Recently, the business continuity plan (BCP) is becoming a leading subject in the world and is being discussed with great concern in the construction and operating process of various built environments. In response to BCP, the structural health monitoring (SHM) has drawn much attention for evaluating the status of buildings and reducing post-earthquake impacts on our society. In developing SHM, the system identification (SI) methodologies, categorized as methods for inverse problems, play a critical role and the modal SI and physical SI are two major well-known branches. The physical SI has the advantage that the stiffness and/or damping coefficients of the structural model can be recovered directly and is well suited to the design of passive control systems. This is also quite useful for the damage detection. Although the physical SI is preferred in SHM, its development is quite limited and slow due to the strict requirement on multiple measurements or the necessity of complicated mathematical manipulation. In particular, investigation on physical SI of three-dimensional (3D) building structures with stiffness or mass eccentricities are more limited.
This paper proposes a new method of frequency-domain physical-parameter system identification of three-dimensional building structures with stiffness eccentricity, which accompany torsional vibration. The two-directional story stiffnesses in the 3D building structure are identified from the horizontal accelerations recoded at the top and first floors. The proposed method has three processes. In the first process, equations of motion in the time domain are transformed into the frequency domain. The theoretical equations to identify the j-th two-directional story stiffnesses are derived from the dynamic equilibrium of the free body above the j-th story. In the second process, the responses on non-observation floors are evaluated from the horizontal accelerations recoded at the top and first floors with low-order modal shapes. In the last process, all responses are applied to the theoretical equations and the two-directional story stiffnesses are evaluated from the identification result near low-order natural frequency. Compared to the previous approaches, the proposed method has some features and advantages, which are as follows.
・ The proposed method is based on Fourier analysis method and avoids complicated mathematical manipulation.
・ The two-directional story stiffnesses in the 3D building structure can be identified from the horizontal accelerations recorded at the top and first floors of the building.
・ The data with high S/N ratio, which is selected based on low-order modal information, is used for the identification and this makes the proposed method robust for noise.
・ The two-directional story stiffnesses for each story can be identified independently. The identification result of one story doesn’t affect those of other stories.
The proposed method is demonstrated through numerical simulations and scaled experiments. Numerical examples, including the comparison with the numerical simulation results, demonstrated that the proposed method is reliable and possesses an acceptable accuracy. It should be remarked that identification results of story stiffnesses are quite stable near the low-order natural frequency and are robust for noise. However, it should be noted that the accuracy of low-order modal shapes used for the identification highly affect that of identification results. In experiments using scaled models, although the dependences to amplitude and input direction of ground motion were slightly confirmed, the reliability and accuracy of the proposed identification method were made clear.
