1. PhD Candidate, School of Engineering, Cardiff Univ., P.O. Box 925, Cardiff CF24 0YF, Wales, U.K. Present address: Assistant Professor, Dept. of Civil Engineering, Shahrood Univ. of Technology, Shahrood, Iran.
2. Professor, School of Engineering, Cardiff Univ., P.O. Box 925, Cardiff CF24 0YF, Wales, U.K. (corresponding author).