1. Research Assistant, Dept. of Civil and Environmental Engineering, Chung-Ang Univ., 84 Heukseok-ro, Dongjak-gu, Seoul 156-756, Republic of Korea.
2. Assistant Professor, College of Transport and Communications, Shanghai Maritime Univ., 1550 Haigang Ave., Shanghai 201306, China.
3. Professor, Dept. of Civil and Environmental Engineering, Chung-Ang Univ., 84 Heukseok-ro, Dongjak-gu, Seoul 156-756, Republic of Korea (corresponding author).