Masonry Bell Tower Research Articles

Static and Seismic Safety of the Inclined Tower of Portogruaro: A Preliminary Numerical Approach

Masonry towers are peculiar structures with complex structural behavior despite biased conclusions deriving from their geometrical regularity and simplicity. Their geometrical features and the epistemic uncertainty that masonry material bears strongly influence their static and seismic behavior. This paper investigates a remarkable and representative case study. The bell tower of Portogruaro (Italy) is a 57 m high tall construction, built in the XII-th century, and has a notable inclination. The Italian Guideline for the safety assessment of masonry towers is a key focus in this paper, highlighting the pros and cons of different suggested approaches. Some relevant proposals are presented in this paper in order to address the seismic safety assessment of masonry bell towers. The findings show that very slender structures do not meet the guidelines recommendations due to limitations in their current stress state. In addition, in similar cases, the recommended values for the mechanical properties of masonry material led to predicting non-withstanding structural behavior, questioning the correct choice of the adapted material properties. Advanced pushover analysis has been conducted in order to investigate the results of the simplified approach in terms of failure patterns and seismic safety estimation. The simulations are implemented for four different hypothetical scenarios of the existing masonry mechanical properties. The results obtained for the case study tower reflect a different perspective in the seismic assessment of masonry towers when specific approaches are defined. The preliminary results on the safety of Portogruaro Tower show a significant variability of seismic safety based on the adopted scenario, highlighting the necessity to pay attention to the preservation state of the present case and of similar ones.

Correction: Observed damage and simplified risk assessment of Italian masonry bell towers struck by past seismic events

Correction: Observed damage and simplified risk assessment of Italian masonry bell towers struck by past seismic events

Observed damage and simplified risk assessment of Italian masonry bell towers struck by past seismic events

Observed damage and simplified risk assessment of Italian masonry bell towers struck by past seismic events

Modal and Structural Identification of Historic Bell Tower in Čuntić, Croatia Using Ambient Vibration Testing

In this study, modal and structural identification of a historic masonry bell tower in Čuntići, Croatia, damaged during the recent Petrinja earthquake, was performed. The results of the ambient vibration tests (AVT) and operational modal analysis (OMA) were used to update the finite element numerical model of the bell tower. Three modes were experimentally determined: the first two were bending modes (f1 = 4.395 Hz and f2 = 4.639 Hz), and the third was a torsional mode (f3 = 10.303 Hz). The experimentally determined and the originally calculated (preliminary NM) modal shapes agreed well, but in terms of modal frequencies, the correlation was poor. After model updating, some structural parameters were identified, and a reliable finite element numerical model was established. The proposed method can provide a reliable evaluation of the structural parameters of historic masonry buildings.

Engineering Geological and Geophysical Studies Supporting Finite Element Analysis of Historical Buildings after Dynamic Identification

Resonance frequencies of a masonry bell tower were estimated by means of ambient noise measurements and compared with those computed by using fixed base, Winkler, and FE numerical, including subsoil. Given the geological complexity that characterizes the subsurface of the analyzed area, despite the presence of massive volcanic outcrops near the bell tower, we carried out a geophysical characterization of the subsoil by using active and passive seismic surveys. These surveys have identified a soft substrate underneath the construction; for this reason, the dynamic identification of the tower was performed, including the interaction with the soil. The resonance frequencies of the masonry bell tower computed by the models are very similar to those obtained using ambient noise. Results suggest that building resonance frequencies, estimated by ambient noise surveys, can be used because of their reliability especially when quick analyses are required at historical buildings located in seismically active areas needing plan actions to reduce their vulnerability. Moreover, such analyses, being performed on samplings acquired within the structure, allow for estimating its dynamic response, taking into account the effect of subsurface characteristics as well.

