1. Ph.D. Candidate, Dept. of Civil Engineering, Amirkabir Univ. of Technology, #424 Hafez Ave., P.O. Box 15875-4413, Tehran, Iran.
2. Professor, Dept. of Civil Engineering, Amirkabir Univ. of Technology, #424 Hafez Ave., P.O. Box 15875-4413, Tehran, Iran (corresponding author).