1. Ph.D. Candidate, Dept. of Structural Analysis and Design, Univ. of Naples Federico II, Via Claudio 21, Naples, P.O. Box I-80125, Italy. E-mail: glignola@unina.it
2. Assistant Professor, Dept. of Structural Analysis and Design, Univ. of Naples Federico II, Via Claudio 21, Naples, P.O. Box I-80125, Italy. E-mail: aprota@unina.it
3. Full Professor, Dept. of Structural Analysis and Design, Univ. of Naples Federico II, Via Claudio 21, Naples, P.O. Box I-80125, Italy. E-mail: gamanfre@unina.it
4. Full Professor, Dept. of Structural Analysis and Design, Univ. of Naples Federico II, Via Claudio 21, Naples, P.O. Box I-80125, Italy. E-mail: cosenza@unina.it