Page History: Test and Validation
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Page Revision: 2010/09/24 15:40
A single degree of freedom structure represented by an inverted pendulum is one of the simplest examples used by the civil engineers to explain the fundamentals of the dynamics of structures. In this work, this structure was also used as a tool to evaluate and understand the behaviour of the developed prototype for operational modal analysis of civil engineering structures. The laboratory specimen consists in an inverted wooden pendulum with 1.70 m height built specially for testing purposes in the civil engineering laboratory at the University of Minho. The pendulum was designed in such a way that its dynamic properties replicates the properties of the Mogadouro´s Clock Tower, an old masonry tower in the northern part of Portugal
link for the Luis Ramos’ studied that led to the development of the pendulum.
For comparison purposes, both WSN platforms (full COTS solutions based on MICA2 platforms and MTS400 sensor board, and the project prototype system) were evaluated considering as references conventional wired based systems which consist in high sensitivity piezoelectric accelerometers model PCB 393B12
link as well as the NI-USB9233
link as data acquisition board.
The initial tests were meant to observe the performance of the COTS technology on WSN platforms for dynamic monitoring studies. With this purpose, the accuracy of the time series recordings of these platforms (MICA2 + MTS400 sensor board) was evaluated using only one of the conventional accelerometers and placed at the top of the Pendulum.
The results of the first test indicated the good performance of the commercial WSN platforms for measuring high amplitude vibrations. As it was expected, for signals with amplitudes below 20 mg, the WSN platforms recorded only noise (it is even feasible to observe the digitalizing lines) due to the low resolution of the micro-accelerometers and the ADCs embedded. However, it is important to state that in SHM studies of civil engineering structures, vibrations with amplitudes below 2 mg are commonly found. Moderate differences (less than 5%) were found in the frequencies detected with both systems (wired and COTS WSN) as well as meaningless results for the mode shape detection task due to the lack of the implementation of synchronization algorithms in the commercial WSN platforms.