Wireless and stand-alone measurement system for dynamic identification of structures

This paper contains a study about a wireless Bluetooth measurement system useful in order to control the accelerations on great dimensions structures. The structure on which they have been carried out is a steel structure with rectangular plan. On the upper level there has been installed a vibrodine for generating a sinusoidal force for dynamic characterization of the structure. The realized measurement system utilizes a datalogger and some accelerometer/ they communicate among themselves through wireless Bluetooth protocol, which allows to cover distances up to 100 m. The datalogger is a common PC equipped with a module for Bluetooth communication. The accelerometers are constituted by: 1) a triaxial acceleration sensor, with adjustable range among the following values [1.5, 2, 4, 6] g; 2) a gyroscope with input range of 150 degrees/second; 3) a microcontroller, with analogue to digital converter with maximum sampling frequency of 610 Hz, which samples the signals and manages the device; 4) a class 1 Bluetooth module which allows the communication over universal platform; 5) a 860 mAh battery. The datalogger is equipped with a software developed in Lab View environment; it is able to simultaneously acquire acceleration's samples from every accelerometer and to obtain in real time plots of accelerations, speeds and displacements and to save the samples in binary files for successive processing. The experimentation has been finalized to the calibration of the numerical model to guarantee the structure functionality and also to study the structure behaviour under dynamic actions generated by wind. This experimental activity concurred also to discover modal shape not easily recognizable also using a corrected dynamics analysis.