familiarity with the Foundations subjected to static loads has been very common.
But, in some cases the foundations are also subjected to the dynamic loads. The
resulting dynamic forms of loads may be from numerous causes like vibratory
motion of machines, impacts from hammering, vehicle access/movement,
earthquakes, waves, winds, cyclones, nuclear blasts, mining explosions, pile
driving process and many more. The spread or transfer of these dynamic
loadings/vibrations to the foundations and their consequences on the soil strata
below can be determined using the principle of soil dynamics and theory of
vibrations. The type of foundations used to encounter such dynamic
forces/vibrations caused by machines used is known as “machine foundations”. The
dynamic forces are transmitted to the foundation supporting the machine.
Generally the moving, shaking components of the machines are balanced, yet there
is always some unbalanced condition in actual practice which results the
eccentricity of rotating parts. Thus, it is very essential that the machine
foundations require satisfying the criteria of dynamic loading plus static
loading that exists already.A machine foundation necessitates a special concern
as they are designed to transmit dynamic loads to soil strata in addition to
static loads. Event thought the dynamic loading/forces/vibrations due to machine
operations is normally small in comparison to the static weight/loads from the
machine and the supporting foundation. In machine foundations the dynamic loads
are applied continually over a lengthier period of timing however since its
magnitude is comparatively small so the soil behavior is found to be
essentially elastic, otherwise deformations tends to increase after each cycle
of loading and may lead to be incredibly higher that becomes unacceptable. on
top of the natural frequency of the machine foundation soil system the amplitude
of vibration of the machine during its working frequency is the most vital
parameter to be considered and determined while designing of a machine
To know the efficient constructions of machine foundations it is very essential
to have brief, effective ideas regarding the types of machines based on speed.
Principally there are three sorts of machines:
- Machines producing periodic unbalanced force, like the reciprocating engines
and compressors. The speed of these machines is usually lower than 600
r.p.m. In these types of machines the rotary motion of the crank is
transformed into the translatory motion, here the unbalanced force varies
- Machines producing impact loads, like the forge hammers and punch presses.
In such machines the dynamic force/vibrations attains a peak limit in very
short instant and then expires out steadily/gradually. Here the response is
a pulsating curve which vanishes before occurrence of next pulse. The speed
seen is generally between 60-150 blows per minute.
- Lastly the high speed machines, like turbines and rotary machines. These
machine rotating speeds are very high sometimes even higher than 3000 r.p.m.