UFC 3-220-01N
15 AUGUST 2005
CHAPTER 12
DESIGN FOR EQUIPMENT VIBRATIONS AND SEISMIC LOADINGS
12-1
INTRODUCTION
12-1.1
Introduction. 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 retreated in
this action. Design of a foundation system incorporates the equipment lading,
subsurface material properties, and geometrical proportions in some analytical
procedure.
12-1.1.1
Vibration Criteria. Figure 12-1 shows some limiting values of vibration
criteria for machines, structures, and personnel. On this diagram, vibration
characteristic: 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 labeled in displacement (inches), and peak acceleration values are
read along the other set of diagonal lines and labeled 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 50 mm (2 in) 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.
12-1.1.2
Equipment Vibration Criteria. For equipment vibration, 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 0.15 g alive 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 0.25 mm (0.1 in) per second occurs for smooth, well-balanced
equipment; and less than 0.025 mm (0.01 in) per second represents very smooth
operation.
12-1.1.3
Vibration Affect on Personnel. Figure 12-1 also includes peak velocity
criteria for reaction of personnel to steady-state abrasions. Peak velocities greater than
0.25 mm (0.1 in) per second are "troublesome to persons," and peak velocities of 0.025
mm (0.01 in) per second are just "barely noticeable to persons." It is significant that
persons and machines respond to equivalent levels of vibration. Furthermore, persons
may notice vibrations that are about 1/100 of the value related to safety of structure.
12-1.2
Single Degree of Freedom, Damped Forced Systems. Vibrations of
foundation-soil systems can adequately be represented by simple mass-spring-dashpot
systems. The model for this simple system consists of a concentrated mass, m,
supported by a linear elastic spring with a spring constant, k, and a viscous damping
unit (dashpot) having a damping constant, c. The system is excited by an external
12-1
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