1. Members, ASCE
2. Prof., Dept. of Civ. Engrg., Nat. Univ. of Mexico, Apartado Postal 70-165, Mexico City 04510, Mexico. E-mail: jadrdiaz@servidor. unam.mx
3. Prof., Dept. of Civ. and Envir. Engrg., Georgia Inst. of Technol., Atlanta, GA 30332. E-mail: carlos@ce.gatech.edu