Complementarietà delle indagini termografiche e georadar nella diagnostica degli edifici

Le indagini non distruttive sugli edifici stanno avendo un progressivo sviluppo nell’ingegneria civile. Le tecniche di geofisica applicata trovano in questo settore numerose applicazioni e stimoli per nuove ricerche. I restauratori e gli ingegneri civili, dall’applicazione di queste tecnologie richiedono informazioni sulla geometria degli elementi non visibili, sul loro stato di ammaloramento e sulla matrice che compone i materiali dell’edificio. Una tale quantità di informazioni eterogenee richiede l’utilizzo di più sistemi basati su principi fisici di funzionamento diversi. In questo lavoro ci si è occupati dell’analisi delle potenzialità di individuazione e ricostruzione delle geometrie degli elementi non visibili di un edificio. Le tecnologie considerate sono state la Termografia (attiva e passiva) e il Georadar, metodologie differenti nei principi fisici di funzionamento, nelle possibilità operative e investigative. È presentato il caso di studio di una campagna di misure sperimentali Georadar e Termografica su di un edificio storico per verificare la complementarietà delle due metodologie

Prompt structural assessment of historic towers

The paper presents the diagnostic procedure and the results of the investigation program performed on the bell- tower of the Church Santa Maria del Carrobiolo in Monza, Italy. Preliminary documentary research and systematic visual inspection on site highlighted a weak structural layout of the bell-tower; furthermore, the recent construction of an underground car park in the close vicinity of the church has triggered the movement of several cracks. During the visual inspection, a prompt dynamic test was also carried out using an industrially engineered microwave interferometer. Subsequently, ambient vibration tests were performed with the twofold objective of validating a FE model of the tower and implementing the installation of a continuous dynamic monitoring system

Long-term dynamic monitoring of the historic “San Michele” iron bridge (1889)

The San Michele bridge is an iron arch bridge that crosses the Adda river about 50 km far from Milan. The bridge, built in 1889, is the most important monument of XIX century iron architecture in Italy and is still used as a combined road and railway bridge. In order to assess the structural condition of the bridge, ambient vibration tests were performed in 2009 and suggested the opportunity of installing a permanent dynamic monitoring system with Structural Health Monitoring purpose. Hence, a continuous monitoring system was designed and it is now active on the bridge since late November 2011. The paper, after a brief summary of the experimental studies developed since 2009, describes the monitoring system and the software developed in LabVIEW for processing the collected data. Subsequently, the tracking of natural frequencies automatically identified until the beginning of September 2012 is presented and the effects of environmental and operational conditions on the dynamic response of the bridge are investigated

Post-earthquake diagnostic investigation of a historic masonry tower

The paper describes the methodology applied to assess the state of preservation of the tallest historictower in Mantua, the Gabbia Tower, after the Italian earthquakes of May 2012. An extensive experi-mental programme − including geometric survey, visual inspections, ambient vibration tests, sonic andflat-jack tests − has been planned and carried out to support the future preservation actions of the tower.The paper focuses especially on the outcomes of on-site survey and dynamic tests and highlights theeffectiveness of integrating the information obtained from these tests to assess the structural conditionand seismic vulnerability of the tower. The adopted experimental methodology, generally suitable as aprompt diagnostic procedure, successfully detected the local vulnerabilities as well as the overall stateof preservation of the tower and addressed the subsequent monitoring phase

Dynamic testing of masonry towers using the microwave interferometry

Microwave remote sensing is the most recent experimental methodology suitable to the non-contact measurement of deflections on large structures, in static or dynamic conditions. After a brief description of the radar measurement system, the paper addresses the application of microwave remote sensing in ambient vibration testing of two historic masonry towers

Continuous dynamic monitoring of a centenary iron bridge for structural modification assessment

A multi-channel continuous dynamic monitoring system has been installed in a centenary iron arch bridge on late November 2011. The historic infrastructure, completed in 1889 and crossing the Adda river about 50 km far from Milan, is the most important monument of XIX century iron architecture in Italy and is still used as roadway and railway bridge. The monitoring project follows a series of preliminary ambient vibration tests carried out on the bridge since June 2009. The paper describes the bridge structure and its dynamic characteristics identified from the experimental studies developed since 2009, the installed monitoring system and the software developed in LabVIEW for automatically processing the collected data. Subsequently, the tracking of automatically identified natural frequencies over a period of about 18 months is presented and discussed, highlighting the effects of environmental and operational conditions on the bridge dynamic characteristics as well as the detection of structural changes, mainly based on natural frequencies shifts

Monitoring and FE modeling of a historic iron bridge

The paper summarizes some results of the investigation performed since 2009 on the San Michele bridge (1889), one of the most important monuments of XIX century iron heritage. The diagnostic campaign aimed at the assessing the structural state of preservation includes preliminary dynamic testing, monitoring and FE model development and calibration. Within the ongoing Structural Health Monitoring of the bridge, the dependence of the dynamic characteristics (i.e. natural frequencies and mode shapes) on several parameters such as temperature and amplitude of the excitation, is addressed and discussed in the paper

Structural Identification of a Masonry Tower Based on Operational Modal Analysis

A wide program of structural assessment has been carried out by Politecnico di Milano on the historic bell tower of the church Chiesa Collegiata in Arcisate (Varese, northern Italy). Within this context, the first part of the article summarizes the results obtained from the application of the stochastic subspace identification method to ambient response data collected in two dynamic tests, carried out in June 2007 and June 2008. Next presented is the vibration-based methodology developed for the calibration of a three-dimensional finite element model of the tower, consisting in the successive application of systematic manual tuning, sensitivity analysis, and simple system identification algorithm

Post-earthquake continuous dynamic monitoring of the Gabbia Tower in Mantua, Italy

The Gabbia Tower, about 54.0 m high and dating back to the XIII century, is the tallest tower in Mantua, overlooking the historic centre listed within the UNESCO Heritage. After the seismic sequence of May 2012 in Italy, an extensive research program was carried out to assess the structural condition of the tower. The post-earthquake investigation (including direct survey, historic and documentary research, testing of materials and ambient vibration tests) highlighted the poor state of preservation of the upper part of the building and suggested the installation of a dynamic monitoring system to evaluate the response of the tower to the expected sequence of far-field earthquakes and check the possible evolution of the structural behavior. After a brief description of the tower and the post-earthquake survey, the paper presents the results of the continuous dynamic monitoring for a period of 8 months, highlighting the effect of temperature on automatically identified natural frequencies, the practical feasibility of damage detection methods based on natural frequencies shifts and the key role of permanent dynamic monitoring in the diagnosis of the investigated historic building