1. Prof., Dept. of Engrg. Sci. and Mech., Virginia Polytechnic Inst. and State Univ., Blacksburg, VA 24061. E-mail: librescu@vt.edu
2. Sr. Consultant, Dept. of Civ. and Struct. Engrg., Halliburton, Brown & Root Energy Services, 10200 Bellaire Blvd., Houston, TX 77072-5299.