1. Assistant Professor, Dept. of Civil Engineering, Univ. of British Columbia, Civil and Mechanical Engineering Bldg., 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.