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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., This work was performed in the University of Minho with the funding from the ELARCH Program (Euro-Latin America partnership in natural Risk mitigation and protection of the Cultural Heritage), an Erasmus Mundus Action 2 Partnership (552129-EM-1-2014-1-IT-ERA MUNDUS-EMA21) by the European Commission and coordinated by the University of Basilicata, Italy.

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.

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.

The historical and architectural heritage preservation is a very important task for seismically vulnerable European countries. Medieval masonry towers and bell towers in churches are quite diffused all over Europe as an essential part of the cultural heritage to be preserved. In fact, recent earthquakes highlighted that ancient masonry towers are particularly susceptible to either partial or total collapse under seismic excitations but modelling their behaviour at various levels of accuracy is still an open field of research. In order to shed some light on the role played by aggregate buildings on the seismic response of historic towers, their safety assessment is investigated in the current paper starting from the case study of the Sciri tower in Perugia. Firstly, linear dynamic analysis by means of the SMuri software is conducted with the aim to identify the main vibration modes of the tower. To this purpose, the tower is modelled both as an isolate structure and in aggregate condition within the urban built-up. Subsequently, the numerical fundamental period of the tower is compared with results deriving from different literature empirical methods in order to find the most effective predictive relationship. Finally, the seismic behaviour difference between the isolate tower and the aggregate one is assessed in terms of vibration periods, focusing, in particular, on the variation of vibration frequencies associated to the variation of the tower free height from the ground.

We present an innovative application of a non-destructive approach for the mechanical characterization of historical masonry structures, based on the analysis of their dynamic response. The proposed approach exploits the extraction of modal parameters to define mechanical features of the structure such as mass, damping and stiffness matrices by means of Operational Modal Analysis, starting from measurements performed by a very promising, expeditious and contactless experimental technique based on radar interferometry. This approach may be very effective for structural health monitoring purposes. In particular, we apply this technique to a historical masonry bell tower with the aim of detecting and consequently solving some of the experimental challenges arisen in some previous experimental campaigns.

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.

The seismic safety of two medieval masonry bell towers in Italy is investigated. At first, compressive tests, flat jacket tests and environmental vibration measurement are used for structural identification. In particular, a vibration-based procedure is used to investigate the dynamic features of monuments dealing with the uncertainties due to the mechanical characteristic of the material. The procedure is based on a typical finite element (FE) model updating technique using environmental vibration test results. The updated FE model of the towers is defined from a set of parameters minimizing an error criterion relative to modal properties. A satisfactory improvement on modal parameters which is in close agreement with the experimental results is found. The seismic assessment is carried out with nonlinear static analysis of the tower under multimodal distributions of lateral loads. Nonlinear analysis shows the potential collapse mechanisms and evidences the dangerous characteristics which may play a role in seismic vulnerability of the towers. A displacement-based version of the capacity spectrum method based on the inelastic demand spectra is finally used to evaluate the seismic performance of the towers at the different limit states.