Acoustic Emission Monitoring of the Turin Cathedral Bell Tower: Foreshock and Aftershock Discrimination

Historical churches, tall ancient masonry buildings, and bell towers are structures subjected to high risks due to their age, elevation, and small base-area-to-height ratio. In this paper, the results of an innovative monitoring technique for structural integrity assessment applied to a historical bell tower are reported. The emblematic case study of the monitoring of the Turin Cathedral bell tower (northwest Italy) is herein presented. First of all, the damage evolution in a portion of the structure localized in the lower levels of the tall masonry building is described by the evaluation of the cumulative number of acoustic emissions (AEs) and by different parameters able to predict the time dependence of the damage development, in addition to the 3D localization of the AE sources. The b-value analysis shows a decreasing trend down to values compatible with the growth of localized micro and macro-cracks in the portion of the structure close to the base of the tower. These results seem to be in good agreement with the static and dynamic analysis performed numerically by an accurate FEM (finite element model). Similar results were also obtained during the application of the AE monitoring to the wooden frame sustaining the bells in the tower cell. Finally, a statistical analysis based on the average values of the b-value are carried out at the scale of the monument and at the seismic regional scale. In particular, according to recent studies, a comparison between the b-value obtained by AE signal analysis and the regional activity is proposed in order to correlate the AE detected on the structure to the seismic activity, discriminating foreshock, and aftershock intervals in the analyzed time series

Acoustic emission wireless monitoring of structures and infrastructure

The damage assessment of buildings is currently made visually. The few non-visual methodologies make use of wired devices, which are expensive, vulnerable, and time consuming to install. Systems based on wireless transmission should be cost efficient, easy to install, and adaptive to different types of structures and infrastructures. The Acoustic Emission (AE) technique is an innovative monitoring method useful to investigate the damage in large structures. It has the potential to detect damage, as well as to evaluate the evolution and the position of cracks. This paper shows the capability of a new data processing system based on a wireless AE equipment, very useful to long term monitoring of concrete and masonry structures. To this purpose, computer-based procedures, including an improved AE source location based on the Akaike algorithm, are implemented. These procedures are performed by automatic AE data processing and are used to evaluate the AE results in notched concrete beams subjected to three point bending loading conditions up to the final failure. In this case, the final output of the code returns a complete description of damage pattern and evolution of the monitored structure. In the most critical cases, or in some cases requiring long in situ observation periods, the AE monitoring method is fine tuned for a telematic procedure of processing AE data clouds to increase the safety of structures and infrastructural networks. Finally, the proposed AE monitoring system could be used to determine the seismic risk of civil constructions and monuments subjected to earthquakes

Shell and spatial structures: Between new developments and historical aspects

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Acoustic emission of the SyracuseAthena temple: timescale invariancefrom microcracking to earthquake

We show the results of acoustic-emission (AE) monitoring of the Cathedral of Syracuse in Sicily (Southern Italy), built around the surviving elements of a Doric temple dedicated to Athena from the 5th century BC. We wired up a single pillar of the 2500-year-old cathedral for four months and then compared the AE data with earthquake records, observing a time correlation between the AE bursts and the sequence of nearby earthquakes and a similar scaling for the related magnitude distributions. We found that the distribution of times between events —whether earthquakes or acoustic emissions— fell onto the same curve, over a wide range of timescales and energies, when scaled appropriately. A similar ‘universal scaling law’ has been shown for collections of earthquakes of a range of sizes in different regions, so the new results appear to extend the law to the much smaller energy scales of a single pillar. These pieces of evidence suggest a correlation between the aging process and the local seismic activity, and that more careful monitoring of the cathedral is warranted

Acoustic emission wireless monitoring of structures and infrastructure

The damage assessment of buildings is currently made visually. The few non-visual methodologies make use of wired devices, which are expensive, vulnerable, and time consuming to install. Systems based on wireless transmission should be cost efficient, easy to install, and adaptive to different types of structures and infrastructures. The Acoustic Emission (AE) technique is an innovative monitoring method useful to investigate the damage in large structures. It has the potential to detect damage, as well as to evaluate the evolution and the position of cracks. This paper shows the capability of a new data processing system based on a wireless AE equipment, very useful to long term monitoring of concrete and masonry structures. To this purpose, computer-based procedures, including an improved AE source location based on the Akaike algorithm, are implemented. These procedures are performed by automatic AE data processing and are used to evaluate the AE results in notched concrete beams subjected to three point bending loading conditions up to the final failure. In this case, the final output of the code returns a complete description of damage pattern and evolution of the monitored structure. In the most critical cases, or in some cases requiring long in situ observation periods, the AE monitoring method is fine tuned for a telematic procedure of processing AE data clouds to increase the safety of structures and infrastructural networks. Finally, the proposed AE monitoring system could be used to determine the seismic risk of civil constructions and monuments subjected to earthquakes

Signal frequency distribution and natural-time analyses from acoustic emission monitoring of an arched structure in the Castle of Racconigi

The stability of an arch as a structural element in the thermal bath of King Charles Albert (Carlo Alberto) in the Royal Castle of Racconigi (on the UNESCO World Heritage List since 1997) was assessed by the acoustic emission (AE) monitoring technique with application of classical inversion methods to recorded AE data. First, damage source location by means of triangulation techniques and signal frequency analysis were carried out. Then, the recently introduced method of natural-time analysis was preliminarily applied to the AE time series in order to reveal a possible entrance point to a critical state of the monitored structural element. Finally, possible influence of the local seismic and microseismic activity on the stability of the monitored structure was investigated. The criterion for selecting relevant earthquakes was based on the estimation of the size of earthquake preparation zones. The presented results suggest the use of the AE technique as a tool for detecting both ongoing structural damage processes and microseismic activity during preparation stages of seismic events

Reinforced masonry with FRP and structural mortar: durability evaluation by AE technique

The aim of this work is to analyse and compare the shear resistance after long-term and environmental actions on brickwork structures reinforced by innovative or traditional techniques. To this end laboratory tests were carried out at the Non-Destructive Testing Labora-tory of the Politecnico di Torino. In addition, the Acoustic Emission technique was employed to assess the damage localization, and the mechanical properties decay in order to evaluate the ef-fectiveness of these rehabilitation methodologies