The 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 foundation.
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 sinusoidally.
- 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.