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

Zinc Supported by Nitrogen-Rich Ligands: Applications Towards Catalytic Hydrosilylation And Modeling Zinc Enzymes

In chapter 1, I discuss how ligand architecture in tripodal nitrogen-rich ligands can drastically affect the structure of zinc complexes featuring these ligands. The synthesis and characterization of zinc tris(1-methylimidazol-2-ylthio)methyl ([Titmᴹᵉ]) and tris(1-Pribenzimidazol-2-ylthio)methyl ([Titmⁱᴾʳᵇᵉⁿᶻᵒ]) complexes is presented. The ligand in [Titmᴹᵉ]Zn complexes binds the metal to form carbatrane structures that exhibit unusually long and flexible Zn–C bonds. The bonding between the zinc and the carbon in these complexes can therefore be more accurately described as a zwitterionic interaction between a carbanion and a zinc cation. Density functional theory calculations demonstrate that the energy profile for the Zn–C bond is shallow, such that large variations of the Zn–C distance result in very little change in the energy of the complex. The benzannulated ligand [Titmⁱᴾʳᵇᵉⁿᶻᵒ] allows access to a rare monomeric zinc hydride species [κ³-Titmⁱᴾʳᵇᵉⁿᶻᵒ]ZnH that can react with either CO₂ to produce a zinc formate, or B(C₆F₅)₃ to form the ion pair [κ⁴-Titmⁱᴾʳᵇᵉⁿᶻᵒ]ZnHB(C₆F₅)₃. The coordination chemistry of the [Titmⁱᴾʳᵇᵉⁿᶻᵒ] ligand also extends to the other metals of group 12. In chapter 2, I report the use of the [Titmᴹᵉ] and [Titmⁱᴾʳᵇᵉⁿᶻᵒ] zinc complexes presented in chapter 1 as biomimetic models for zinc enzymes. First, [Titmᴹᵉ] zinc complexes present structural similarities with the active site of carbonic anhydrase, and can be used to study the binding of carbonic anhydrase inhibitors to the enzyme active site. Then, [κ⁴-Titmⁱᴾʳᵇᵉⁿᶻᵒ]ZnX (X = MeB(C₆F₅)₃, BPh₄) complexes and their interactions with ligands of relevance towards antibiotic resistance is reported. The non coordinating nature of the anions in [κ⁴-Titmⁱᴾʳᵇᵉⁿᶻᵒ]ZnX (X = MeB(C₆F₅)₃, BPh₄) lead to the formation of a Lewis acidic zinc cationic center, which can be coordinated by an additional ligand of biological interest. The binding of simple β-lactams to the [κ⁴-Titmⁱᴾʳᵇᵉⁿᶻᵒ]ZnX complexes can be probed using X-ray diffraction and Nuclear Magnetic Resonance (NMR) spectroscopy, thereby providing a way to model the binding of antibiotics to the active site of the metallo-β-lactamases enzymes responsible for broad antibiotic resistance. The binding of β-lactams can be compared to larger ring size lactams and linear amides. [κ⁴-Titmⁱᴾʳᵇᵉⁿᶻᵒ]ZnX (X = MeB(C₆F₅)₃, BPh₄) also allows for the study of the binding of potential metallo-β-lactamases inhibitors, such as, for example, glycinamide, picolinamide, and piperazine-2,3-dione. Binding studies between [κ⁴-Titmⁱᴾʳᵇᵉⁿᶻᵒ]ZnX and substrates bearing structural similarities to antibiotics reveal secondary interactions involving