Q1 A mass of m, supported at the structure shown in Fig Q1 can be modeled as a single degree of freedom system of mass (m), spring stiffness (k), damper

(c), in vertical direction. The flexural rigidity of both beam AB and CD are El Nm², The shear stiffness of the two beams AB and CD are both 12EI/L', The column between the two beam AB and CD can be consider as rigid. Please work out the natural frequency of the structure. (30 Marks)