Page 67 - Dynamic Loading and Design of Structures
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Figure 2.17 Ductility factor µ, for an elastoplastic SDOF system as a function of ratio td/T
(2.52)
Next, Figure 2.18(b) depicts a simple rigid foundation on the ground, which is modelled by
two springs. The equations of motion, assuming small foundation rotation angle , are
(2.53)
where Mt is the torque on the foundation and I is its mass moment of inertia. We observe that
the above equations are not coupled, which implies that we do not have a true two DOF
system; rather, we have a system which can execute two independent motions, namely a
translation y and a rotation about its centre of mass.
