1. Ph.D. Candidate, Dept. of Civil and Environmental Engineering, Imperial College London, London SW7 2AZ, U.K. (corresponding author).
2. Professor of Structural Engineering, Dept. of Civil Engineering, KU Leuven, 3000 Leuven, Belgium.
3. Professor of Structural Engineering, Dept. of Civil and Environmental Engineering, Imperial College London, London SW7 2AZ, U.K.
4. Professor of Structural Engineering, Dept. of Civil Engineering, Univ. of Hong Kong, Pokfulam Rd., Hong Kong, China.