| dc.description.abstract | Bridges play a key role in the transportation sector while serving as lifelines for the economy and
safety of communities. The need for resilient bridges is especially important following natural
disasters, where they serve as evacuation, aid, and supply routes to an affected area. Much of the
earthquake engineering community is interested in improving the resiliency of bridges, and many
contributions to the field have been made in the past decades, where a shift towards performancebased design (PBD) practices is underway. While the Canadian Highway Bridge Design Code
(CHBDC) has implemented PBD as a requirement for the seismic design of lifeline and major
route bridges, the nature of PBD techniques translate to a design process that is not universally
compatible for all scenarios and hazards. Therefore, there is great benefit to be realised in the
development of PBD guidelines for mainshock-aftershock seismic sequences for scenarios in
which the chance to assess and repair a bridge is not possible following a recent mainshock. This
research analytically explored a parameterized set of 20 reinforced concrete bridge piers which
share several geometrical and material properties with typical bridge bents that support many
Canadian bridges. Of those piers, half are designed using current PBD guidelines provided in the
2019 edition of the CHBDC, whereas the remaining half are designed with insufficient transverse
reinforcement commonly found in the bridges designed pre-2000. To support this study, a
nonlinear fiber-based modelling approach with a proposed material strength degradation scheme
is developed using the OpenSEES finite element analysis software. A multiple conditional mean
spectra (CMS) approach is used to select a suite of 50 mainshock-aftershock ground motion
records for the selected site in Vancouver, British Columbia, which consist of crustal, inslab, and
interface earthquakes that commonly occur in areas near the Cascadia Subduction zone. Nonlinear
time history analysis is performed for mainshock-only and mainshock-aftershock excitations, and
static pushover analysis is also performed in lateral and axial directions for the intact columns, as
well as in their respective post-MS and post-AS damaged states. Using the resulting data, a
framework for post-earthquake seismic capacity estimation of the bridge piers is developed using
machine learning regression methods, where several candidate models are tuned using an
exhaustive grid search algorithm approach and k-fold crossvalidation. The tuned models are fitted
and evaluated against a test set of data to determine a single best performing model using a multiple
scorer performance index as the metric. The resulting performance index suggests that the decision
tree model is the most suitable regressor for capacity estimation due to this model exhibiting the
highest accuracy as well as lowest residual error. Moreover, this study also assessed the fragility
of the bridge piers subjected to mainshock-only and mainshock-aftershock earthquakes.
Probabilistic seismic demand models (PSDMs) are derived for the columns designed using current
PBD guidelines (PBD-compliant) to evaluate whether the current PBD criteria is sufficient for
resisting aftershock effects. Additional PSDMs are generated for the columns with inadequate
transverse reinforcement (PBD-deficient) to assess aftershock vulnerability of older bridges. The
developed fragility curves indicate an increased fragility of all bridge piers for all damage levels.
The findings indicate that adequate aftershock performance is achieved for bridge piers designed
to current (2019) CHBDC extensive damage level criteria. Furthermore, it is suggested that
minimal damage performance criteria need to be developed for aftershock effects, and the
repairable damage level be reintroduced for major route bridges. | en_US |
