1. Professor, Dept. of Civil and Environmental Engineering, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milan, Italy (corresponding author).
2. Professor, Fazlur R. Khan Endowed Chair, Dept. of Civil and Environmental Engineering, Engineering Research Center for Advanced Technology for Large Structural Systems, Lehigh Univ., 117 ATLSS Dr., Bethlehem, PA 18015.