1. Full Professor of Design of Structures, DICAM, Univ. of Palermo, Viale delle Scienze, Palermo 90128, Italy (corresponding author).
2. Ph.D. Student, DICAM, Univ. of Palermo, Viale delle Scienze, Palermo 90128, Italy.
3. Professor of Design of Structures, DICAM, Univ. of Palermo, Viale delle Scienze, Palermo 90128, Italy.