1. Assoc. Prof. of Civ. Engrg., Dept. of Civ. Engrg. and Engrg. Mechanics, Columbia Univ., New York, N. Y.
2. Research Assoc., Dept. of Civ. Engrg. and Engrg. Mechanics, Columbia Univ., New York, N. Y.; on leave from Railway Technical Research Inst., Japan National Railway, Tokyo, Japan.