Dora Foti. The aim of the paper is to assess the dynamic behavior of the bell tower of the 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. The tower is totally disconnected from the structure of the Church. It was considered the effect of ambient vibration force and, for the forced tests, the excitation produced by different bells. Four bells are housed in the bell chamber, while four more bells are housed at a higher level. All the bells are directly connected to the tower so that their movement introduce an excitation swinging force to the tower. The accelerations at different points have been recorded by 11 piezoelectric accelerometers positioned at four levels of the bell tower. The results of the experimental tests have been analyzed in order to estimate the modal parameters of the tower and to calibrate a 3D finite element model of the tower useful to check the vulnerability of the tower.

1. Dynamic Behavior of a Historical Tower Subjected to Bells’
Forced Vibrations
Dora Foti– Polytechnic University of Bari

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The bell tower in Bitonto (Bari), Italy, is an important symbol of
the town. It dates back to 1974 and is situated near the older
“Basilica dei Medici”.
The tower is about 54m tall and has 7 floors characterized by
different interstory heights; the plan is square and measures
11.87 m².
The seven levels of the tower consist of a basement 3.35 m
tall, the first floor 5.44 m tall and other six floors 4.42 m tall
each. At the 7th floor there is the “Belvedere” terrace and then
two bell chambers with 8 bells.
The bell tower is made of reinforced concrete frames and
columns with variable sections.

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Foti – Dynamic behavior ofa historical tower subjected to bells’ forced vibrations

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Foti – Dynamic behavior ofa historical tower subjected to bells’ forced vibrations

7. Number of bell Name of bell Diameter (Φ) Weight
1 Santi Medici 105 cm 750 kg
2 Aurelio Marena 93 cm 550 kg
3 Il signore è presente
e ti chiama
83.5 cm 400 kg
4 Isabella Ciccolella 78 cm 350 kg
Disposition of main bells
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Lower bell chamber

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The bell tower has been modelled with SAP2000 software.
The columns are modelled with a section linearly variable.
The external masonry wall is modelled as a distributed load on the frames.
The material used is concrete C16/20.
The natural frequenciesof this preliminarymodel for the structure are:
- Mode 1: f=0.92 Hz - bending mode X-axis
- Mode 2: f=0.95 Hz – bending mode Y-axis
- Mode 3: f=1.35 Hz – torsional mode
Preliminary model-Modal Analysis

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Equipment used for the tests
The tower was instrumented with twelve uniaxial piezoelectric accelerometers (PCB Model: 393B31) placed in
N-S and E-W directions.
They were connected to an acquisition system (NI-9234) through coaxial cables.
The control unit was located at the 5th floor where positioned the NI system, a controller Compact DAQ and a
laptop.

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Position of the accelerometers
The acquisition data in obtained
using different sources:
- Ambiental Noise;
- Swinging of the bigger bell (SS
Medici) alone;
- Swinging of the second bigger
bell (Aurelio Marena) alone;
- Swinging of the bell Isabella
Ciccolella alone;
- Swinging of all bells together.

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Foti – Dynamic behavior ofa historical tower subjected to bells’ forced vibrations

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node(1,1)=node(2,1)
node(1,2)=node(4,2)
node(3,1)=node(2,1)
node(3,2)=node(4,2)
node(1,3)=node(2,3)=node(3,3)=node(4,3)=0
node(7,1)=node(8,1)
node(5,2)=node(8,2)
node(7,2)=node(6,2)
node(5,1)=node(6,1)
node(11,1)=node(12,1)
node(9,2)=node(12,2)
node(9,1)=node(10,1)
node(11,2)=node(10,2)
An easier model of the bell tower is done in Artemis.
Have been inserted the channels in their real position and have been imposed
the nodes’ equations.
Artemis model - Operational Modal Analysis

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Acquisition data forAmbiental noise

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The resulstof analysis
(Method OMA-SSI-UPC) ofArtemis
for Ambiental noise are:
- f1=1.30 Hz
- f2=1.35 Hz
- f3=2.69 Hz
The SAP model is modified to obtain the same natural frequences of
Artemis indroducing:
- Elastic Modulus E= 65000N/mm²; this value is necessary to considerate
the stiffness of external masonry;
- Density γ= 20 kN/m³
Preliminary ModelPreliminary Model Calibrated ModelCalibrated Model
f1= 0.92 Hz f1=1.29 Hz
f2= 0.95 Hz f2= 1.33 Hz

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Name File Channel 1 (acceleration) Channel 2 (acceleration) Description
Bitonto-Campane 1 0.056 g 0.057 g The bigger bell
SS Medici alone
Bitonto-Campane 2 0.062 g 0.085 g The second bigger bell
Aurelio Marena alone
Bitonto-Campane 3 0.098 g 0.125 g Bells all together
Bitonto-Campane 4 0.035 g 0.043 g The bell
Isabella Ciccolella alone
Bitonto-Campane 5 0.045 g 0.052 g The bell
Isabella Ciccolella alone
This acceleration results are obtain only with channels1 and 2 (those placed above) because the effects of the bells’
swinging is higher.
From the recorded data it is noticed that the maximum acceleration is when the bells swing all together.
Max accelerations of the bells

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A visual analysis of the structure
shows that the introduction of vibration
associated with the swinging of the
bells have provoked the expulsion of
the cover.
Then the reinforcement, interacting
with the air, is corroded. This effect
over the time can also be very
dangerous for the structure even for
vertical loads.
Future developments of the following
study include:
- Comparison with STRAUS7 Model
- To analyze the dynamic behavior of
the structure when the bells swing

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Thank you !!