1. Teaching Fellow, Dept. of Civil, Environmental, and Geomatic Engineering, Univ. College London (UCL), Gower St., London WC1E 6BT, U.K. (corresponding author).
2. Associate, Arup, Suite 700, San Francisco, CA 94105.
3. CEng MIMechE, Principal, Arup Fellow, Arup, Beta Building, Naritaweg 118, 1043 CA, Amsterdam, The Netherlands.
4. Professor, Dept. of Civil and Environmental Engineering, Stanford Univ., Blume Center, Building 540, Stanford, CA 94305.