1. Postdoctoral Fellow, Dept. of Civil, Geological and Mining Engineering, École Polytechnique, Montréal H3T 1J4, Canada.
2. Professor, Dept. of Civil Engineering, Univ. of Toronto, 35 St. George St., Toronto ON, Canada M5S 1A4 (corresponding author).
3. Associate Professor, Dept. of Civil Engineering, Univ. of Toronto, 35 St. George St., Toronto ON, Canada M5S 1A4.