1. Assistant Professor, Dept. of Structural Engineering, Milan Univ. of Technology (Politecnico), P.zza L. da Vinci 32, 20133 Milano, Italy. E-mail: francesco.calvetti@polimi.it
2. Associate Professor, Dept. of Structural Engineering, Milan Univ. of Technology (Politecnico), P.zza L. da Vinci 32, 20133 Milano, Italy. E-mail: claudio.diprisco@polimi.it
3. Professor, Dept. of Structural Engineering, Milan Univ. of Technology (Politecnico), P.zza L. da Vinci 32, 20133 Milano, Italy. E-mail: roberto.nova@polimi.it