The system identification is regarded as the most basic technique for structural health monitoring to evaluate structural integrity. Although many system identification techniques that can extract mode information (e.g. mode frequency and mode shape) have been proposed so far, it is also desired to identify physical parameters (e.g. stiffness and damping). As for high-rise buildings subjected to long-period ground motions, the system identification for evaluating only the shear stiffness based on a shear model does not seem to be an appropriate solution to the system identification problem due to the influence of overall bending response. In this paper, a system identification algorithm using a shear-bending model is developed to identify both shear and bending stiffnesses. In this algorithm, an ARX (Auto-Regressive eXogenous) model corresponding to the transfer function for interstory accelerations is applied for identifying physical parameters. For the experimental verification of the proposed system identification framework, vibration tests for a 3-story steel mini-structure are conducted. The test structure is specifically designed to measure horizontal accelerations including both shear and bending responses. In order to obtain reliable results, system identification theories for two different inputs are investigated; (a) base input motion by a modal shaker, (b) unknown forced input on the top floor.

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A new stiffness identification method for a building structure is proposed in the case where the building includes an unknown vibration source. The stiffnesses above the vibration source are determined by the theory for the base input and those below the vibration source are obtained by the theory for the top forced input. The ratios between shear stiffnesses of lower consecutive stories can be obtained from the floor acceleration data and the ratios of the story rotational stiffness to the shear stiffness (SR stiffness ratio). The shear stiffness coefficients and the SR stiffness ratios can be obtained finally to satisfy the compatibility of lower natural frequencies. The validity of the proposed method is examined through numerical simulation and actual recorded data. Keywords : System identification, Structural health monitoring, Unknown vibration source, Bending-shear model, ARX model