1. Prof. of Civ. Engrg., Univ. of São Paulo, BR-13560970 São Carlos, Brazil. E-mail: tbcelest@usp.br
2. Asst. Prof. of Engrg. Mech., Univ. of Nebraska, Lincoln, NE 68588. E-mail: rpiltner@unlserve.unl.edu
3. Prof. of Civ. Engrg., Univ. of California, Berkeley, CA 94720. E-mail: monteiro@ce.berkeley.edu
4. Assoc. Prof. of Civ. Engrg., Univ. of California, Berkeley, CA 94720. E-mail: ostertag@ce.berkeley.edu