Resonances detected on a historical tower under bells’ forced vibrations

Dora Foti,Vitantonio Vacca,David Bru,Mariella Diaferio,Salvador Ivorra

doi:10.3221/igf-esis.46.19

Dora Foti, Vitantonio Vacca + Show 3 more

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https://doi.org/10.3221/igf-esis.46.19

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Abstract

The aim of the paper is to perform a preliminary assessment of the dynamic behavior of the bell tower of Basilica Church “S.S. Medici”, one of the most important church in the town of Bitonto, Bari, Italy. The tower is 55 m tall and it is made in reinforced concrete. It is totally disconnected from the main structure of the Church. The structural behavior of the tower has been investigated by performing dynamic experimental tests, which have been executed in two different forcing conditions: recording the vibrations induced only by ambient loads, and, then the ones due to ambient loads and to the excitation produced by the bells. Four bells are housed in the lower bell chamber on a concrete bell frame, four more bells are housed at a higher level bell frame. All the bells are directly connected to the tower and swing in the same direction, so that their movement introduces a dynamic excitation on the tower. The experimental records have detected excessive movements on the tower when bells swing.

Highlights

The preservation of the cultural heritage is a topic of great importance for our societies
After the Finite Element Analysis and the Operational Modal Analysis, it is possible to conclude that the mode shapes associated to the main frequencies are no pure bending modes in the N-S or E-W directions, the two main modes having a diagonal component associated to a deviated bending due to the internal stiffness of the tower
The main frequencies and mode shapes have been investigated by numerical models and by an experimental campaign applying Operational Modal Analysis

Summary

Introduction

The preservation of the cultural heritage is a topic of great importance for our societies. Among the typologies which are wide spread in the Italian building patrimony, the towers are the ones characterized by a high slenderness and, may be more vulnerable to horizontal forces like the ones induced by wind, earthquake or bells’ swinging Due to this characteristic, these structures may be investigated by means of in-situ dynamic tests, which have the advantage of allowing a description of the global behavior. Many studies have been carried out adopting the aforementioned dynamic experimental techniques but almost all the examined cases deal with the evaluation of the modal parameters of masonry towers [9,10,11] Many of these researches use the results of the modal parameters’ identification to evaluate the unknown mechanical characteristics. Some authors studied the effect of these vibrations on the interaction with the bell tower such as in [12,13,14]

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