1. Assistant Professor, Dept. of Civil and Environmental Engineering, Computer Science, Constructions, and Applied Mathematics, Univ. of Messina, 98166 S. Agata, Messina, Italy (corresponding author).
2. Assistant Professor, Dept. of Civil Engineering and Architecture, Univ. of Catania, 95125 Catania, Italy.
3. Full Professor, Dept. of Civil Engineering and Architecture, Univ. of Catania, 95125 Catania, Italy.