IDENTIFICATION OF ROTATIONAL INPUT MOTION AND DAMPING RATIO USING HORIZONTAL ACCELERATION RECORDS

In the seismic design of buildings, setting the damping ratio is of considerable importance, as this parameter greatly affects the prediction accuracy of building behavior during earthquakes. To this end, several studies have been carried out to identify the damping constants of buildings using earthquake records. Previous studies have indicated that it is important to consider the rotation input of building foundations when identify calculating the damping ratio using earthquake records. However, in most buildings, the rotational acceleration of the foundation has not been recorded. Therefore, it is difficult to identify the damping ratio considering the rotational acceleration. In this study, the feasibility of concurrently identifying the rotational input motion and damping ratio is examined. First, a method to identify the rotational input motion and damping ratio from horizontal acceleration records using modal iterative error correction is proposed. Then, the accuracy of the proposed method is examined using example problems. The main findings of this study are as follows: (1) A method to identify the rotational input motion and the damping ratio from horizontal acceleration records using a modal iterative error correction method is proposed. The modal iterative error correction method is based on inverse analysis, which addresses the inverse problem using many local stationary solutions. (2) Using shaking table test results as an example, the proposed method is used to determine the damping ratio of building models and rotational acceleration time histories inputted to building foundations. As a result, the damping ratio and rotation input time history could be calculated using the proposed method, which reproduced the horizontal acceleration records obtained from the shaking table tests with high accuracy. In addition, the calculated rotational input roughly agreed with the rotational input records of the test and the calculated damping ratio agreed well with the values determined in the case with known rotational input. (3) However, depending on the amount of perturbation set and the filtering method used, even if the horizontal acceleration can be reproduced, the calculated damping ratio may vary. Setting an appropriate amount of perturbation and selecting a suitable pre-filtering method to reduce this variation and identify a damping ratio with higher reliability is another problem of particular importance.