1. Associate Professor, Dept. of Civil Engineering, Univ. of Udine, Via delle Scienze 208, 33100 Udine, Italy (corresponding author). E-mail: stefano.sorace@uniud.it
2. Researcher and Assistant Professor, Dept. of Civil Engineering, Univ. of Florence, Via di S. Marta 3, 50139 Florence, Italy. E-mail: terenzi@dicea.unifi.it