1. Ph.D. Student, Dept. of Civil Engineering, Univ. of Waterloo, Waterloo, ON, Canada N2L 3G1; and Lecturer (on leave), Dept. of Civil Engineering, Univ. of Engineering and Technology Lahore, Pakistan.
2. Professor and Canada Research Chair, Dept. of Civil Engineering, Univ. of Waterloo, Waterloo, ON, Canada N2L 3G1 (corresponding author).