1. Assistant Professor, Dept. of Civil Engineering, Univ. of Toronto, 35 St. George St., Toronto, Canada M5S 1A4 (corresponding author).
2. Research Assistant, Univ. of Toronto, 100 St. George St., Toronto, Canada M5S 3G3.
3. Bahen Tanenbaum Professor, Dept. of Civil Engineering, Univ. of Toronto, 35 St. George St., Toronto, Canada M5S 1A4.