ESTIMATING KINEMATIC INTERACTION OF RAFT FOUNDATIONS FROM EARTHQUAKE RECORDS AND ITS EFFECTS ON STRUCTURAL RESPONSE

A practical method for estimating kinematic interaction from earthquak e records is presented. The kinematic interaction is characterized by a two-parameter model and these parameters can be estimated by using a frequency-domain systems identification method. The simple model can be used to model both wave passage effects and the effects of incohere nt wave fields. Numerical simulation tests show that kinematic interac tion parameters can be estimated to their best accuracy by using build ing base responses and the free-field excitation and can also be estim ated by using building responses, base responses and the free-field ex citation. The method was applied to two buildings with raft foundation s and it was found that kinematic interaction was significant during e arthquakes. Published theoretical models (wave passage effect) for ver tically incident SH waves can be used to estimate the transfer functio ns up to 4-5 Hz and the models for horizontally propagating waves unde r-predict the estimated transfer functions by a significant amount at frequencies beyond about 1-2 Hz. Theoretical models for a massless rig id foundation under the excitation of an incoherent wave field predict the general trend of the estimated transfer function reasonably well over a large frequency range. The results of numerical examples show t hat the recorded response spectral attenuation of basement records at high frequencies with respect to the free-field is mainly caused by ki nematic interaction, while the changes in storey shear and overturning moment in a structure due to soil flexibility are mainly the results of inertial interaction. (C) 1998 Elsevier Science Limited.