1. Postdoctoral Fellow, Dept. of Civil and Environmental Engineering, Univ. of Waterloo, Waterloo, ON, Canada, N2L 3G1; presently, on leave from Dept. of Civil Engineering, Cairo Univ., Egypt.
2. Professor and Canada Research Chair, Dept. of Civil and Environmental Engineering, Univ. of Waterloo, Waterloo, ON, Canada, N2L 3G1 (corresponding author).
3. Distinguished Professor Emeritus, Dept. of Civil and Environmental Engineering, Univ. of Waterloo, Waterloo, ON, Canada, N2L 3G1.