Equalizing Irregular Earthquake Loading to Harmonic Loading for Liquefaction Study

Liquefaction triggered by earthquakes is a source of damage to structures resting on loose to medium sandy soils. During earthquakes soil structures and the ground are subjected to vibratory excitations which are to a high degree erratic and extremely irregular. The magnitude of shear stress that is applied to a soil element in a real earthquake will, therefore, vary at random from one second to another. In order to evaluate the effect of such randomness, averaging procedures have been employed. In this averaging method a complex stress time history can be converted to an equivalent number of constant harmonic stress cycles. The equivalent load pattern thus determined has been considered as a representative load. This concept tends itself considerably to the simplification of the laboratory method. The soil selected for this thesis is known as Firouzkouh Sand No. 161, that exerted by load pattern that recorded in Kojaeli earthquake in 1999. Finally by using the stress averaging method, the reduction coefficient of stress is proposed and compared to those of existing studies and codes.