1. Ph.D. Student, Dept. of Civil Engineering, Univ. of Minho, Azurém, 4800-058 Guimarães, Portugal (corresponding author).
2. Associate Professor, Dept. of Civil Engineering, Univ. of Minho, Azurém, 4800-058 Guimarães, Portugal.
3. Full Professor, Dept. of Civil Engineering, Univ. of Minho, Azurém, 4800-058 Guimarães, Portugal.