1. Professor, Dept. of Civil Engineering, Seoul National Univ., San 56-1, Shinrim-dong, Gwanak-gu, Seoul 151-742, Korea (corresponding author). E-mail: bhohcon@snu.ac.kr
2. Manager, Civil Engineering Team, SK Engineering and Construction, 192-18 Kwanhun-dong, Jongro-gu, Seoul, Korea.
3. Research Associate, Dept. of Civil Engineering, Seoul National Univ., San 56-1, Shinrim-dong, Gwanak-gu, Seoul 151-742, Korea.