1. Professor, Dept. of Civil Engineering, Seoul National Univ., San 56-1, Shinrim-dong, Kwanak-gu, Seoul, Korea.
2. Research Associate, Dept. of Civil Engineering, Seoul National Univ., San 56-1, Shinrim-dong, Kwanak-gu, Seoul, Korea.
3. Graduate Research Assistant, Dept. of Civil Engineering, Seoul National Univ., San 56-1, Shinrim-dong, Kwanak-gu, Seoul, Korea.