1. PhD Candidate, Dept. of Civil Engineering, Colorado State Univ., Fort Collins, CO 80523-1372; formerly, Graduate Student, School of Civil, Urban and Geosystem Engineering, College of Engineering, Seoul National Univ., Gwanak-Ku 151-742, Seoul, Korea.
2. Assistant Professor, School of Civil, Urban and Geosystem Engineering, College of Engineering, Seoul National Univ., Gwanak-Gu 151-742, Seoul, Korea.
3. Associate Professor, School of Civil, Urban and Geosystem Engineering, College of Engineering, Seoul National Univ., Gwanak-Ku 151-742, Seoul, Korea (corresponding author). E-mail: jaeykim@snu.ac.kr