1. Professor, School of Engineering, Univ. of Aberdeen, Aberdeen AB24 3UE, UK (corresponding author).
2. Professor, Dept. of Civil and Environmental Engineering, Politecnico di Milano, Piazza Leonardo Da Vinci, 32, 20133 Milan, Italy.
3. Associate Professor, Dept. of Civil and Environmental Engineering, Univ. of Auckland, Auckland 1142, New Zealand.
4. Reader, School of Engineering, Univ. of Aberdeen, Aberdeen AB24 3UE, UK.