1. a Department of Civil Engineering , Instituto Superior Técnico (IST) , Av. Rovisco Pais, Lisboa , 1049-001 , Portugal E-mail:
2. b Department of Civil Engineering , Instituto Superior Técnico (IST) , Av. Rovisco Pais, Lisboa , 1049-001 , Portugal E-mail:
3. c Department of Civil Engineering , Instituto Superior de Engenharia de Lisboa (ISEL) , Portugal E-mail:
4. d National Lab of Civil Engineering (LNEC) , Av. do Brasil 101, Lisboa , 1799 , Portugal E-mail: