1. Lecturer, Polytechnic Institute of Castelo Branco, Av. Pedro Álvares Cabral, 12, Castelo Branco, 6000-084, Portugal.
2. Professor, Dept. of Civil Engineering, FCTUC, Polo II, Univ. of Coimbra, Coimbra, 3030-290, Portugal (corresponding author).
3. Researcher, LNEC—National Laboratory of Civil Engineering, Av. do Brasil, 101, Lisboa, 1700-066 Lisboa, Portugal.