236 A. Manuello et al. 30.4 AE Monitoring of the Double Girder Bridge Crane The monitoring results reported in the present study are devoted to the analysis of a steel structure consisted in a double girder bridge crane with a service load of 20 103 daN. The structure has over 30 years of service. The AE sensors were installed on one of the two beams of the bridge crane, a pair of sensors for each of the two ends, in correspondence of the supports, and the other four were positioned in correspondence of the middle part of the monitored element (see Fig. 30.4). The monitoring was carried out continuously for 120 h, from November 25 2013 to November 30 2013. The absence of AE signals during the moving of the structure was verified considering the absence of the service loads. From the analysis of the AE time series it is possible to correlate the AE activity with the most intense activity of the crane. Theˇt exponent indicated a substantial structural stability. At the same time the variability of the parameter b-value (between 3.8 and 2.8) is far from critical (bD1.5) or collapse (bD1) condition (see Fig. 30.5). By means of the localization procedure reported in the previous section triangulation of the AE signals was carried out to identify the AE sources. The localization results are shown in Fig. 30.6, showing an asymmetric distribution of the AE sources, localized prevalently towards a semi-beam of the crane. 30.5 Conclusions The paper shows the capability of a new AE data processing system based on wireless AE data transmission. The new AE equipment can be employed to realize contemporary long time monitoring of different civil structures and to perform AE signal analysis in real time. This system, cost efficient, easy to install, and adaptive to different types of concrete structural Fig. 30.4 Sensor positions on the double girder bridge crane (a). Application of the sensors in the middle of the beam (b) and in correspondence of the supports (c)
RkJQdWJsaXNoZXIy MTMzNzEzMQ==