Ground motions that are not influenced by the presence of structures are referred to as free fieldmotions. Free field motions are used in soil-structure interaction problems analyzed by Beam onNonlinear Winkler Foundation (BNWF) approach. Currently available one dimensional ground responseanalysis computer programs SHAKE, NERA and ONDA calculate free field motions due to seismicexcitation applied at bedrock. These computer programs being based on total stress concept do notconsider generation of excess pore water during seismic events and hence should not be used forseismic free field analyses of saturated cohesionless soil where liquefaction problems may occur. Thispaper illustrates an efficient use of a computer program called Cyclic 1D for predicting free field motionsat various layers in saturated sand deposit. The program Cyclic 1D that is based on effective stressconcept implements multi yield surface soil plasticity model in time domain. A detailed comparison of theresults obtained with Cyclic 1D is made against free field motions recorded in centrifuge tests. This paperalso describes values of Cyclic 1D model parameters that can be applied to free field analyses of soilstrata similar to the one used here.
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