1. Civil Eng. Dept., Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisbon, Portugal (E-mail: didia.covas@civil.ist.utl.pt; helena.ramos@civil.ist.utl.pt)
2. Civil and Environ. Eng. Dept., Imperial College, Imperial College Road, SW7 2BU, London, UK (E-mail: n.graham@ic.ac.uk; c.maksimovic@ic.ac.uk)