1. Assistant Professor, Technical Univ. of Lisbon-IST, Civil Engineering and Architectural Dept., Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal. E-mail: nguerra@civil.ist.utl.pt
2. Professor, Univ. of Oporto-FEUP, Civil Engineering Dept., R. Dr. Roberto Frias, 4200-465 Oporto, Portugal. E-mail: scardoso@fe.up.pt
3. Professor, Univ. of Oporto-FEUP, Civil Engineering Dept., R. Dr. Roberto Frias, 4200-465 Oporto, Portugal. E-mail: mfern@fe.up.pt
4. Professor, Univ. of Minho, Civil Engineering Dept., Azurém, 4800-058 Guimarães, Portugal. E-mail: agc@civil.uminho.pt