1. Civil Engineer, Professor, Dept. of Civil Engineering, Engineering Superior Institute of Coimbra, Rua Pedro Nunes, Quinta da Nora, 3030-199 Coimbra, Portugal. E-mail: capitao@isec.pt
2. Civil Engineer, Professor, Dept. of Civil Engineering, Faculty of Sciences and Technology, Univ. of Coimbra, Pinhal de Marrocos, Polo II, 3030 Coimbra, Portugal. E-mail: picsan@dec.uc.pt