Geotechnical engineers frequently come across two types of problems in relation to the analysis and design foundations namely (i) foundation subjected to static loads and (ii) foundation subjected to dynamic loads. the characteristic feature of a static load is that for a given structure the load carried by the foundation at any given time is constant in magnitude and direction e.g. dead weight of the structure. live loads such as weight of train on a bridge and assembly of people in a building are also classified as static load. the characteristic feature of a dynamic load is that it varies with time. dynamics load on foundation and engineering structures may act due to earthquakes, bomb blasts, operation of machines, pile driving, quarrying, fast moving traffic, wind or sea waves action.
The nature of each dynamic load is different from another. purely dynamic loads do not occur in nature. loads re always combinations of static and dynamic loads. static loads are caused by the dead weight of structure, while dynamic loads may be caused through the sources mentioned above.
1.2 Earthquake Loading
Vibration of earth’s surface caused by waves coming from a source of distribunce inside the earth are described as earthquakes and are one of the most destructive forces that nature unleashes on earth. when, at any depthbelow the ground surface, the strain energy accumulted due to deformation in earth mss exceeds the resilience of the storing material, it gets release through rupture. the energy thus released is propogated in the form of waves which impart enrgy to the media through which they pass and vibrate the structure standing on the earth’s surface. the point inside the earth mass where slipping or fracture begins in termed as focus and the point just above the focus on the earth’s surface is termed as epicentre. The position of the focus is determined with the help of seismograph records utilising the average velocities of different waves and time difference in reaching the waves at the ground surface.
Nb : This Material was taking from Dr. Swami Saran’s Book “Soil Dynamics and Machine Foundations” and being continued…