1. Assistant Professor, Dept. of Structural, Building, and Geotechnical Engineering, Politecnico di Torino, 10129 Turin, Italy (corresponding author).
2. Full Professor, Dept. of Structural Engineering, Univ. of California, San Diego, La Jolla, CA 92093.
3. Associate Professor, Dipartimento di Ingegneria Civile, Ambientale, Aerospaziale, dei Materiali, Univ. of Palermo, 90128 Palermo, Italy.