1. Research Associate, Dept. of Civil Engineering, Sharif Univ. of Technology, P.O. Box 11365-8639, Tehran, Iran.
2. Professor, Dept. of Civil Engineering, Sharif Univ. of Technology, P.O. Box 11365-8639, Tehran, Iran.
3. Professor, Division of Civil Engineering, School of Engineering, Physics and Mathematics, Univ. of Dundee, Dundee DD1 4HN, Scotland, U.K. (corresponding author).