Wavelet level decomposition of the seismic response of a historic masonry bell tower with and without simulated structural damage

Historical buildings are of foremost importance due to their unique and irreplaceable value. However, their ageing structure and materials make them particularly vulnerable to structural damage. This may result in catastrophic failure under strong motions, which are unfortunately not uncommon in seismic areas such as Italy. This numerical study discusses the application of Wavelet Level Decomposition (WLD) to the seismic response of such historical structures. The simulated data are obtained from a calibrated Finite Element (FE) model of the Santa Maria and San Giovenale Cathedral bell tower in Fossano (Northern Italy). This structure suffered major structural damage during an earthquake in 1887; it then underwent several interventions, the last one being in 2012. It is also currently scheduled for further reinforcement works in the near future. The FE analyses consider a set of realistic earthquake inputs in accordance with the seismic hazard zone of Fossano, with and without damage (modelled as a stiffness reduction in the façades, considering several possible crack patterns). The results show the potential for WLD-based retrospective analysis after seismic events on recorded signals.

Surrogate-based bayesian model updating of a historical masonry tower

This paper presents the surrogate-based Bayesian model updating of a historical masonry bell tower. The finite element model of the structure is updated on the basis of the modal properties experimentally identified thanks to a vibration test. In a general context, model updating results are highly affected by several uncertainties, regarding both the experimental measures and the model. Stochastic approaches to model updating, as the one based on Bayes’ theorem, enable to quantify the uncertainties associated to the updated parameters and, consequently, to increase the reliability of the identification. The major drawback of Bayesian model updating is the high computational effort requested to compute the posterior distribution of parameters. For this reason, the paper proposes to integrate the classical procedure with a surrogate model. A Gaussian surrogate is employed for the approximation of the posterior distribution of parameters and the performances of the proposed method are compared to those of an Bayesian numerical method proposed in literature.

A mechanics-based model for simplified seismic vulnerability assessment of masonry bell towers

The safeguard of historical heritage cannot disregard a rational assessment of the seismic vulnerability of the assets, especially in areas as Italy where high exposure and hazard may lead to significant risk. In this context, while established empirical methods based on observed damage after earthquakes are available for some constructional typologies as churches and palaces, large-scale approaches for masonry bell towers aimed at defining a vulnerability ranking for prioritisation of intervention are still missing or not sufficiently validated.In this paper, a novel simplified vulnerability model is formulated through sensitivity-informed parameter reduction of a more detailed mechanics-based assessment methodology. The framework is based on (a) a parametric representation of the bell tower, (b) a mechanical model providing a measure of collapse, (c) a vulnerability definition based on the measure of collapse. The variation ranges of the input parameters are calibrated against the results of the surveys carried out in the historical centre of Naples. A global sensitivity analysis is then used to identify the most important parameters governing the vulnerability of the structure and remove the least influential parameters. Vulnerability models based on different amount of input data are finally proposed, and their accuracy is assessed comparatively with the original mechanical model. The results show that good accuracy can be obtained by using six geometrical and typological parameters, while further increase in the quality of the prediction may be achieved with the introduction of additional information regarding materials and constructional features, which can only be acquired by means of more detailed surveys on-site.

Radar Interferometric Experimental Reconstruction of Three-Dimensional Displacement Vectors and Mode Shapes for Masonry Constructions

Abstract Radar interferometry is an innovative measurement technique capable of remotely measuring vibrations in terms of displacement history. It apparently allows overcoming some major drawbacks of the plodding and time-consuming conventional accelerometric experimental setup for vibration testing. Indeed, radar interferometry does not require any access to the structure; moreover, its use is simpler and faster. Therefore, this technique appears very appealing for ambient vibration testing on structures, and in particular on architectural heritage masonry constructions. However, radar interferometry is still affected by some relevant limitations, that currently outweigh the advantages. One of the most important limitations is that displacements are measured only along the line-of-sight; therefore, it is not possible to determine the whole three-dimensional displacement vector for moving structural points and, consequently, to reconstruct three-dimensional mode shapes of structures, whose knowledge is crucial for characterizing the dynamic behavior of structures and for detecting eventual damages. In this paper, a theoretical and experimental approach for reconstructing both three-dimensional displacement vectors and mode shapes of masonry constructions is proposed. This approach is based on the simultaneous use of two synchronized radar interferometers, and on the application of a theoretical model assuming a specific kinematical constraint, which is generally plausible in the case of masonry constructions. The proposed approach has been validated through in-situ experimental tests on a masonry bell tower.

