PSI - Issue 29

Leonardo Zaffi et al. / Procedia Structural Integrity 29 (2020) 157–164 Zaffi, Capestro and Viti / Structural Integrity Procedia 00 (2019) 000 – 000

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chords, would have the advantage not to overload the system; in this case, however, it would be difficult to assure to the sculpture the due stability in case of strong wind. At the opposite, a strong fixing disposa l should give a higher stability to the system, but it would substantia lly change its globa l mass, requiring much more attention to the connection with the building. Moreover, it would be very different in stiffness and mass by the wood truss “nose”, presentingpossible interaction problem. Another substantia l issue was about who had to be in charge of the lega l responsibility of the system safety. Indeed, even if the entire process was developed within the University, the Rea l Esta te Company was responsible for its management. The power station, in fact, was owned by the Rea l Estate Company until it is fina lly refurbished and transferred to the Municipalityas a part for theurbanization fees of the area. Despite the hazard rela ted to the suspended sculpture was negligible, the Rea l Estate Company could not avoid to face the technica l legislation. The proper procedure to represent the structura l behavior of the sculpture was not easy to understand. Florence, like a lmost any other town in Ita ly, is subjected to a moderate seismic hazard, and a ll the architectura l interventions must be checked in order to assess their structura l and seismic safety. In this case, however, there was not a structura l project, and even the geometry of the truss system was created time-by-time, without a precise scheme. Moreover, the acceptance criteria provided by the Technica l Code refer to more conventiona l structures, and they cannot by simply extended for systems so much different to them. Therefore, the structura l problems to face would be: i) gettinga structura l scheme of the system, ii) representing the strength of the connections, iii) finding referenceresponsequantities to compare to thestructural behavior of thesystem. The representation of the structura l scheme requires a laser-scanner survey, to be done getting into the sculpture. The process followed for the construction, in fact, was only partia lly planned, and severa l changes have been made on the basis of observations rela ted to thequality of the obtained results. The modeling of the joints (see Figure 7) was a problem not easy to overcome. They have been done by not qua lified operators, without a standard qua lity-controlled process. Moreover, each connection has been de-assembly and re-assembly, as a consequence of the transportation need. The qua lity of each connection, therefore, could be different from the others, for the occurring of imperfections or the degrade of the wood subjected to the repeated works.

a

b

c

Fig. 7. Connections of the wood-truss system and the steel plates for the connection to the building.

Fina lly, the verification of the safety of the structure would be easy to pursue only in terms of elastic stress; the amount of latera l displacement, indeed, would need of reference parameters which a re provided by the current Code

only for very different structures. 4.2 (Lack of) technical provisions

The need to face the Technica l Codes prevented the respect of the initia l schedules. The Company had to take some time to face these problems, and it decided to ca ll an engineer with a specific experience in checking the structura l behavior of temporary and unconventiona l structures. The procedures and the assumptions to adopt in case of new buildings and structures (NTC 2018, Circolare Ministeriale 2019) are very efficient and easy to understand.