1. Assistant Professor, Dept. of Civil and Environmental Engineering, Princeton Univ., Princeton, NJ 08540 (corresponding author). E-mail;
2. Partner, Ney and Partners, sa, Chaussée de la Hulpe 181, B-1170 Brussels, Belgium.
3. Senior Lecturer, Dept. of Architecture and Civil Engineering, Univ. of Bath, Claverton Down, Bath BA2 7AY, U.K.