Dynamic behavior of a masonry bell tower subjected to actions caused by bell swinging

Seismic response of masonry towers has been widely studied, whereas research on their behavior under other dynamic forces is not common. The aim was to study the dynamic effects of bell swinging on a masonry tower, evaluating the response through different approaches. For this purpose, the south tower of the National Palace of Mafra was adopted due to its slenderness and its four swinging bells located at 49 m height. Dynamic identification tests allowed to determine the tower’s dynamic properties aimed at calibrating a numerical model. Frequency analyses assessed possible resonance effects by comparing the frequencies of the excitations with those of the tower. Nonlinear dynamic analyses evaluated the response in terms of displacements and cracking, while nonlinear static analyses determined damage patterns assuming different load combinations. Variations of structural stiffness and intensity of the forces were also studied. The results demonstrated that the tower, subjected to bells action, remains within the elastic range with a high safety level. Moreover, crack patterns correspond to local damage, which do not compromise the stability of the structure. Finally, parametric analysis allowed to obtain equivalent static load factors for bells of the Spanish system.

Seismic vulnerability assessment and earthquake response of slender historical masonry bell towers in South-East Lombardia

Masonry bell towers represent a large portion of the Italian cultural heritage and are highly vulnerable to seismic actions mainly due to their relevant slenderness, as also observed in recent seismic events. The present study investigates the seismic vulnerability and earthquake response of five slender historical masonry bell towers, which are located in South-East Lombardia (Northern Italy), through a preliminary simplified procedure suggested by the Italian Code and advanced numerical simulations. To thoroughly study the seismic response of the bell towers, detailed three-dimensional FE models with a damage plasticity constitutive law for masonry are developed and non-linear dynamic analyses are performed using different accelerograms. The results of the non-linear dynamic analyses show that the geometrical features and the main vibration properties of the bell towers turn out to be the main parameters influencing the seismic performance of such a construction typology. Moreover, it can be noted a clear influence of the accelerograms characteristics on both the energy dissipated by tensile damage and the maximum normalized displacements of the bell towers. On the other hand, the structural geometrical characteristics play a very important role in terms of damage distribution among the different parts of the bell towers. In addition, the main limitations of the simplified approach suggested by the Italian Code for the seismic assessment of the bell towers under study are highlighted through a comparison with the results obtained from non-linear dynamic analyses. The main outcomes presented in this study may also represent a useful insight to better understand the earthquake response and seismic vulnerability of similar masonry bell towers located in the same region, providing valuable information that can be directly used in seismic risk assessment at regional scale.

Seismic Upgrading of a Historical Masonry Bell Tower through an Internal Dissipative Steel Structure

Masonry towers are part of a valuable architectural heritage characterizing the landscape of many historical areas. These towers are vulnerable structures that are prone to earthquake damage. Hence, the design of effective seismic upgrading interventions is an important task for preserving such architectural forms for future generations. In view of that, the objective of this study is to contribute a possible addition to the portfolio of available approaches for seismic upgrading of masonry towers. This goal was pursued by exploring an innovative structural solution that does not alter the external appearance of the tower and its static scheme under gravity loads, yet is able to increase its capacity to withstand seismic actions through added damping. Specifically, the proposed solution consists of a steel structure internal to the masonry tower that incorporates fluid viscous dampers. In order to evaluate its potentialities, a real case study was taken as a testbed structure, historic analysis as well as geometric and architectural surveys were undertaken, an initial design for the upgrading was made, and numerical simulations were performed. The obtained results, although preliminary, highlight the potentialities of the proposed structural solution for the seismic upgrading of masonry towers and might open the way to future developments and applications.

Seismic Capacity Estimation of a Masonry Bell-Tower with Verticality Imperfection Detected by a Drone-Assisted Survey

Masonry towers are considered an important part of cultural heritage due to their architectural and historical value. From a structural perspective these kind of buildings are considered slender elements, the same as a cantilever beam. In real cases it is not easy to model with high accuracy these heritage constructions, since the geometry and mechanical properties of the constituent materials are not adequately known. On the other hand, a deep knowledge of the structural and seismic vulnerability of the masonry towers is needed in order to preserve and retrofit, when necessary, their architectural and cultural value. In the present research an exhaustive study is presented, as it regards the assessment of the seismic vulnerability of a heritage masonry bell-tower, built in the 14th century. An innovative protocol of structural survey followed, and it is proposed herein. The geometry of the tower was easily obtained by digital photogrammetry assisted by a drone. The geometrical model was easily converted into a digitalized input, that was introduced into a finite element method (FEM)-based code. The 3D model was used for linear static, linear dynamic and nonlinear static (pushover) structural analyses. The vulnerability of the masonry tower was assessed and at least one kinematic was found to be not verified.

