Giorgio Mariani is a graduated Structural Engineer at University of Pisa, since February 2001. Starting from January 2002, he had been attending for three years the PhD Course in Structural Engineering, still at University of Pisa, under the guide of Professor Mauro Sassu. During this period he carried out some tutoring activity within the Course in Structural Mechanics hold by Professor F. Cafarella, and this circumstance gave him the opportunity to get involved in theoretical matters, regarding the subjects dealt with in the Course itself. Some of the results obtained form the object of the paper featured in the present site. He is working nowadays as a professional Structural Engineer in Lucca, as part of the associated firm RIMA, and he is still performing some tutoring activity at University of Pisa, in the Structural Design Course run by Professor M. Sassu.