Nicola Cavalagli

Vibration-based structural health monitoring of a historic bell-tower using output-only measurements and multivariate statistical analysis:

This article presents the development and the results of 1 year of implementation of a simple vibration-based structural health monitoring system for preventive conservation and condition-based maintenance of an Italian monumental masonry bell-tower. The system is based on the data recorded by a small number of high-sensitivity accelerometers, on remote automated frequency tracking and on a multivariate statistical analysis criterion for damage detection, combining data regression, principal component analysis, and novelty analysis. The analysis of monitoring data highlights the main characteristics of the response of the tower to wind, swinging bells, and low-return period earthquakes. Despite the low levels of vibration in operational conditions, the system is seen able to track the time evolution of five natural frequencies of the structure and successfully use such information for detecting anomalous deviations from normal conditions. More in general, the presented results show a promise toward a more widespread use of low-cost vibration-based monitoring systems for cultural heritage preservation.

Dome of the Basilica of Santa Maria Degli Angeli in Assisi: Static and Dynamic Assessment

This study presents the results of the static and dynamic assessment of the dome of the Basilica of Santa Maria degli Angeli in Assisi, designed by Galeazzo Alessi. The first section is devoted to an overview of the masonry domes designed by the Italian architect and focuses on the structural solutions adopted in the several cases described to better understand Alessi’s designing skills. In the second part, the drum-dome system is analyzed in order to attain a structural assessment. The static assessment is performed by means of limit analysis and finite element model approaches with non-linear mechanical behavior. The obtained results are consistent with the detected crack pattern and confirm the suitability of the reinforcement steel rings applied to the drum. The seismic assessment has been performed by response spectrum analysis. Due to the lack of specific information, a probabilistic approach for the material mechanical properties was used. The results obtained highlight an adequate seismic response of the structure that can be attributed to the dynamic properties of the slender drum-dome system. This finding justifies the good performance of the structure during the seismic events of 1832 and 1997.

Structural Investigation of 18th-Century Ogival Masonry Domes: From Carlo Fontana to Bernardo Vittone

In this study a structural investigation on the ogival masonry domes is performed with particular attention to the significant debate between mathematicians and architects mainly of the French and Italian schools that characterized the 18th century. In this period, analytical approaches to investigate the static of dome structures were developed concurrently for the affirmation of the proportional methods, as reported in several architectural treatises in which graphical constructions for the design of masonry domes can be found. It is well known that Carlo Fontana, in 1694, was the first to show in detail the geometrical rules for the design of a masonry dome. Later, in 1760, the Italian architect Bernardo Antonio Vittone proposed some variations to the rules written by Fontana in order to increase the height of the dome and the slope of the meridian section at the intersection with the lantern. In this study, Vittone’s dome has been analyzed and compared with Fontana’s dome by means of an analytical approach that also considers the influence of the lantern at the top. The obtained results confirm that Vittone’s rules lead not only to architectural, but also structural improvements.

Earthquake-Induced Damage Detection in a Monumental Masonry Bell-Tower Using Long-Term Dynamic Monitoring Data

ABSTRACT This work investigates the use of an advanced long-term vibration-based structural health monitoring tool to automatically detect earthquake-induced damages in heritage structures. Damage produced in a monumental bell-tower at increasing values of the Peak Ground Acceleration (PGA) of the seismic input is predicted by incremental nonlinear dynamic analysis, using a Finite Element model calibrated on the basis of experimentally identified natural modes. Then, predicted damage effects are artificially introduced in the monitoring data to check for their detectability. The results demonstrate that a very small damage, associated to a low intensity and low return period earthquake, is clearly detected by the monitoring system.

