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A method for an evaluation of the building structure response reduction by soil‐structure interaction (SSI) based on the seismographs of the soil‐structure system is presented. In the proposed method, a simplified SSI model is employed, and the parameters of model are determined by system identification. For system identification, both the inertial interaction (II) and kinematic interaction (KI) are considered. The method that indicates a reduction in the structure response by II and KI separately is also presented. The proposed procedures are applied to the observed records of the 2011 off the Pacific coast of Tohoku Earthquake. The findings demonstrate that the reduction effect of II is reduced when the response of building structure enters the inelastic range, and vice versa. In the superstructures with pile foundations, the reduction effects of KI are relatively smaller than those of II.

In order to clarify effects of earthquake motion and aging on dynamic characteristics of wooden houses, earthquake records at a seismically isolated wooden house for 10 years are summarized. The predominant period and amplification factor of the 2-story superstructure are compared, based on acceleration amplitude of earthquake motion, drift angle of first story, and time after completion. The predominant period is longer with increasing the acceleration amplitude and the story drift angle. The average predominant period for two years after 8 years is longer than that of first two years by 2.9-12.2%. The dependency of acceleration amplitude and time on the amplification factor is not clear.

To make sure the relationship between strong ground motions and building damages, dynamic earthquake response analyses of a building, which had a slight damage during the 2007 Niigata-ken Chuetsu-oki earthquake, are performed. Earthquake records at ground surface have been observed by the K-NET system near the building. Also the building responses were observed during after-shock. The analysis model of the building is estimated based on results of a push-over analysis. Sway and rocking impedances are also installed in this model. The predominant frequency of the building in elastic condition is corresponding to that in after-shock observation. It is demonstrated that the response of the building, which is calculated considering the nonlinear characteristics of soil and building during the main-shock, is larger than the estimated response based on the damage situation of the building.

This paper proposes a response spectrum method (RSM) for evaluating nonlinear amplification of surface strata (SS) overlying an engineering bedrock (EBR). The proposed RSM follows the procedures below. (1) Represent the response characteristics of SS on EBR by a multi-lumped mass model with shear springs and damping coefficients. (2) Calculate a period T1, a mode shape {U1} and a modal damping factor ƒA1 for the first vibration mode. (3) Evaluate the equivalent shear wave velocity Vse of SS. (4) Evaluate the amplification factor R1 of the surface to EBR at T1 using the Haskell matrix of two strata consisting of an equivalent SS with Vse and ƒA1 on EBR. (5) Evaluate the displacements in SS from R1{U1}, and hence evaluate the shear strains. (6) In accordance with nonlinear relations between shear modulus (G), damping factors (h) and shear strains, replace soil constants G and h by those corresponding to strains. (7) Return to step (1) with revised G and h. Iterate these procedures until T1 becomes stable. (8) After T1 is converged, calculate the response distributions in SS. The results obtained by the proposed RSM are compared with those by “SHAKE” in terms of the response spectrum at the surface as well as distributions of displacement, shear wave velocity and damping factor in SS. The applicability of the proposed RSM for evaluating the nonlinear amplification of SS is confirmed through the comparative studies.