1. Assistant Professor, School of Civil Engineering, College of Engineering, Univ. of Tehran, 16 Azar Ave., P.O. Box 11155-4563, Tehran, Iran (corresponding author).
2. Ph.D. Student, Dept. of Civil Engineering, Univ. of New Mexico, MSC01 1070, Albuquerque, NM 87131; formerly, Postgraduate Student, School of Civil Engineering, College of Engineering, Univ. of Tehran, 16 Azar Ave., P.O. Box 11155-4563, Tehran, Iran.