Model Updating of Historical Belfries Based on Oma Identification Techniques

ABSTRACT Central Italy Earthquakes occurred in 2016 pointed out once more the vulnerability of Cultural Heritage (CH), especially for what concerns bell-towers since they tend to get dramatically damaged due to their considerable slenderness and deterioration, endangering their surroundings and making their preservation fundamental. This work presents the results of the study carried out on four different isolated masonry bell towers, located in Ferrara province (Italy); the parameters of the materials were deduced by calibrating Finite Element Models (FEMs) using the data collected during an investigation campaign conducted with a wired accelerometric sensor system, since it was not possible to apply destructive methodologies. Dynamic data were extracted through the application of two Operational Modal Analysis (OMA) identification techniques: the Enhanced Frequency Domain Decomposition (EFDD) and the Stochastic Subspace Identification (SSI) methodology. Particular attention was devoted to the use of MAC matrix in the validation of the mode shapes results.

Advanced numerical analyses by the Non‐Smooth Contact Dynamics method of an ancient masonry bell tower

Advanced numerical analyses were carried out in order to assess the nonlinear dynamical behaviour of the bell tower of Pomposa Abbey in Codigoro, in the province of Ferrara (Italy), by means of the Non‐Smooth Contact Dynamics (NSCD) method. The main purpose of the work is to investigate the capacity of the main mechanical parameter used in the analyses, namely, the friction coefficient, to have effects on the mechanical response of ancient masonry structures undergoing seismic actions. Therefore, the tower was modelled following the discrete element method (DEM) and assembling the masonry texture as rigid bodies tied by frictional joints. Thus a discontinuous approach was used to assess the dynamic properties and the vulnerability of the masonry structure, through large deformations regulated by the Signorini's law, concerning the impenetrability between the rigid bodies; and by the Coulomb's law, regarding the dry‐friction model. Afterward, different values were assigned to the friction coefficient of the models, and a variety of real seismic shocks have been applied in the nonlinear analyses. Finally, it is possible to see different failure mechanisms resulting for each friction value and types of dynamic actions used, as expected.

Advanced Seismic Assessment of Four Masonry Bell Towers in Italy after Operational Modal Analysis (OMA) Identification

ABSTRACT The paper presents an advanced seismic assessment of four masonry bell towers located in Northern Italy based on detailed 3D FE models on which elastic parameters were previously identified by operational modal analysis. The numerical assessment includes a preliminary identification of the elastic moduli of the different volumes of each tower made by means of a fast-micro-GA approach. After proper identification of the main four eigenfrequencies, non-linear static (pushover) and full non-linear dynamic analyses are performed adopting a material model for masonry which is characterized by softening and two distinct damage parameters in both tension and compression. The results obtained with non-linear static and non-linear dynamic analyses in all the simulations performed exhibit a satisfactory match, suggesting similar conclusions in terms of general dynamic response and seismic vulnerability of the towers.

Dynamic monitoring and evaluation of bell ringing effects for the structural assessment of a masonry bell tower

The paper presents a rational procedure for the structural assessment of bell towers with respect to the dynamic actions induced by the bell ringing, based on structural monitoring and data processing. This methodology is tested on the bell tower of Saint Prospero (Reggio Emilia, Northern Italy), a masonry tower of great historical interest. The procedure includes an accurate geometrical survey for a deep knowledge of the structural geometry, which is the base for the structural modelling. A finite element model of the tower is calibrated with respect to the modal properties evaluated from the structural response measured in operational conditions. The structural response of the tower was also measured during a famous cultural event held in the city centre of Reggio Emilia, when skilled bell ringers played traditional melodies. The tower displacements are evaluated applying a double integration technique and a detrending procedure based on the empirical mode decomposition to the acquired accelerations. To simulate the structural response to the bell ringing, the tower and the bell are modelled as a single degree of freedom system and an unforced and undamped simple pendulum, respectively. For safety assessment purposes, the structural response of the tower is evaluated considering different oscillation angles in order to identify the one causing the maximum displacement. Finally, the stress pattern of the masonry caused by the bell-induced displacement is estimated thanks to the calibrated finite element model of the tower. Results show that the bell ringing causes a stress pattern lower than the allowable masonry strength for the serviceability conditions.

