1. Ph.D. Student, School of Electrical and Computer Engineering, Robotics Institute, Georgia Institute of Technology, 777 Atlanta Dr. N.W., Atlanta, GA 30332-0355.
2. Ph.D. Candidate, School of Civil and Environmental Engineering, Georgia Institute of Technology, 790 Atlanta Dr., Atlanta, GA 30332-0355.
3. Associate Professor, School of Civil and Environmental Engineering, Georgia Institute of Technology, 790 Atlanta Dr. N.W., Atlanta, GA 30332-0355 (corresponding author).
4. Professor, Dept. of Architectural Engineering, Chung-Ang Univ., 221 Heuksuk-dong, Dongjak-gu, Seoul 156-756, Korea.