1. Ph.D. Candidate, School of Mathematics, Computer Science and Engineering, Dept. of Civil Engineering, City, Univ. of London, London EC1V 0HB, UK.
2. Professor and Royal Academy of Engineering Pell Frischmann Chair, School of Mathematics, Computer Science and Engineering, Dept. of Civil Engineering, City, Univ. of London, London EC1V 0HB, UK (corresponding author).