Effectiveness of different base isolation systems for seismic protection: Numerical insights into an existing masonry bell tower

Recent earthquakes in Italy have emphasized the high seismic vulnerability of historical masonry constructions and the need of effective retrofitting interventions. This paper investigates the possibility of improving the seismic performance of a historical masonry bell tower using different types of commercial isolators: High Damping Rubber Bearing (HDRB), Lead Rubber Bearing (LRB) and Friction Pendulum System (FPS) Isolator. Detailed three-dimensional (3D) finite element (FE) models are created to characterize the behavior of the three types of isolators. Then, an Abaqus User Element (UEL) is used to represent the 3D behavior of the isolators for global seismic analyses of isolated structures. The results of cyclic shear analyses show that the proposed UEL model can accurately predict the behavior obtained through detailed 3D FE models. Non-linear dynamic analyses are performed to investigate the seismic response of the historical masonry bell tower in the original and base-isolated configurations subjected to moderate-to-high seismic actions: moreover, the effects of near fault earthquakes are analyzed. The results obtained from the numerical simulations show that the HDRBs do not ensure an adequate seismic protection of the masonry bell tower in terms of damage patterns and top displacements. On the other hand, the LRBs and FPS isolators are very effective in reducing the earthquake effects on the masonry tower: residual displacements are negligible and the isolator displacements are limited. In case of near fault earthquakes, an isolation system with higher damping and larger dimension is required to reduce the drifts of the tower and to accommodate the large displacements of the isolators.

Seismic Vulnerability Analysis and Retrofitting of the SS. Rosario Church Bell Tower in Finale Emilia (Modena, Italy)

The Italian territory is rich of constructions belonging to the architectural heritage which deserve to be protected against earthquakes. In seismic prone areas ecclesiastic complexes, including churches, bell towers, monasteries, basilicas, synagogues, cathedrals and so on, have shown to be very susceptible at damage, even with partial or total collapses, when undergoing earthquakes. Indeed, these constructions, which are usually designed to withstand gravity loads only, are characterised by slender walls, lack of horizontal floors, bad quality of the masonry apparatus, ineffective connections among walls and between roof and walls and absence of tie-beams able to absorb the thrusts of arches and vaults. All these issues are responsible of the damages suffered by these structures, as detected after the last Italia earthquakes, such as those occurred in L’Aquila (2009), Emilia-Romagna (2012), Central Italy (2016) and Ischia (2017). In the current paper the seismic vulnerability assessment of the bell tower of the SS. Rosario ecclesiastic complex in Finale Emilia (district of Modena, Italy) is presented and discussed. After the geometrical and structural surveys of the whole masonry structure have been performed, the global seismic analysis of the bell tower by the 3Muri analysis software has been done. In particular, the behavioural differences between the isolated condition of the tower and the case within the ecclesiastic complex have been highlighted, showing the aggregate beneficial effect. Finally, proper retrofitting interventions have been designed and applied to the masonry bell tower, considered both as isolated construction and aggregate one, and the different benefits deriving from these interventions in the two inspected cases have been emphasised.

Evaluation of the temperature pattern of a complex body from thermal imaging and 3D information: A method and its MATLAB implementation

The standard setting of a camera used in Infrared thermography (IRT) is based on the choice of the same values of emissivity and distance for all pixels of a thermal image even if the emissivity depends on the relative position of camera and observed surface. Often this is not a problem. However, the resulting temperature pattern could be inadequate if a body having a complex shape is observed from strongly constrained positions. In order to face this issue, a procedure aimed at providing a correct temperature pattern by using 3D information related to a point cloud is proposed together with its MATLAB implementation (COMAP3 toolbox). For each pixel of a thermal image, the relative position of camera and observed surface is estimated, leading to pixel-specific values of emissivity and distance. The temperature obtained in this way is also mapped onto the point cloud. The effectiveness of the procedure in recognizing areas characterized by peculiar thermal behavior is shown in the case of a historic cylindrical masonry bell tower (Caorle’s bell tower, Venice, Italy).