1. Graduate Research Assistant, Dept. of Civil and Environmental Engineering, Sejong Univ., 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, KR, e-mail: manh_tuan@hotmail.com
2. Ph.D., Professor, Dept. of Civil and Environmental Engineering, Sejong Univ., 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, KR (Corresponding author), e-mail: hlee@sejong.ac.kr
3. Ph.D., Research Professor, Dept. of Civil and Environmental Engineering, Sejong Univ., 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, KR, e-mail: jongeunbaek@sejong.ac.kr