1. PhD, Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Daejeon 305-701, Korea (corresponding author).
2. PhD, KORDI, Yuseong P.O. Box 23, Daejeon 305-343, Korea.
3. Professor, Dept. of Civil and Environmental Engineering, Sejong Univ., 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, Korea.
4. Professor, Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Daejeon 305-701, Korea.