a. Vibrations caused by steady state or transient loads may cause settlement of soils, excessive motions of foundations or structures, or discomfort or distress to personnel.  Some basic design factors for dynamic loading are treated in this section.  Design of a foundation system incorporates the equipment loading, subsurface material properties, and geometrical proportions in some analytical procedure.

b. Figure 17-1 shows some limiting values of vibration criteria for machines, structures, and personnel.

Response spectra for tibraton limits.
Figure 17-1.  Response spectra for tibraton limits.

On this diagram, vibration characteristics are described in terms of frequency and peak amplitudes of
acceleration, velocity, or displacement.  Values of frequency constitute the abscissa of the diagram and peak velocity is the ordinate.  Values of peak displacement are read along one set of diagonal lines and labelled in displacement (inches), and peak acceleration values are read along the other set of diagonal lines and labelled in various amounts of g, the acceleration of gravity.  The shaded zones in the upper right-hand corner indicate possible structural damage to walls by steady-state vibrations.  For structural safety during blasting, limit peak velocity to 2.0 inches per second and peak acceleration to 0.10g for frequencies exceeding 3 cycles per second.  These limits may occasionally have to be lowered to avoid being excessively annoying to people.

c. For equipment vibrations, limiting criteria consist of a maximum velocity of 1.0 inch per second up to a frequency of about 30 cycles per second and a peak acceleration of 0.15g above this frequency.  However, this upper limit is for safety only, and specific criteria must be established for each installation.  Usually, operating limits of equipment are based on velocity criteria; greater than 0.5 inch per second indicates extremely rough operation and machinery should be shut down; up to 0.10 inch per second occurs for smooth, well-balanced equipment; and less than 0.01 inch per second represents very smooth operation.

d. Figure 17-1 also includes peak velocity criteria for reaction of personnel to steady-state vibrations. Peak velocities greater than 0.1 inch per second are "troublesome to persons," and peak velocities of 0.01 inch per second are just "barely noticeable to persons." It is significant that persons and machines respond to equivalent levels of vibration.

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