Modal identification of a four-story reinforced concrete building under renovation by using ambient vibration measurement

This paper presents the identification and discussion of changes in modal parameters of atypical four-story reinforced concrete building undergone renovation. The aim of this study is to apply and evaluate the procedures of the well-established modal parameter identification technique using ambient vibration measurement. Correlation function is first used to transform ambient vibration response into impulse response and then modal parameters, i.e. frequencies, damping ratios, and mode shapes, are identified by Eigensystem Realization Algorithm (ERA). The study shows that the major difficulty in identification of modal parameter from ambient vibration can be attributed to low signal-to-noise ratio, especially in higher frequency range. It was found that reliable estimation of frequencies of the building could be obtained whereas larger variation can be observed in case of damping ratio. Changes in modal frequencies of the building can be clearly observed in agreement with the changes in structural configuration.