1. Research Associate, Dept. of Civil Engineering, Tohoku Univ., 06 Aza Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan.
2. Professor, Dept. of Civil Engineering, Tohoku Univ., 06 Aza Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan.
3. Lecturer, Dept. of Civil Engineering, Tohoku Univ., 06 Aza Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan.
4. Graduate Student, Dept. of Civil Engineering, Tohoku Univ., 06 Aza Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan.