Anti-Seismic Marble Basements for High Vulnerable Statues in Italy: Bronzes of Riace, Annunciazione by Francesco Mochi, San Michele Arcangelo by Matteo di Ugolino

Gerardo De Canio, Simonetta Bonomi, Alessandra Cannistrà

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Bronzes of Riace at the Archeological Museum of Reggio Calabria, the Annunciazione by Francesco Mochi and the St. Michele Arcangelo by Matteo di Ugolino at the Opera del Duomo Museum of Orvieto, Italy. These basements are also useful for the preventive conservation of other high vulnerable statues with analogous reduced support at the base, such as the David by Micheangelo in Florence

 

Introduction

This paper describes the new anti-seismic basements made of marble for earthquake protection of high vulnerable statues of primary importance in Italy:

  • two Bronzes of Riace at the Archeological Museum of Reggio Calabria,
  • three statues at the Opera del Duomo Museum (MODO) of Orvieto, namely: the two marble statues of the Annunciazione made by Francesco Mochi, and the bronze statue of S. Michele Arcangelo made by Matteo di Ugolino da Bologna.

 

The new basements are also useful for other high vulnerable statues standing on their legs, e.g., the David by Michelangelo in Florence. The design approach of the basements was to confer the seismic isolation property to the geometry of the surfaces, according to the following design targets: maximum seismic isolation, low stiffness and low dissipation; reversibility; full compatibility of the materials; easy maintenance.

 

Anti-Seismic Basements for the Bronzes of Riace

The two statues, “Bronze A the young” and “Bronze B the old”, were previously located at the ground level of the museum and provided with laminated rubber anti seismic devices. Moving the statues from the ground level to the new exposition room on the first floor of the museum required the upgrading of the basements according to the new seismic classification of the site and the change in the maximum hazard spectra. The previous devices inserted in the old basement provided a seismic isolation coefficient value of 2.5-3 and, to avoid overturning, the statues where anchored with strengthening forces of 1800N applied to each shoulder by means of steel cables inserted in the cave legs (ref. [1]). The need to reduce the strengthening anchoring forces, together with the new expected seismic demand due to the new seismic classification, induced to re-design the anti-seismic basements to increase the isolation coefficient, reducing the risk of exceeding the seismic capacity of the two statues.

The design results are, for each statue, a basement made of two blocks of marble type Carrara, showed in Fig. 1, and the surfaces of the blocks modelled as an ellipsoid of revolution, where 4 spheres made of the same material of the blocks are located. In short, the basement is made of the following elements: BI= marble lower block, S= marble spheres, DO= Horizontal displacement limitation and re-centering device, BS= marble upper block, DV=vertical isolation device inserted in the BS upper block.

 

DeCanioBonomi fig1

Fig. 1. Marble anti-seismic basement for the Bronzes of Riace
Source: ENEA

 

However, stiffness and principal frequency of the basement are not constant, due to the elliptical geometry of the rolling surfaces, the principal frequencies are ranging from 0.015Hz to 0.025 Hz depending on the position along the surface, with zero value at the centre, where the re-centering function is demanded to the element DO. The vertical isolation is provided by two stainless steel plates connected by four shock absorbers made of dissipative cables plus four springs inserted in piston guides confining and de-coupling the vertical and the horizontal motions, therefore the horizontal isolation is demanded to the basement geometry and the vertical isolation is demanded to the shock absorbers inserted in the upper basement.

 

DeCanioBonomi fig2

Fig. 2. Marble basement for the Bronzes of Riace: a) Details of the vertical isolation device inserted into the upper block, b) Basement ready for the shaking table tests
Source: ENEA

 

Shaking Table Tests

The shaking table tests on the basements have been performed at the Qualification of Materials and Components Laboratory of the ENEA Casaccia Research Centre, Rome (Italy); test set-up and details of the basements are showed in Fig.3:

 

DeCanioBonomi fig3

Fig. 3. Shaking table tests of the marble anti-seismic basements for the Bronzes of Riace (ref. [2]): a) test set-up, b) test acceleration spectra at the base table
Source: ENEA

 

The input time histories were natural accelerograms rescaled to the max hazard of Reggio Calabria, return period of 2475 years, amplified on the first floor of the museum. Also three artificial accelerograms were applied, compatible to the Ultimate Limit State of the museum amplified on the first floor at different damage conditions of the building. At the end of the test campaign were three X,Y,Z accelerograms also applied, compatible with the RRS (Required Response Spectrum) for NPP (Nuclear Power Plant) class 1-E equipment (essential for safety) in compliance with the IEEE-344 specifications. All tests reached the reduction coefficients of 15-20 for the horizontal accelerations and 2.5-3 for the vertical accelerations; the overall maximum acceleration measured on the basement in all the tests was 0.08g.

During the tests with natural earthquake, the max acceleration peak on the basement was 0.062g. In the vertical direction, with Peak Floor Acceleration PFA=2g, with isolation coefficient 2.4 and max basement vertical acceleration 0.86g.

 

DeCanioBonomi fig4

Fig. 4. a) Floor-Nat1, F1_Tx,y= base table, F1_Bx,y= basement. Isolation Coeff.= 22; b) shaking table test Floor-Nat2, isolation Coeff.= 20
Source: ENEA

 

The two forces of 1800N at each leg to prevent overturning are not yet necessary and have been reduced to 600N and 300N in the new basement, just to replace the weights of the shield on the left arm and the lance on the right arm.

