1. Professor, Dept. of Civil and Environmental Engineering, Univ. of Perugia, via G. Duranti 93, 06125 Perugia, Italy.
2. Assistant Professor, Dept. of Civil and Environmental Engineering, Univ. of Perugia, via G. Duranti 93, 06125 Perugia, Italy.
3. Post Graduate Student, Dept. of Civil and Environmental Engineering, Univ. of Perugia, via G. Duranti 93, 06125 Perugia, Italy.