1. Assistant, Dept. of Civil Engineering, Univ. of Minho, Campus de Azurém, 4810-058 Guimarães, Portugal (corresponding author). E-mail: epereira@civil.uminho.pt
2. Associate Professor, Dept. of Civil Engineering, Univ. of Minho, Campus de Azurém, 4810-058 Guimarães, Portugal. E-mail: barros@civil.uminho.pt
3. Assistant Professor, Dept. of Civil Engineering, Univ. of Minho, Campus de Azurém, 4810-058 Guimarães, Portugal. E-mail: aires@civil.uminho.pt