peripheral functional groups the cationic zinc center in [κ⁴-Titmⁱᴾʳᵇᵉⁿᶻᵒ]ZnX. These studies provide guidelines to modify existing antibiotics, in order to decrease their sensitivity to metallo-β-lactamases. In chapter 3, I explore the reactivity of previously characterized tris(2-pyridylthio)methyl [Tptm] zinc complexes. First, an improved synthesis of [κ⁴-Tptm]ZnF using Me₃SnF as the fluorinating agent is reported. The fluorine atom in [κ⁴-Tptm]ZnF acts as a Lewis base, as illustrated by its reaction with B(C₆F₅)₃ to form [κ⁴-Tptm]ZnFB(C₆F₅)₃, in which the fluorine is transferred to the borane group. The fluoride ligand in [κ⁴-Tptm]ZnF also acts as a hydrogen bond and halogen bond acceptor and is capable of forming adducts with H₂O, indole, and iodopentafluorobenzene. [κ⁴-Tptm]ZnF undergoes metathesis with Ph₃CCl to form Ph₃CF, thereby providing a rare example of C–F bond formation promoted by a zinc complex. Then, [κ³-Tptm]ZnH is used as a catalyst for the hydrosilylation of aldehydes and ketones using phenylsilane to produce tris alkoxysilane products. The catalyst is very active with aldehydes, and shows slower reactivity towards dialkyl ketones. The reaction proceeds via insertion of the carbonyl group in the Zn–H bond to form a zinc alkoxide, which then undergoes metathesis with the silane to generate the desired product and regenerate the zinc hydride species. The complicated NMR spectroscopic features of the products resulting from the hydrosilylation of prochiral ketones are explained by the presence of different diastereomers. Finally, we report that [κ³-Tptm]ZnH is a catalyst for the hydrosilylation of silylformates to methoxy silanes with (EtO)₃SiH, (MeO)₃SiH and κ⁴-N(CH₂CH₂O)₃SiOMe. We show that CO₂ can be reduced to methoxy silane species in a one pot reaction using (MeO)₃SiH and catalytic amounts of [κ³-Tptm]ZnH. In chapter 4, I report the synthesis and characterization of a silicon based analogue of [Titmⁱᴾʳᵇᵉⁿᶻᵒ], namely the tris(1-Pribenzimidazol-2-yldimethylsilyl)methyl [Tismⁱᴾʳᵇᵉⁿᶻᵒ] ligand. The ligand possesses unique structural features, due to the proximity between the dimethylsilyl groups and the methyl carbanion. The formation of [κ⁴-Tismⁱᴾʳᵇᵉⁿᶻᵒ]Li proceeds via the doubly base stabilized silene intermediate [κ³-C(SiMe₂benzimidⁱᴾʳ)₂]SiMe₂. [κ⁴-Tismⁱᴾʳᵇᵉⁿᶻᵒ]Li can be used as a precursor for copper and nickel [Tism^iPr,benzo] and [C₃-Tismⁱᴾʳᵇᵉⁿᶻᵒ] complexes, where [C3-Tismⁱᴾʳᵇᵉⁿᶻᵒ] represents the isomerized tris carbene version of [Tismⁱᴾʳᵇᵉⁿᶻᵒ]. [κ³-C(SiMe₂benzimid^ⁱᴾʳ)₂]SiMe₂ reacts with ZnMe₂ to produce [κ³-C(SiMe₃)(SiMe₂benzimidⁱᴾʳ)₂]ZnMe, which can be transformed to the phenoxide compound. This compound acts as a catalyst for the hydrosilylation of CO₂ to silyl formates and methoxy silanes. [κ³-C(SiMe₂benzimidⁱᴾʳ)₂]SiMe₂ itself reacts with CO₂ to produce an unusual β-lactone

