retrofitted with steel or other column jackets.
Fragility curves for the bridges retrofitted by steel jackets will then be
obtained by the correlational analysis method developed in Task B13
during Research Year 2. These two sets of fragility curves (bridges both
unretrofitted and retrofitted) will be used in the network analysis to
evaluate the performance of highway networks (e.g., in the Los Angeles
area) and to identify the difference in the performance when the bridges
are assumed to constitute a homogeneous sample and when they are
classified into nonhomogeneous classes. It is quite possible that the
nonhonogeneous population, which is much more realistic, can predict a
significantly lesser degree of performance.
Products
A technical report describing the analytical procedures used to develop
the fragility curves for each bridge class, the analysis of network
performance, and the estimation of retrofit impacts on network
performance. The retrofitted bridge fragility curves can then be
implemented in future versions of REDARS.
Technical Challenges
The correlation between fragility and hysteretic parameters may be
rather fuzzy.
