Modal Identification of 1:2 Scaled Model of a 4-Story Steel Structure by Impulse Excitation

摘要

The advantages of in-situ tests recommend them in the verification of mathematical models of the structure, as well as for basic input data to forecast its behavior during an earthquake. In-situ vibration tests can be conducted by different methods including ambient vibration test. The ambient vibration tests rely on natural excitations, consequently, it is recommended to perform impulsive test for identifying the hidden dynamic characteristics of the system. The impulse test is based on measuring free vibration of the structure affected by impulse on a pre-determined point of the system. In this article, the results of Impulsive test on 1:2 scaled model of a 4-story steel structure have been represented. In order to record the response of the model, there has been used ten 3-component CMG-6TD seismometers, in which, 2 seismometers has been installed in each floor. Also, for recording input vibration, there have been used 2 sensors at foundation level. The responses of the structure to ambient and impact vibrations were recorded continuously for about 24 hours and in this period the sensors were connected to GPS device in order to synchronization. In this test, four impulse on the forth floor in N-S, E-W and vertical directions were applied. The four-spectral method; PSD (power spectra density), CSD (Cross Power Spectra), CS (Coherence Spectra) and PCSD (phase of Cross Spectral Density) was used for processing the recorded data. In this paper, the results of the tests will be presented and their effect on calibrating the numerical model of the structure will be discussed.