Dynamic monitoring of ancient masonry towers: Environmental effects on natural frequencies

Masonry towers are very common Cultural Heritage buildings in Italy, where churches and bell-towers were built even in smaller towns and a large number of defensive towers dates back to Middle Age. Since ancient towers exhibit a cantilever-like dynamic behavior and are usually sensitive to ambient excitation, such as micro-tremors and wind, a successful dynamic monitoring of these structures can be obtained by permanently installing a few high-sensitivity accelerometers in the upper part of the building. Hence, the idea of performing cost-effective vibration-based Structural Health Monitoring (SHM) of historic towers has been taking shape recently. On the other hand, the use of a limited number of sensors and automated operational modal analysis in SHM often implies the choice of resonant frequencies as damage sensitive features, although modal frequencies are also affected by factors other than structural changes in a way that is likely more significant than variations induced by a small damage. In order to highlight the possible effects of changing temperature on the dynamic characteristics of masonry towers, especially in view of the removal of those effects needed for an effective performance assessment, the paper focuses on selected results obtained by continuously monitoring the dynamic response of three historic towers in Italy

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 monitoring of the Milan Cathedral: dynamic characteristics and vibration-based SHM

The traditional collaboration between Politecnico di Milano and Veneranda Fabbrica del Duomo di Milano—the historic institution established by Gian Galeazzo Visconti in 1387 and having in charge all operational aspects related to the Milan Cathedral since more than 600 years—recently focused on the design and installation of a structural monitoring system, with the 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. The new monitoring system of the Milan Cathedral includes different types of measurements and sensors: quasi-static acquisition of strain in selected tie-rods and biaxial tilt of selected piers and the main spire, monitoring of inner and outer environmental parameters and dynamic measurement of the velocity response at the top of 14 piers and at 3 levels of the main spire. After a concise description of the historic church and of the monitoring system, the paper focuses on the dynamic characteristics of the Milan Cathedral, their evolution during the first months of monitoring (since October 16th, 2018) and the lessons learned in view of the structural health monitoring of the monument. The presented results from the vibration monitoring highlight that: (a) 8 global modes of vibration are automatically detected in the frequency range 1.0–5.0 Hz; (b) the resonant frequencies exhibit a distinctive trend of variation, which is mainly driven by temperature; (c) the mode shapes of the cathedral do not show appreciable fluctuations associated with the environmental effects

Estimating the Tensile Force in Ancient Metallic Tie-Rods from Vibration Tests

One of the distinctive characteristics of the Milan Cathedral is the presence of iron ties under the vaults of all 5 naves: those tension bars date back to the age of construction and still have an important role in supporting the lateral thrust exerted by vaults and arches.During the maintenance interventions preceding EXPO 2015, almost all the tie-rods of the cathedral underwent visual inspection, geometric characterization and hammer tests to evaluate their dynamic characteristics. After a brief summary of the experimental procedures, the paper focuses on presenting and exemplifying the structural identification approach adopted in the vibration-based assessment of the tensile force in the metallic ties. The presented procedure differs from the one proposed by Tullini and Laudiero (2008) since: (a) the Young's modulus of the metallic material is assumed to be unknown and (b) the resonant frequencies of higher modes are used to solve the inverse problem.The application of the proposed procedure is mainly exemplified with reference to the tension bars exhibiting the higher stress level (larger than 100 MPa) as those elements are now permanently instrumented with vibrating wire extensometers. Selected results from the long-term monitoring of the tie-rods are briefly discussed as well

Your Next Big Idea

As you start to brainstorm that next research project, make sure you’re using all the data available to help you put the pieces together, particularly if you work in highly interdisciplinary areas. This session will include doing a literature search on your topic to determine what’s already been published – not only in your domain of expertise but also in less familiar fields. Analyze results to find out who the prominent researchers, institutions and funders are in your field

Environmental effects on the dynamic characteristics of a historic cathedral

The maintenance and preservation of the Milan Cathedral is traditionally performed through well-established and time-scheduled programs of visual inspection and architectural restoration of surfaces, decorations, and statues in Candoglia marble. On the other hand, the structural condition assessment and preservation turns out to be a challenging task due to the dimensions and complexity of the building, the usual uncertainties on the material properties and also the difficulty in inspecting several structural elements. Therefore, a structural monitoring system was recently designed and installed in the Milan Cathedral to assist the condition-based structural maintenance of the monument. The monitoring system includes different sensing technologies to allow appropriate tracking of different long-term structural behavior. The dynamic monitoring of the horizontal response of selected piers is complemented by the static monitoring of the tilt of the same piers and of the strain in selected tie-rods. In addition, the indoor and outdoor environmental parameters are extensively measured as well. After a concise historic background on the historic monument and the description of the dynamic monitoring system installed in the Milan Cathedral, the paper focuses on the dynamic characteristics of the monument, that were identified in the first hours of continuous monitoring, Subsequently, the results of the first year of dynamic monitoring are presented and discussed, with special attention being given to the influence of environmental parameters on the variations observed in the resonant frequencies and mode shapes. In more details, the presented results highlight that: (a) 8 global vibration modes are automatically detected in the frequency range 1.0-5.0 Hz; (b) the variations observed in the resonant frequencies are mainly driven by temperature, with the effect of thermal changes being very peculiar; (c) the mode shapes and the related mode complexity do not exhibit appreciable fluctuations associated to the environmental changes, so that an appropriate strategy of SHM should be based also on the time invariance of those parameters