Simple Estimation Method of Building Deformation Using Two Seismometers without Precise Time Synchronization

Abstract

This paper proposes a method for calculating the maximum drift angle between seismometers using two seismometers installed on the first and upper floors of a building. With the wide-area expansion of the proposed method in mind, the seismometers aim to be able to evaluate even with the measurement accuracy of an accelerometer such as that built into a smartphone. Structural details about a building, time synchronization by the wired connection between two seismometers and a logger are not required. However, the seismometers must have a synchronization accuracy of time difference between the internal clocks by communication with NTP server, and must be corrected to the predetermined sampling frequency. An equivalent SDOF model estimates the response of a building. Primary natural angular frequency and damping ratio at the time of maximum response, which are unknown in the basic formula for calculating horizontal deformation between the seismometers, are solved from the peak of Fourier amplitude ratio obtained from acceleration records on the upper and lower floors. The features of this paper are to use elastic primary natural frequency evaluated at the end of the previous earthquake, and to narrow down primary natural frequency at the time of maximum response from a large number of peaks by dividing the acceleration records at regular intervals. The evaluation accuracy by the proposed method was verified using the results of four full-scale shaking table tests of S and RC structures carried out by E-Defense. As the results of the verification, it was confirmed that the measured values of the laser displacement gauge used in the tests and the evaluation results of the proposed method are almost consistent in the range from elastic region to plastic region. This verification is limited to the verification of a well-shaped building easily induced to primary mode, and the case where residual deformation and torsional deflection are small. Application to seismic motion where the principal motion continues for a long time, to buildings that are greatly affected by the soil-structure interaction effect, and to buildings of various shapes, as well as the solution of the maximum story drift angle, which is an important index for the damage degree of buildings, are out of the scope of this paper.