1. Associate Professor, Federal Univ. of Ceará, Brazil.
2. Reader, Imperial College, London.
3. Professor, Dept. of Civil Engineering, Federal Univ. of Rio Grande do Sul, Ave. Osvaldo Aranha 99, 3 Andar, CEP 90035-190 Porto Alegre, Rio Grande do Sul, Brazil (corresponding author). E-mail: consoli@ufrgs.br