Vibration Analyses of a Gantry Structure by Mobile Phone Digital Image Correlation and Interferometric Radar

Francesco Mugnai,Paolo Mazzanti,Grazia Tucci,Antonio Cosentino

doi:10.3390/geomatics2010002

Francesco Mugnai, Paolo Mazzanti + Show 2 more

Open Access

https://doi.org/10.3390/geomatics2010002

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Journal: Geomatics	Publication Date: Dec 27, 2021
Citations: 2	License type: CC BY 4.0

Affiliation: University of Florence, Sapienza University of Rome

Abstract

The study presents results from applying the Real Aperture Radar interferometry technique and Digital Image Correlation through a mobile phone camera to identify static and dynamic deformations of a gantry during surveying operations on the Michelangelo’s David at the Galleria dell’Accademia di Firenze Museum in Florence. The statue has considerable size and reaches an elevation of more than seven meters on its pedestal. An ad-hoc gantry was designed and deployed, given the cramped operating area around the statue. The scanner had a stability control system that forbid surveying in instrument movements. However, considering the unicity of the survey and its rare occurrence, the previous survey had been carried out in the year 2000; verifying stability and recording deformations is a crucial task, and necessary for validation. As the gantry does not have an on-board stability sensor, and considering the hi-survey accuracy requested, a redundant, contactless, remote monitoring system of the gantry and the statue stability was chosen to guarantee the maximum freedom of movement around the David to avoid any interference during scanning operations. Thanks to the TInRAR technique, the gantry and the statue were monitored with an accuracy of 0.01 mm. At the same time, a Digital Image Correlation analysis was performed on the gantry, which can be considered a Multi-Degree-Of-Freedom (MDOF) system, to accurately calculate the vibration frequency and amplitude. A comparison between TInRAR and DIC results reported substantial accordance in detecting gantry’s oscillating frequencies; a predominant oscillation frequency of 1.33 Hz was identified on the gantry structure by TinSAR and DIC analysis.

Highlights

Structural monitoring systems are widely adopted to estimate the behavior of structures under ambient and forced vibrations in a laboratory or field environment and used to monitor structures under other excitations, such as earthquakes, traffic, gusts, or live loads
From the various studies [12,14] it was observed that this TInRAR remote sensing technique for Structural Health Monitoring” (SHM) applications could provide results comparable to those obtained through other conventional ‘contact’ monitoring techniques, such as velocimeter or accelerometer, or sensor networks installed on structures [2,15,16,17]
As first suggested by Patsias and Staszewskiy [27,28], each pixel of a digital video or photo taken on a structure can represent a candidate virtual visual sensor (VVS) that can be used for SHM purposes

Summary

Introduction

Structural monitoring systems are widely adopted to estimate the behavior of structures under ambient and forced vibrations in a laboratory or field environment and used to monitor structures under other excitations, such as earthquakes, traffic, gusts, or live loads. The basic concept is that small changes in the intensity value of a monitored pixel with fixed coordinates caused by the vibration of structures can be captured by employing techniques, such as the Fast Fourier Transform (FFT) [18]. In this approach, as first suggested by Patsias and Staszewskiy [27,28], each pixel of a digital video or photo taken on a structure can represent a candidate virtual visual sensor (VVS) that can be used for SHM purposes.

Total Surface

Parameter Value

Nominal Displacement