Laser doppler and radar interferometer for contactless measurements on unaccessible tie-rods on monumental buildings: Santa Maria della Consolazione Temple in Todi

Non-contact measurements can be effectively used in civil engineering to assess the variation of structural performance with time. In the last decades this approach has received considerable interests from researchers working in the field of structural health monitoring (SHM). Indeed, non-contact measurements are very attractive because it is possible to perform non intrusive and non destructive investigations even being at a significant distance from the targets. Within this context, contactless measurements of the tie-rod vibrations in the Santa Maria della Consolazione Temple in Todi (Italy) are presented in this paper. In particular, laser vibrometer and radar interferometer measurements are used to estimate natural frequencies and mode shapes. This information is crucial to obtain the tensile axial force in the tie-rods, which can be used as an indicator of structural integrity or possible failure. Furthermore, a novel approach is proposed where drones (Unmanned Aerial Vehicles) can be successfully used to improve the effectiveness and the accuracy of the experimental activities.

In Situ Shear Tests on Masonry Panels Strengthened with Fiber-Reinforced Mortar Repointing

In this paper the effect of joints structural repointing on single-wythe brickwork masonry using a fiber-reinforced mortar is investigated. Changes in shear strength are evaluated by in-situ tests carried out both on unreinforced and reinforced masonry specimens. The masonry joint shear strength, according to the standard ASTM C 1513, gives local information, while diagonal compression tests provides information on the global masonry shear response. The comparison highlights a good performance in both local and global masonry response, where the shear strength increases.

DYNAMIC TESTING AND MONITORING OF HISTORIC TOWERS FOR SEISMIC DAMAGE DETECTION

Structural health monitoring (SHM) systems represent an acknowledged low-invasiveness and low-cost solution enabling real time condition assessment of civil structures, providing useful information for preventive conservation and maintenance activities. The various documented successful applications of SHM systems to bridges and large infrastructural systems has recently led many researchers to investigate their effectiveness in the case of monumental and historical buildings, often vulnerable to both anthropogenic a natural (e.g. seismic) hazards. The countries in the Mediterranean Basin are especially committed to this kind of research, being, at the same time, rich of built cultural heritage and highly exposed to seismic and other natural hazards. Among the various types of historic buildings, Italian Cities are especially characterized by an extensive presence of bell and civic masonry towers, which also deserve a special attention because of their slenderness, making them suitably monitored via vibration-based systems, and because of their seismic vulnerability. Framing in the afore-depicted scenario, the authors have started in the last years a research activity on vibration-based permanent SHM of slender historic towers, finalized at the implementation of new approaches for the optimal management of the limited available budgets for conservation and restoration activities. In the present paper the results concerning this activity are presented with specific reference to two study cases in the city of Perugia, Italy: the bell tower of the Basilica of San Pietro and the civic tower called “Torre degli Sciri”. The two considered monuments present completely different characteristics and complexities from both structural and architectural points of view, making them worth interesting investigating as typological benchmarks. The work discusses both ambient vibration testing and permanent mon-itoring applications, including considerations regarding the adopted sensing hardware. The feasibility of a rapid post-earthquake damage detection via SHM is finally explored with reference to the study case of the San Pietro bell tower, with particular attention to the recent seismic events. 2564 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 2564-2577

STRUCTURAL MONITORING OF MONUMENTAL BUILDINGS: THE BASILICA OF SANTA MARIA DEGLI ANGELI IN ASSISI (ITALY)

Abstract. The preservation of architectural heritage and monumental structures is an important challenge of the scientific research, especially for the countries where cultural heritage is of primary concern and, at the same time, there are significant risk factors due to natural hazards as earthquakes. In this perspective, structural health monitoring systems can improve the protection of structures by providing real-time diagnostic data together with suitable procedures, which are able to identify possible occurring problems. In this work the first results given by a monitoring system placed in the Basilica of Santa Maria degli Angeli in Assisi will be presented. Data recorded by nine linear variable displacement transducers (LVDTs) are shown together with power spectral densities of acceleration time histories measured during ambient vibration tests. The spectral analysis results are compared with the natural frequencies given by a numerical model of the Basilica structural system.