1. Associate Professor, Dept. of Structural, Geotechnical and Building Engineering, Politecnico di Torino, 10129 Turin, Italy (corresponding author).
2. Graduate Research Assistant, Dept. of Structural, Geotechnical and Building Engineering, Politecnico di Torino, 10129 Turin, Italy.
3. Byron and Elvira Nishkian Professor of Structural Engineering, Dept. of Civil and Environmental Engineering, Univ. of California, Davis Hall, Berkeley, CA 94720-1710.