1. Professor, Dept. of Civil Engineering, Univ. of Coimbra, Polo II, 3030-788, Coimbra, Portugal.
2. Research Assistant, National Laboratory of Civil Engineering, Avenida do Brasil 101, 1700-066, Lisbon, Portugal.
3. Ph.D. Student, Dept. of Civil Engineering, Univ. of Coimbra, Polo II, 3030-788, Coimbra, Portugal.
4. Professor, Dept. of Civil Engineering, Polytechnic Institute of Coimbra, Quinta da Nora, 3030-199, Coimbra, Portugal..