1. Full Professor, Dept. of Structural Engineering, Univ. of Pisa, Via Diotisalvi 2, 56126 Pisa, Italy.
2. PhD Student, Dept. of Structural Engineering, Univ. of Pisa, Via Diotisalvi 2, 56126 Pisa, Italy.
3. Assistant Professor, Dept. of Structural Engineering, Univ. of Pisa, Via Diotisalvi 2, 56126 Pisa, Italy (corresponding author).