Table 1: Names adopted for models considering the stiffness of the connection.

kb Model I Model II Model III
M1 M2 M3
50 M1-50 M2-50 M3-50
25 M1-25 M2-25 M3-25
12.5 M1-12.5 M2-12.5 M3-12.5
6.25 M1-6.25 M2-6.25 M3-6.25