1. Assistant Professor, Dept. of Civil Engineering, Univ. of Messina, C.da di Dio, 98166 S. Agata, Messina, Italy (corresponding author).
2. Full Professor, Dept. of Civil and Environmental Engineering, Univ. of Catania, V.le A. Doria 6, 95125 Catania, Italy.
3. Engineer, Dept. of Civil and Environmental Engineering, Univ. of Catania, V.le A. Doria 6, 95125 Catania, Italy.
4. Assistant Professor, Dept. of Civil and Environmental Engineering, Univ. of Catania, V.le A. Doria 6, 95125 Catania, Italy.