Monitoring the response and the back-radiated energy of a building subjected to ambient vibration and impulsive action: the Falkenhof Tower (Potsdam, Germany)

Abstract

The response of the soil-structure system near the Falkenhof Tower, Potsdam, Germany, has been monitored during the controlled explosion of a bomb dating to World War II. We installed eight 3-component velocimetric stations within the building and three in the surrounding area. We recorded several hours of seismic noise before and after the explosion, allowing the dynamic characterization of the structure both with ambient noise and forced vibration. We then compared the frequencies values and modal shapes of the structural modes evaluated both by analysing in the frequency domain the transfer functions and in the time-domain the different signals.Moreover, we carried out an interferometric analysis of the recorded signals in order to study the structural behaviour and to characterize the soil-structure interaction.Furthermore, we used normalized Short Time Fourier Transform (STFT) for the continuous monitoring of the structural response, in order to highlight possible frequency variations of the structural mode of vibration, and therefore of the structure's behaviour.To assess structural frequencies and to compare them with those evaluated by transfer functions, we used azimuth-dependent Fourier spectra. We also verified the suitability of the Horizontal-to-Vertical Spectral Ratio (HVSR) for estimating the dynamic characteristics of buildings when only single station seismic noise measurements are available.Regarding the structure-soil interaction, we identified the presence of a wave field back-radiated from the structure within the low amplitude seismic noise signal. In fact, in the free-field seismic noise recording spectra, peaks at frequencies consistent with those of the first two modes of the structure were recognized.

Evaluation and considerations about fundamental periods of damaged reinforced concrete buildings

“…The use of a fast procedure and a portable instrument allows studying a large number of buildings during an earthquake-related emergency. Gallipoli et al (2009Gallipoli et al ( , 2010 and Ditommaso et al (2010Ditommaso et al ( , 2012) have compared several techniques for structural dynamic identification: ambient noise vibrations are very useful for the characterization of the fundamental frequency and the related modal shape (if more than one station has been used). In this work the frequencies have been estimated using ambient noise recordings by means of a portable three-directional tromometer (Micromed Tromino).…”

Structural Health Monitoring Using Wireless Technologies: An Ambient Vibration Test on the Adolphe Bridge, Luxembourg City

“…The primary advantage of these approaches lies in the fact that no transient earthquake signals or even active excitation of the structure under investigation are required. Ditommaso et al [5] investigated the response characteristics of the Falkenhof Tower in Potsdam, Germany, using interferometric and time-frequency analysis techniques, using both ambient noise and records obtained from a near-by explosion. Prieto et al [6] performed a similar study using ambient noise records obtained in a 17-storey instrumented building at the University of California in Los Angeles, and Picozzi et al [7] tested the suitability of a system of low-cost wireless sensing units for real-time monitoring of large-scale infrastructure using the example of the Fatih Sultan Mehmet Suspension Bridge in Istanbul.…”

An effective approach for structural damage localization in flexural members based on generalized S-transform

“…Therefore, the FFT is not a proper tool for processing of nonstationary signals. Non-stationarity of the recorded signals is not just due to the damage in structures; even the non-stationarity of the input and the possible interaction with the ground or adjacent structures can show the ineffectiveness of classic techniques [5]. A large number of researchers have developed methods to overcome the above-mentioned problems of the FFT in processing of non-stationary signals.…”