DeCanioBonomi fig5a

Fig. 5. Bronze A: comparison of the stress fields by the old and new strengthening forces
Source: ENEA

 

Anti-Seismic Basements at the Opera del Duomo Museum, Orvieto, Italy

In this chapter the anti seismic basements for the two marble statues of the Annunciazione by Francesco Mochi, and the bronze statue of S. Michele Arcangelo at the Opera del Duomo Museum of Orvieto in Italy are described, as well as the design of the basements for the 12 statues of the St. Apostles, either if the 12 statues will be repositioned in the Cathedral or in the annexed Museum.

 

green arrowAnnunciazione by Francesco Mochi

Devices of the same family as those for the Bronzes of Riace have been developed for the Annunciazione by Francesco Mochi at the Cathedral of Orvieto (Fig. 5)

 

DeCanioBonomi fig6

Fig. 6. The Cathedral of Orvieto (Italy) and the two statues of “The Annunciazione” by Francesco Mochi
Source: [3]

 

The devices, made of black granite, will be positioned on the original basement  and covered with the same stone.

DeCanioBonomi fig7

Fig. 7. Original basement composed of several blocks
Source: ENEA

 

DeCanioBonomi fig8

Fig. 8. The anti-seismic basement for The Annunciazione by Francesco Mochi
Source: ENEA

 

The two statues representing The Annunciazione, together with other 12 statues representing the St. Apostles were removed from the Cathedral of Orvieto in the XIX century. The rendering in Fig. 9 show the statues of the 12 Apostles as they will look if repositioned in the Cathedral. In the figure the design of the anti-seismic device for the 12 statues is also represented, either if they will be repositioned in the nave of the cathedral or in the Museum.

DeCanioBonomi fig9a

Fig. 9. Image rendering of the repositioned statues of the 12 Apostles in the Orvieto Cathedral (ref. [3]) and the Black Granite anti-seismic device (Source ENEA)

 

green arrow S. Michele Arcangelo by Matteo di Ugolino

Figure 10 represents the bronze statue of S. Michele Arcangelo on the façade of the Cathedral and the design of the new basement with the granite anti-seismic device. This statue was heavily deteriorated by severe weather conditions and large oscillations due to inadequate strengthening forces, therefore the statue was removed from the façade and then moved into the museum, at the end of its restoration.

 

DeCanioBonomi fig10

Fig. 10. S. Michele Arcangelo on the façade of the Cathedral and design of the basement for the museum exposition (Source: ENEA)

Marble Basement for High Vulnerable Statues: Proposal for the David by Michelangelo

The David by Michelangelo in Florence, Italy, one of the statues of the absolute importance ever acknowledged by humankind, is highly vulnerable to earthquakes because it is standing directly on its feet and because the legs are seriously cracked. Therefore, the same type of basement can be useful to protect this statue from earthquake-induced overturning and shear stress. In this case, due to the mass of the actual basement and statue, a marble basement of 2m x 2m with 25 spheres as shown in Fig. 2, are needed.

 

DeCanioBonomi fig11

Fig. 11. Proposal for the base isolation for the David by Michelangelo
Source: ENEA

 

Conclusions

New anti-seismic basements made of marble have been developed for high vulnerable statues in Italy. For the Bronzes of Riace, the very low acceleration at the base of the statues allows to reduce the strengthening forces to the values equivalent to the shield on the left arm and the lance on the right hand. Basements of the same family have been used for the two statues of the Annunciazione by Francesco Mochi, and the St. Michele Arcangelo by Matteo di Ugolino at the Opera del Duomo Museum of Orvieto, Italy. Analogous basements have been designed for the statues of the 12 Apostles to be positioned either in the Orvieto Cathedral or in the annexed museum.

The results allow to propose the same type of basement for David by Michelangelo in Florence, Italy.

 

Acknowledgements

The authors wish to thank Roberto Ciabattoni and Paola Donati of ISCR, restorators of the Bronzes of Riace and the S. Michele Arcangelo; the ISCR Director, Dr. Gisella Capponi, for the supports to better configure the basements of the Bronzes of Riace; Elisabetta Andreani of OPSM for the studies of the Orvieto Cathedral; the ENEA researchers Alessandro Colucci and Francesco Di Biagio for shaking table tests and data acquisition, Ivan Roselli for 3DVision data acquisition, Marialuisa Mongelli for Numerical Analysis and Model validation, Angelo Tatì for the NDT investigations, Massimiliano Baldini, Stefano Bonifazi and Alessandro Picca for test set-up and laboratory experiments.

 

References
  1. A.M. Vaccaro, G. De Palma, 2003: I bronzi di Riace, Restauro come Conoscenza. Artemide Edizioni, ISBN 88-86291-73-6.
  2. De Canio, G. (2012). Marble devices for the Base isolation of the two Bronzes of Riace a proposal for the anti seismic basement for the David of Michelangelo. The 15th World Conference on Earthquake Engineering, September 22-29, 2012, Lisbona, Portugal.
  3. Alessandra Cannistrà (2006): Da Simone Martini a Francesco Mochi - Verso il nuovo museo dell’Opera del Duomo di Orvieto.  Silvana Editoriale S.p.A. ISBN 88-366-0704-7.

 

Per informazioni e contatti: infoEAI@enea.it


Gerardo De Canio - ENEA, Unità Tecnica Tecnologie dei Materiali

Simonetta Bonomi - Soprintendente per i Beni Archeologici della Calabria

Alessandra Cannistrà - Curatore Museo OPSM - Opera del Duomo di Orvieto