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The research implements a procedure based on (H)BIM (Historic Building Information Modelling) operational practices for the structural assessment of heritage slender structures. The application of HBIM creates a digital model integrated with all the information for the structural modelling and for the intervention design. The activity starts from detailed on site surveys, inspections, documentary research, geomatics surveys, dynamic testing aimed to the development and calibration of a FE model. The proposed methodology is applied to the Arengario, the 13th-century Town Hall of Monza, representing the main symbol of the city.

This paper focuses on the reliability of a synergistic procedure, involving dynamic tests complemented by documentary and architectural research, for the structural assessment of heritage towers. The reliability of the presented method is exemplified in a relevant case study, the Zuccaro's Tower in Mantua. As is known, historic buildings require addressed procedures in order to consider past building transformation and eventual damage/decay, which can affect the masonry properties and, more generally, the structural behavior. The proposed investigation procedure is based on multidisciplinary information (i.e., merging data) from historical and document studies, direct inspections, surveys of geometry and front surfaces, and dynamic tests in operational conditions. The processed information allowed the development and the calibration of a simplified numerical model, useful in driving the seismic/structural assessment of the tower. The results of past investigations, found during the archival research, contributed to the structural evaluation. This paper describes the main research outcomes and the model tuning with a special focus on the key role of the synergy between the applied methods for the assessment of a historic building. [ABSTRACT FROM AUTHOR]

Correct approaches to the assessment of historic structures involve the collection of data related to materials, building technology, eventual damage and decay, and transformation that has occurred over time. The procedure proposed by the authors is based on multidisciplinary research, merging data ranging from documentary and archive research to structural modeling. In the developed procedure, the minimization of the costs and timing of the structural assessment were the main requirements. The procedure, implemented on the Arengario, the 13th-century Town Hall of Monza, focuses on the key role of historic and documentary research in order to highlight the difference in the building technology. The overall research program involves the following steps: (i) historical analysis and documentary research; (ii) visual inspections, geometric survey, and decay/damage identification and mapping; and (iii) dynamic testing and modal identification, with these steps driving the choices involved in the subsequent step: (iv) FE modeling and updating. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents and discusses the results of investigations carried out by the authors on two castles that are considered as case histories within a project financed by the [...]

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.

The results of the long-term vibration monitoring program, carried out on the bell-tower of Santa Maria del Carrobiolo in Monza (Italy), are reported in the paper. The dynamic monitoring was motivated by the weak structural layout of the historic building, with two fronts of the tower being supported by the load-bearing structures of the apse and South aisle of the adjacent church. Furthermore, closely spaced modes with similar mode shapes were clearly identified from ambient vibration tests, hence, the modal parameters of the bell-tower significantly differ from those obtained in past experimental studies of similar masonry structures. The continuous dynamic monitoring was mainly aimed at enhancing the knowledge of the historic structure, checking the possible evolution of the key resonant frequencies and assessing the effects of changing temperature on the dynamic characteristics of the bell-tower. The main results of the dynamic monitoring for a period of two years highlight distinctive behavior of the bell-tower, such as the frequency veering exhibited by the lower modes with increased temperature. Subsequently, in order to mitigate the effects of the environmental factors on resonant frequencies, the application of the multiple linear regression (MLR) and the principal component analysis (PCA) tools have been investigated. [ABSTRACT FROM AUTHOR]

A recent survey of the historic complex of “Santa Maria del Carrobiolo” in Monza (Italy) highlighted that two sides of the bell-tower are directly supported by the load-bearing walls of the apse and South aisle of the neighbouring church. After the discovery of the weak structural arrangement of the building, a network of 10 displacement transducers, integrated by five temperature sensors, was installed in the tower to check the opening variation of the main cracks. Subsequently, ambient vibration tests were performed and closely spaced modes with similar mode shapes were clearly identified: since the dynamic characteristics of the tower are quite different from those obtained in past experimental studies of similar structures and conceivably related to the construction sequence, a simple dynamic monitoring system was installed in the tower to complete the health monitoring aimed at the preservation of the historic structure. The paper—after a brief description of the tower and a summary of selected evidences provided by on-site survey, historic research and static monitoring—focuses on the dynamic characteristics identified in the preliminary ambient vibration tests and the main results of 1-year dynamic monitoring. In order to assess the effects of changing temperature on the natural frequencies of the investigated tower, especially in view of the removal of those effects needed for an effective performance assessment, simple correlation studies between modal frequencies and temperature are presented and discussed. [ABSTRACT FROM AUTHOR]

