Dynamic properties of existing RC buildings using measurements of ambient vibrations

摘要

In order to know the general dynamic behaviour of existing building structures in the urban area of Lisbon city (Portugal) and to obtain natural period and damping predictors in the range of small amplitudes, we analyze the period dependencies of damping ratio using full-scale data on 37 reinforced concrete (RC) buildings, with a number of stories between 4 and 29. We recorded building vibration measurements, excited by ambient vibration, at the top of buildings or at the center of plan on the roof floor, the velocity of displacement of building structure was measured and Fast Fourier Transformation was applied to every record in order to compute Fourier spectrum. The relationship between the natural period for swaying motion (T) and the number of stories (N) obtained is T = 0,043 N with a correlation factor r = 0,98. The Random Decrement Technique has been applied to determine the damping factor of RC buildings and the average value of damping factors in Lisbon city is h = 2.6+ - 1.7 percent. From correlation between natural period and damping factor, we are obtained the damping predictor given by h T = 1.1 + 0.6 percent. Finally, the dynamic behaviour of a prototype isolated RC building has been evaluated by using simulation response, strong motion records and ambient vibrations.