Dynamic investigation of a suspension footbridge using accelerometers and microwave interferometer

The paper presents the main results of the serviceability assessment of a lively suspension footbridge. An ambient vibration test was firstly developed on July 2012 using conventional accelerometers with the objective of identifying the baseline dynamic characteristics of the structure; subsequently, groups of volunteers (up to 32 adults) simulated normal walking and running at different step rates along the deck and the human-induced vibrations were simultaneously measured by accelerometers and microwave interferometer. The deflection responses recorded by the microwave interferometer suggested the exceeding of comfort criteria threshold and this result was confirmed by the acceleration levels directly measured by accelerometers or derived from the (radar) displacement data. Furthermore, a second ambient vibration test was performed in Autumn 2012 using only the microwave interferometer: the natural frequencies of the footbridge generally exhibited not negligible variations, that were conceivably associated to the change of suspension forces induced by temperature, so that special care is suggested in the design of the devices aimed at mitigating the excess of human induced vibrations observed in the footbridge

Application of Microwave Remote Sensing to Dynamic Testing of Stay-Cables

Recent advances in radar techniques and systems have favoured the development of microwave interferometers, suitable for the non-contact vibration monitoring of large structures. The paper addresses the application of microwave remote sensing to the measurement of the vibration response in the stay-cables of cable-stayed bridges. The reliability and accuracy of the proposed technique were investigated by comparing the natural frequencies (and the cable tensions predicted from natural frequencies) identified from radar data and the corresponding quantities obtained using more conventional techniques. The investigation, carried out on the cables of two different cable-stayed bridges, clearly highlights: (a) the accuracy of the results provided by the microwave remote sensin

One-year dynamic monitoring of a masonry tower

The paper presents some results of the continuous dynamic monitoring program carried out on the tallest historic tower in Mantua, Italy. This project follows an extensive diagnostic investigation aimed at assessing the structural condition of the tower after the Italian earthquakes of May 2012. A simple dynamic monitoring system was permanently installed in the upper part of the building and automatic modal identification was performed. The results allow to evaluate the effects of changing temperature on automatically identified natural frequencies, to verify the practical feasibility of damage detection methods based on natural frequencies shifts and provide clear evidence of the possible key role of continuous dynamic monitoring in the preventive conservation of historic towers

Dynamic and seismic health monitoring of a historic masonry tower

The paper presents some results of the continuous dynamic/seismic monitoring program carried out on the tallest historic tower in Mantua, Italy. This project follows an extensive diagnostic investigation aimed at assessing the structural condition of the tower after the Italian earthquakes of May 2012. A simple dynamic monitoring system was installed in the tower to evaluate the dynamic response especially to the expected sequence of far-field earthquakes and to check the possible evolution of the natural frequencies; the response to ambient excitation has been continuously collected in 1-hour records since late December 2012. The paper summarizes the results of the continuous dynamic monitoring for a period of 8 months, highlighting the effect of temperature on automatically identified natural frequencies, the dynamic response to few seismic events and the key role of permanent dynamic monitoring in the diagnosis of the investigated historic building

One-year dynamic monitoring of a historic tower: damage detection under changing environment

The paper summarizes the conceptual development of a vibration-based strategy suitable to the structural health monitoring of ancient masonry towers and exemplifies its application in the continuous dynamic monitoring of the tallest historic tower in Mantua, Italy. The presented approach is based on the installation of low-cost monitoring systems (consisting of few accelerometers and temperature sensors) and on the combined use of automated operational modal analysis, regression models to mitigate the environmental effects on identified natural frequencies and multivariate statistical tools to detect the occurrence of abnormal structural changes. The application of the adopted strategy to 15 months of continuously collected experimental data: (1) highlighted the effect of temperature on the automatically identified natural frequencies; (2) demonstrated the practical feasibility of damage detection methods based on natural frequency shifts; (3) provided a clear evidence of the possible key role of continuous dynamic monitoring in the preventive conservation of historic towers

Pre-diagnostic prompt investigation and static monitoring of a historic bell-tower

An extensive research program is currently in progress to assess the structural condition of the bell-tower of the Church Santa Maria del Carrobiolo in Monza, Italy and to address the preservation of the historic building. The research program was consequent to the direct survey of the tower, carried out within a wide cataloguing activity of the main religious buildings in Monza and highlighting a weak structural layout of the bell-tower. The paper presents the main results of the investigation program performed to date and including: (a) documentary research, systematic visual inspection on site and experimental evaluation of the fundamental period of the tower, carried out using an industrially engineered microwave interferometer; (b) installation of a static monitoring system aimed at surveying the opening of the main cracks, possibly related to the recent construction of an underground car park in the close neighbourhood of the church; (c) dynamic tests in operational conditions, performed using conventional high-sensitivity accelerometers with the twofold objective of validating a FE model of the tower and implementing the installation of a continuous dynamic monitoring system

Unsupervised real‐time SHM technique based on novelty indexes

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Static and dynamic monitoring of a Cultural Heritage bell-tower in Monza, Italy

A recent survey carried on the historic complex of Santa Maria del Carrobiolo in Monza (Italy) highlighted that the two sides of the bell-tower are directly supported by the load-bearing walls of the apse and South aisle of the neighboring church. After the discovery of the weak structural arrangement of the building, static and dynamic monitoring systems were installed in the tower to address its preservation. After a brief description of the tower and the results of the preliminary survey, the paper presents selected results of the continuous dynamic monitoring as well as the evidences provided by the static monitoring

Dynamic assessment of the axial force in the tie-rods of the Milan Cathedral

The Milan Cathedral, constructed over a period of more than 400 years, is one of the few Gothic cathedrals where permanent metallic tie-rods are installed under all naves to support a portion of the lateral thrust exerted by vaults and arches. After the recent failure of one tie-rod, an extensive research program was carried out to characterize the metallic material and to evaluate the axial forces and the tensile stresses of the tie-rods through dynamic testing and system identification. After a description of the methodology adopted in the dynamic assessment of tie-rods in the Milan Cathedral, the paper presents the main results of the investigation, in terms of fundamental frequencies and axial forces in the tie-rods