Abstract
The paper presents results from an experimental program implemented for three representative buildings in Bucharest metropolitan area and aimed to explore the potential of various dynamic identification methods in providing information about building state changes. The objective is to establish reference values of potential use in rapid earthquake damage detection systems. Each of the selected buildings was designed according to a different seismic code, in force at the time of its construction. The methods employed for this study were: the analysis of Fourier spectra, the analysis of the transfer function and the random decrement technique. To validate the results, the fundamental periods of vibration determined experimentally were compared with the corresponding values predicted by the empirical formulas specified in the corresponding editions of the Romanian seismic code. The results revealed consistent values for both the fundamental period and the damping ratio of the buildings. However, small variations of the two parameters were identified, depending on the time the recordings were performed, noise sources and levels and building occupancy. The results, in terms of validated data on the dynamic characteristics of Romanian building stock and of assessment of methods performance, add up to the information pool needed for the development of countrywide pre- and post-earthquake assisted decision tools.
Highlights
Vibration monitoring of buildings represents an important source of information about their state, in terms of material degradation, structural changes or damage [1, 2]
The results show that the IFA building is founded on a soil having a fundamental period of vibration of approximately 1.3 seconds, double than the fundamental period of the building
A study on ambient vibration measurements performed on three multistory buildings in Bucharest area was presented, in which values of dynamic characteristics obtained by three different methods (Fourier spectra, transfer function and random decrement technique) were compared and analyzed in correlation with various factors, as measurement time and retrofitting history, whenever applicable
Summary
Vibration monitoring of buildings represents an important source of information about their state, in terms of material degradation, structural changes or damage [1, 2]. The basic idea of ambient vibration monitoring is to rapidly detect changes in the building’s dynamic characteristics (natural periods, damping) and to reliably relate these changes to potential damage or degradation. One of the simplest methods used for detecting structural damage in buildings is related to the fluctuation of its fundamental period (frequency) [3,4,5,6]. Two key parameters used in seismic design and that control the building’s response during an earthquake are the fundamental period and the damping. The influence of these parameters can be explained by reducing the building to an inverted pendulum, with a time-varying acceleration (the ground motion, üg(t)) applied at its base. With ω denoting the angular frequency and ξ – the damping ratio, Equation 1 can be written:
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