1. Res. Sci., Commonwealth Scientific and Industrial Res. Org. Div. of Build., Constr. and Engrg., P.O. Box 56, Highett, Victoria 3190, Australia. E-mail: chi-hsiang.wang@dbce.csiro.au
2. Prof., Dept. of Civ. and Envir. Engrg., Univ. of Illinois at Urbana-Champaign, 3129-e NCEL, 205 N. Mathews Ave., Urbana, IL 61801. E-mail: y-wen@uiuc.edu