30 Wireless Acoustic Emission Monitoring of Structural Behavior 237 Fig. 30.5 AE cumulated number (a), AE number per hour (b), Frequency range of AE signals (c), Time series of AE amplitudes (d), ˇt and b-value (e, f) Fig. 30.6 Scheme of the sensor positions and Localization of the AE sources and infrastructural networks, seems to be also very promising for seismic risk monitoring of civil structures and historical monuments. The AE cumulative number, theˇt exponent and theb-value have been computed in order to evaluate the damage evolution in a double girder bridge crane subjected to service loads. These analysis are the first parameter extrapolated from the AE data and represent damage indicators obtained in real time by the new AE equipment. After the AE data acquisition it is possible to perform the localization of the AE sources (micro-cracks). This analysis represents the second kind of data available by the AE monitoring. The position of damage, infact, is particularly useful in damage evaluation of concrete and masonry structures. In particular, the onset of AE signals from rock fracture is determined through the joint auto-regressive modelling of the noise and the signal, and the application of the Akaike Information Criterion (AIC) using the onset time as parameter. This so-called AICpicker is able to find accurately the onset of genuine signals against the background noise. The presented study suggests the use of AE measurements to enhance monitoring, especially applied to micro-seismicity with potential applications in earthquake forecasting. The monitoring system fine tuned could be used extending the acquisition to different kind of data in addition to AE signals. The data acquired from the sensor network will be sent electronically to a central server for real time monitoring of the condition of the buildings, by means of correlation algorithms applied to data from the different measured variables. This remote monitoring system will be maintained after the conclusion of the restoration work, allowing for detection and real time monitoring of possible structural deterioration processes of the buildings, thus constituting a useful tool for prevention of structural collapses. This monitoring system, if properly extended, may use the buildings as points of a monitoring network on the territory, useful for reducing the seismic hazard and securing entire metropolitan areas by monitoring the seismic activity.
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