1. Lecturer, Dept. of Civil and Natural Resources Engineering and Dept. of Mechanical Engineering, Univ. of Canterbury, Christchurch 8041, New Zealand (corresponding author).
2. Full Professor of Structural Engineering, Dept. of Structural and Geotechnical Engineering, Sapienza Univ. of Rome, 00185 Rome, Italy; Dept. of Civil and Natural Resources Engineering, Univ. of Canterbury, Christchurch 8041, New Zealand.
3. Professor, Dept. of Mechanical Engineering, Univ. of Canterbury, Christchurch 8041, New Zealand.