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

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

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

Continuous dynamic monitoring of the Milan Cathedral: influence of environmental changes on the dynamic characteristics

The Milan Cathedral is the most iconic symbol of Milan and is world-wide known for being one of the largest heritage monuments ever built. Since October 2018, a large monitoring system is active in the monument with the main objective of assisting the condition-based structural maintenance of the historic church through the continuous interrogation of sensors installed in the structure and the extraction from measured data of features which are representative of the current state of structural health. Different sensing technologies were adopted in order to allow appropriate tracking of different long-term structural behaviour. The dynamic monitoring of the horizontal response of selected piers and along the main spire is complemented by the measurement of the quasi-static tilt of the same sub-structures, whereas the static monitoring of strain in selected tie-rods gives a direct evaluation of the structural condition of those elements (as the tensile force in the tension bars was previously evaluated). Since both the long-term static behaviour and the time evolution of dynamic signatures of historic masonry structures are expected to be sensitive to environmental changes, the indoor and outdoor environmental parameters are extensively measured as well. The paper is mainly aimed at presenting selected results from the dynamic monitoring of the Milan Cathedral. After a concise description of the historic church and of the dynamic monitoring system, the paper focuses on the dynamic characteristics of the cathedral, their evolution during 3 years of monitoring and the lessons learned in view of the structural health monitoring of the monument

Serviceability assessment of a suspension foorbridge before and after the implementation of tuned mass dampers

The paper summarizes the main results of the dynamic tests performed to assess the vibration serviceability of a lively pedestrian bridge. Firstly, the dynamic characteristics of the suspension footbridge were extensively investigated before its opening. Operational modal testing (with the excitation being mainly provided by micro-tremors and wind) allowed to identify 10 vibration modes in the frequency range 0-5 Hz: the frequency of the fundamental mode was close to 1.0 Hz and five modes turned out to fall in the frequency range 2-3 Hz. Subsequently, groups of volunteers simulated normal walking and running at different step rates along the deck. The human-induced vibrations were measured and the results clearly indicated that the maximum vertical acceleration significantly exceeds the comfort criteria threshold suggested in guidelines and codes of practice, so that a control system with 5 tuned mass dampers (TMDs) was designed. After the installation of the TMDs, the dynamic tests were repeated at different air temperature and clearly revealed only a partial success of the vibration mitigation due to the high sensitivity of the structure (and its natural frequencies) to the environmental effects

Continuous monitoring of a challenging heritage tower in Monza, Italy

A recent survey of the historic complex of â\u80\u9cSanta Maria del Carrobioloâ\u80\u9d 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 paperâ\u80\u94after a brief description of the tower and a summary of selected evidences provided by on-site survey, historic research and static monitoringâ\u80\u94focuses 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

ONE YEAR STATIC MONITORING OF THE MILAN CATHEDRAL

The paper focuses on the long-term monitoring of the Milan Cathedral. After a concise historic background on the monument and the description of the sensing devices installed in the church, selected results obtained during the first year of static monitoring are summarized as well as the lessons learned in view of the Structural Health Monitoring (SHM) of the Cathedral. In more details, the time evolution of different static features (i.e. strain of metallic tie-rods and tilt of columns) is presented, along with the correlation between those features and the environmental parameters and the possible minimization/removal of the environmental effects with SHM purposes

Ambient vibration tests on New Zealand unreinforced masonry churches using low cost sensors

Churches are an important part of New Zealand's architectural heritage, and the extensive damage observed in stone and clay brick unreinforced masonry churches after the 2010-2011 Canterbury earthquakes has highlighted the need to appropriately describe their dynamic characteristics. Dealing with historical structures, characterized by a high level of uncertainty affecting both material properties and structural schemes, and given the paramount need of non-destructive investigation techniques, ambient vibration tests can be considered an effective tool. A test campaign was conducted on two churches located in Auckland and deemed to be representative of the New Zealand church portfolio. The structures were instrumented with low-cost tri-axial standalone accelerometer sensors based on Micro Elec-tro-Mechanical Systems (MEMS) technology. Despite such instrumentation being commonly used on more flexible structures and/or under higher service loads (such as the normal traffic on bridges), this technology potentially represents an affordable solution to provide information about the fundamental period of vibration of macro-elements of churches and bell-towers. The advantages and limitations of the adopted sensing technology, when applied to historic buildings exhibiting low response to ambient excitation, are discussed in the paper, based on the analysis of data collected

P3P: a software suite for autonomous SHM of bridge networks

This paper presents the development of a new software code for the fully autonomous management of permanent integrated Structural Health Monitoring (SHM) systems installed in highway bridge structures. The code was developed within the framework of a research project funded by Anas S.p.A., the largest public infrastructure manager in Italy. The software program includes all the necessary steps to conduct SHM within the statistical pattern recognition paradigm, including automated dynamic identification, modal tracking, filtering of environmental effects, and damage detection through novelty analysis. Additionally, the software suite includes specific modules for processing and analysis of seismic events and structural reliability analysis of bridges, as well as specific functionalities for span-wise identification of long multi-span bridges. Moreover, a novel automated density-based tracking algorithm is developed. The potential of P3P is illustrated through two real application case studies: (i) a long multi-span bridge, the Trigno V Bridge in Italy; and (ii) the Z-24 Bridge benchmark. This work demonstrates the effectiveness of the developed code for handling large monitoring databases within the framework of SHM as a statistical pattern recognition, and currently P3P is in phase of being applied by Anas S.p.A for the management of a large number of bridges of the Italian roadway system