tures having the same mass will have the higher vibration frequency and the shorter vibration period. Similarly, the lighter (less mass) of two structures having the same stiffness will have the higher vibration frequency and the shorter vibration period.
Damped Structures
Figure 9 shows the free vibration response of two one-story structures, identical in all respects except that one is undamped and the other includes a viscous damper. Free vibration of both systems results from an initial displacement u(O) and velocity u(O) imparted to the mass. The displacement-time plots for both
systems start at t = 0 with the same ordinate and slope. The
displacement amplitude of the undamped structure is the same in all vibration cycles, but the damped structure oscillates with amplitude decreasing with every cycle of vibration.
The natural period T 0, circular frequency w0, and cyclic frequency f0 of vibration of the damped structure are interrelated as