Identification of Site Dynamic Properties for Soil-Structure Systems

Abstract

Conventional soil models with single spring and damping components can not properly simulate the frequency-dependent behavior of foundation soils. In this study, the foundation soil is modeled by a two-degrees-of-freedom mechanical model (2DOF) with eight integrated constant parameters. The 2DOF model provides a reasonable basis for the nonlinear dynamic analysis of soil-structure interaction (SSI) system in the time domain. To determine the values of the integrated parameters in the 2DOF model, a system identification technique using the extended Kalman filter (EKF) is developed in this study. To improve the computational accuracy and simplicity, the first order polynomial approximation is applied in the EKF procedure. A realistic identification example is given for two soil sites in Anchorage, Alaska. The recorded seismic data from two relatively long-period earthquakes, the Nanana earthquake (23rd October 2002) and the Denali earthquake (3rd November 2002), are used for the identification example. Results of the example demonstrate the feasibility and practicality of the proposed identification technique. Based on the identified integrated parameters, the site impedance functions and predominant frequencies can be estimated. The 2DOF soil model and the identification technique can be used in time-domain for nonlinear analysis of soil-structure interaction in various complex soil conditions. The identified parameters can be stored in a database for other similar soil conditions. Developing a broad database may provide an useful insight for investigating effects of SSI.