1. Faculty of Engrg., Univ. of Tehran, Tehran, Iran
2. Prof. of Civ. Engrg., and Applied Mathematics, Tech. Inst., Northwestern Univ., Evanston, Ill. 60201
3. Prof. of Civ. and Mech. Engrg., Tech. Inst., Northwestern Univ., Evanston, Ill. 60201
4. Research Assoc., Civ. Engrg., Univ. of Utah, Salt Lake City, Utah 84112