HYBRID TIME AND FREQUENCY DOMAIN TECHNIQUE ON MODAL IDENTIFICATION USING AMBIENT VIBRATION TESTS

In this paper, in order to identify the modal properties of a structure based on the ambient vibration monitoring, an innovative method for modal identification, called Hybrid Time and Frequency Domain Analysis, is described and a full scale test is presented. The method consists of frequency domain analysis for natural frequencies and modal shapes identification; and time domain analysis for the damping estimation. The methodology was tested in a 5 story steel frame structure constructed at the Disaster Prevent Research Institute, Kyoto University, Japan, using ambient vibration testing. The dynamic response was measured with simultaneous sensors in every floor, including ground. The modal shapes results were compared with the FEM and with previous results obtained from monitoring under forced vibration. For the damping estimation, free vibration results were compared with the ambient vibration test. The system identification obtained under ambient vibration tests are in very good agreement with the forced and free vibration tests and with the analytical results.