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Current and Past Research Activities
Followings are selected list of current and past research activities that I have been involved . List of relevant publications are available in the Publications link.
Seismic Displacement Demands on Skewed Bridge Decks Supported on Elastomeric Bearings
After 2010 Chile Earthquake, it was observed that several skew bridges suffered damage due to displacment or unseating of brigdge decks.
One of the bridges shown in the picture displaced by 1.5m in transverse direction and one of the three girders were unseated. After the field investigation,
numerical study was carried out to understand how the skew angle influence the displacement demands on bridge superstructure. Preliminary
results show that the skew angle does not largely increase the displacement demand in skew direction, but have large effects on the displacement demand in normal-to-abutment direction.
In addition, I realized that it is quite difficult to get 1.5m of lateral displacement withthe anlytical model even with a very large intensity motion. There is a clear limitation
on our understanding of the seismic response of bridge elements (bridge bearings; SSI between aubtments, embankments, and bridge deck; numerical model) and further experimental
and analytical studies are necessary.
Animation of seismic response of one-span bridge is uploaded on YouTube and can be accessed through the following link.
Calibration of LRFD Factors for Bridge and Foundation Design
The objective of this project was to calibrate load and resistance factors in LRFD Design Guidelines for bridges. The bridge inventory in Missouri was analyzed to systematically select most representative bridges. With past five years of weigh-in-motion (WIM) data, the selected bridges were analyzed and reliability index were estimated. The ultimate objective of this project was to calibrate load and resistance factors considering actual bridge design and construction practice and truck load in Missouri. The project was funded by Missouri Department of Transportation.
UI-SimCor: A Framework for Distributed Analytical and Hybrid Simulations
SimCor is a framework for hybrid simulation which allows substructure pseudo-dynamic simulation of buildings and bridges.
It was developed for NEES community and has been used in several research projects in the U.S. and abroad.
For pseudo-dynamic simulation using SimCor, the mass and Rayleigh damping are modeled in SimCor while nonlinear restoring
forces are represented by structural analysis application or experimental specimen. At each step of time integration, SimCor
predicts displacement or velocity at next time step and the predicted values are sent to analysis application or controller for
experiment. Then the application or experiment are conducted and measured forces are returned back to SimCor. Based on the
measured response, the predicted values are corrected. In the current version of SimCor, Alpha-Operator Splitting Integration
scheme is implemented.
The latest version is available on NEEShub. UI-SimCor
Seismic Performance Evaluation of Buildings and Bridges
I led several research tasks related to seismic performance evaluation of buildings and bridges including three-story OMRCF building's seismic fragility derivation, seismic performance evaluation of 59-span bridge crossing Mississippi River, seismic fragility evaluation of a bridge in Central and Eastern U.S.
Soil Structure Interaction Analysis
To account for soil-structure interaction in the event of an earthquake, soil and foundation domain are modeled with three-dimensional soil material model which can represent behavior of cohesive and cohesionless soils and liquefaction effects.
For the seismic performance evaluation of bridges in the above, soil and foundation are modeled in OpenSees while structure is modeled in Zeus-NL. Both are integrated with SimCor. The effect of SSI on seismic fragility of bridges is significant. In fact, due to large uncertainties and different assumptions in various modeling approach, such as lumped spring model, pile-on Winkler-type spring model, three-dimensional continuum model, the seismic fragility curve varies a lot depending on which method is adopted. The SSI has been a research topic for a long time but the analysis methods are still continuously evolving to understand the SSI effect with more realistic models and methods.
Field Missions
I participated in field missions after Hurricane Katrina in 2005, Piso-Chincha Earthquake, Peru in 2007, and Chile Earthquake in 2010. The field mission to the coast of Louisiana and Mississippi afTer Hurricane Katrina was to investigate effects of hurricane to transportation system including roads and bridges. The missions after two earthquakes were to understand failure modes of structures, collect field data, and carry out post-earthquake analysis of damaged structures. The reports for the field missions are published and listed in Publications link.