[1] Univ Pavia, Dipartimento Ingn Civile Architettura, I-27100 Pavia, Italy
[2] Iowa State Univ, Dept Mech Engn, Ames, IA 50011 USA
[3] CNR, Ist Matemat Appl & Tecnol Informat, I-27100 Pavia, Italy
[4] Tech Univ Munich, Inst Adv Study, D-85748 Garching, Germany