Christian Hellmich Univ. Asst., Inst. for Strength of Mat., Univ. of Technol. of Vienna, Karlsplatz 13/202, A-1040 Vienna, Austria. E-mail: christian.hellmich@ tuwien.ac.atAssoc. Prof., Massachusetts Inst. of Technol., Dept. of Civ. and Envir. Engrg., 77 Massachusetts Ave., Cambridge, MA 02139-4307; formerly, Laboratoire Central des Ponts et Chaussées, Paris, France. E-mail:
[email protected]., Inst. for Strength of Mat., Univ. of Technol. of Vienna, Karlsplatz 13/202, A-1040 Vienna, Austria. E-mail:
[email protected]