1. Professor of Structural Mechanics, Dept. of Structural Engineering and Geotechnics, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129, Torino, Italy (corresponding author). E-mail: alberto.carpinteri@polito.it
2. Researcher, Dept. of Structural Engineering and Geotechnics, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129, Torino, Italy. E-mail: giuseppe.lacidogna@polito.it