1. Associate Professor, Dept. of Civil Engineering, Univ. of Minho, Campus de Azurém, Guimarães 4810-058, Portugal (corresponding author). E-mail: barros@civil.uminho.pt
2. Assistant, Dept. of Civil Engineering, Univ. of Minho, Campus de Azurém, Guimarães 4810-058, Portugal. E-mail: epereira@civil.uminho.pt
3. Researcher, Civitest Company, Celeirós, Braga 4705-414, Portugal. E-mail: simaopfsantos@civitest.pt