1. Assistant Professor, Dept. of Civil Engineering, Univ. of British Columbia, CEME-2004C, 6250 Applied Science Ln., Vancouver, BC, Canada V6T 1Z4 (corresponding author).
2. Research Scientist, Dept. of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave. Bldg. E19-625, Cambridge, MA 02139.
3. Principal Research Scientist, Materials Research Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Ave. Bldg. E19-625, Cambridge, MA 02139.