The paper summarizes the results obtained during the continuous dynamic monitoring of two iconic Cultural Heritage towers -the Gabbia tower in Mantua and the San Pietro bell-tower in Perugia. The two towers, exhibiting different architectural and structural characteristics, were monitored over a similar time period (of about 2 years) by Politecnico di Milano and University of Perugia, respectively, and similar methodologies of automated operational modal analysis and structural health monitoring were adopted by the two Research Teams. During the monitoring, both the towers underwent far-field seismic events which caused slight structural damage. In both case studies, the limited number of accelerometers installed in the towers allows the tracking of automatically identified modal frequencies and to distinguish between environmental and damage effects on the natural frequencies. Furthermore, the occurrence of structural anomalies corresponding to small drops in frequencies is confirmed through multivariate statistical analysis, based on principal component analysis and novelty detection. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The paper describes the strategy adopted to assess the structural condition of the tallest historic tower in Mantua (Italy) after the Italian seismic sequence of May-June 2012 and exemplifies the application of health monitoring using (automated) operational modal analysis. The post-earthquake survey (including extensive visual inspection, historic and documentary research, non-destructive (ND) material testing, and ambient vibration tests) highlighted the poor state of preservation of the upper part of the tower; subsequently, a dynamic monitoring system (consisting of a few accelerometers and one temperature sensor) was installed in the building to address the preservation of the historic structure, and automated modal identification was continuously performed. Despite the low levels of vibration that existed in operational conditions, the analysis of data collected over a period of about 15 months allowed to assess and model the effects of changing temperature on modal frequencies and to detect the occurrence of abnormal behavior and damage under the changing environment. The monitoring results demonstrate the potential key role of vibration-based structural health monitoring, implemented through low-cost hardware solutions and appropriate software tools, in the preventive conservation and the condition-based maintenance of historic towers. [ABSTRACT FROM AUTHOR]

The paper describes the methodology applied to assess the state of preservation of the tallest historic tower in Mantua, the Gabbia Tower, after the Italian earthquakes of May 2012. An extensive experimental programme − including geometric survey, visual inspections, ambient vibration tests, sonic and flat-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 the effectiveness of integrating the information obtained from these tests to assess the structural condition and seismic vulnerability of the tower. The adopted experimental methodology, generally suitable as a prompt diagnostic procedure, successfully detected the local vulnerabilities as well as the overall state of preservation of the tower and addressed the subsequent monitoring phase. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

Abstract: The paper focuses on the dynamic tests of two historic structures, performed in operational conditions at different levels of ambient excitation. The tests were aimed at checking the invariance of the dynamic characteristics (i.e. natural frequencies and mode shapes) with increasing excitation amplitude. A masonry bell tower, dating back to the XVI century, is firstly considered and the modal parameters of key vibration modes were identified from the data collected in two ambient vibration tests: in the first test, the excitation was only provided by micro-tremors and wind, whereas in the second test a higher level of excitation was induced by swinging of bells. The second structure is a well-known iron arch bridge, erected in 1889 and still used as a combined road and rail bridge. Within the dynamic tests performed on the historic infrastructure since June 2009 to address a Structural Health Monitoring program, the bridge response at selected points was continuously recorded for several hours, in order to check the variation of the dynamic characteristics under different traffic conditions. [Copyright &y& Elsevier]

The long-term research experience of the authors has highlighted the importance of gaining knowledge of the building through experimental investigation. Recently the authors intensively studied the Syracuse Cathedral (Sicily, Italy) to evaluate the structural state of the preservation of the pillars. The Cathedral of Syracuse was built in different phases on an ancient Greek temple from the fifth century bc and modified throughout later centuries. The pillars of the central nave, obtained by cutting the temple cell walls, show a complex situation of damage and repairs. An investigation program (including radar, sonic, and ultrasonic tests, for example) has been recently planned, aimed to design the preservation and restoration actions. An accurate geometric survey of the surface problems and defects allowed the localization of the most damaged area, suggesting the need for further control by non-destructive testing (NDT). The results obtained from this survey were compared with the results of the other type of tests, and the elaborated data will be used to implement an analytical model for the study of the seismic vulnerability. The preliminary results of the experimental investigation carried out by the authors are presented in this article. [ABSTRACT FROM AUTHOR]