# Dynamic Identification on an Irregular Structure
## 3 Experimental Campaign
As shown in Figure 7 the accelerometers were positioned on two opposite vertices of the two polygons, when possible (Second and Roof floor), or only on one vertex (Raised and First floor); in fact, their positioning was conditioned by the accessibility of the individual rooms where the four vertices fell. Along the vertical direction the vertices of the polygons have been chosen aligned because this position favors to identify the behavior of the structure. Figure 7: View of the directions of acquisition of the accelerometers installed at the Raised floor (**a**), the First floor (**b**), the Second floor (**c**) and the Roof floor (**d**). The testing setup was composed by n. 28 accelerometers PCB 393B31 (sensitivity 10 V/g, frequency range 0.1 to 200 Hz), n. 11 three-channel Dynamic Signal Acquisition Module (12.8 KS/channel, 30 V, capable of measuring signals from IEPE and non-IEPE sensors), n. 3 chassis CompactDAQ 9178 and RG58 coaxial cables with impedance 50 \(\Omega\). Each CompactDAQ 9178 chassis is connected to a modem by means of an ethernet cable and connected to the others by means of a synchronization cable. The data acquired by the control units are therefore sent via wireless connection from the model to the computer on which the data acquisition software is installed. Specifically, the data acquisition software used is National Instrument's LabVIEW (Laboratory Virtual Instrumentation Engineering Workbench), which allows customizing the way the measurement data is acquired, displayed, and managed. The selection of the points to be monitored was made by considering dividing the plan into the polygons characterized by rigid plan behavior, thus the sensors have been installed at the vertices of these polygons in order to be able to evaluate the displacements of each part. Each point was monitored along two orthogonal directions; thus, to assure this condition, two sensors have been installed in each point on two different faces of an aluminum cube (see Figure 8). A total number of 14 points have been monitored subdivided as follows: three points at the Raised floor (Figure 7a) and First floor (Figure 7b), four points at the Second (Figure 7c) and Roof floor (Figure 7d). The n. 3 CompactDAQ have been installed to acquire the signals of the accelerometers; in Figure 7 each DAQ was indicated by a different color and the sensors have been drawn by utilizing the color of the DAQ to which they are connected to. Three different tests have been conducted, each one of about 10 min and with an acquisition frequency of 1024 Hz. A total of 28 ICP accelerometers perfectly synchronised and perfectly aligned to the orthogonal x, y directions (horizontal xy plane) in the 14 selected measurement points have been used. The very high sampling rate available for each accelerometer (1024 Hz) was fully utilised both in the acquisition phase and in the subsequent processing phase. Considering that each test was carried out with a continuous acquisition in environmental  
Figure 8: View of the sensors installed in one of the monitored points. conditions of 10 min, for each accelerometer, 614,400 samples were acquired for each test, a total of 17,203,200 acceleration data. All the acquired data were used in the identification phase for each test. The acquisition system has already been widely used previously by the authors for the dynamic monitoring of structures as follows: a preliminary calibration phase was performed in the laboratory and a subsequent phase in situ provided the choice of the measurement points and the arrangement of the accelerometers which are screwed onto blocks, suitably made to maintain the orthogonality of the measurements and, in turn, connected with specific glues to the points of the structure; all these operations are widely described in previous experiences and carried out with standard methods that do not require further investigation.