1. Assoc. Prof., Dept. of Civ. Engrg., Korea Advanced Inst. of Sci. and Technol., 373-1 Kusong-dong, Yusong-gu, Taejon 305-701, Korea.
2. Grad. Student, Dept. of Civ. Engrg., Korea Advanced Inst. of Sci. and Technol., 373-1 Kusong-dong, Yusong-gu, Taejon 305-701, Korea.