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. Senior Civil Engineer, Hyundai Industrial Development Co. Ltd., Samsung-dong, Kangnam-gu, Seoul, Korea.
3. Research Associate, Dept. of Civil Engineering, Seoul National Univ., San 56-1, Shinrim-dong, Gwanak-gu, Seoul 151-742, Korea. E-mail: zerofel@snu.ac.kr