Although the displacement resonant

Although the displacement resonant frequency is different from the damped or undamped natural frequencies, the difference is negligible for the degree of damping typical of structures-less than 4% if the damping ratio does not exceed 20%.
Figure 15 shows that the sharpness or width of the response curve in the vicinity of the resonant frequency depends on the damping in the system. The width at the "half-power point" (i.e.
at a value of D = Dmax ÷√2) is 2t as illustrated in Fig. 16.


External Force Due to Vibration Generator

Vibration generators (or shaking machines) have been developed to conduct forced vibration tests on full-scale structures (Hudson, 1970). Two equal eccentric weights rotating in opposite directions generate a unidirectional force varying sinusoidally with time. Two weights each of mass m rotating at a
radius (eccentricity) r at a frequency w (in rad /sec) would produce a force = 2m0rwsin wt. The amplitude of this force is proportional to w2in contrast to the constant amplitude of the external force considered in the preceding section. Thus, based on