1. Professor, Dept. of Civil Engineering, Seoul National Univ., San 56-1, Shinrim-dong, Gwanak-gu, Seoul, Korea.
2. Senior Researcher, Research Institute of Engineering Science, Seoul National Univ., San 56-1, Shinrim-dong, Gwanak-gu, Seoul, Korea.
3. Research Assistant, Dept. of Civil Engineering, Seoul National Univ., San 56-1, Shinrim-dong, Gwanak-gu, Seoul, Korea.