If the issue of seismic performance is analysed on the basis of the three fundamental parameters: mass, own period and ductility, it is easy to observe the substantial absence of the former at least as far as the metallic structural elements are concerned.

The metal structures belong to construction systems that usually include vertical closures and roofs made of lightweight prefabricated sheet metal panels with internal insulation layers, so the consideration of lightness extends to the construction as a whole.

As far as design choices are concerned, it is easy to be faced with inverted priorities compared to multi-storey buildings.

The masses are so small that the seismic action becomes secondary to the horizontal action due to the wind, proportional to the width of the surfaces. The project is often developed without resorting to seismic action reduction factors, and the advantages of adopting a steel construction for these structural types are emphasized in seismic zones.

In the wake of the disastrous seismic events in Umbria/Marche (1997) and Molise (2002), institutions and public opinion have given particular attention to the problem of earthquake protection.

The Government Authorities responsible for this purpose have consequently encouraged the development and publication of new regulatory codes:

• Ordinance 3274/2003, First elements regarding general criteria for the seismic classification of the national territory and technical regulations for construction in seismic zones, and subsequent amendments by the Presidency of the Council of Ministers;
• Unified Text of Technical Standards for Construction of 23 September 2005 by the Ministry of Infrastructure;
• Guidelines for the application to cultural heritage of the technical regulations of the Order P.C.M. 3274/03 of the Department of Civil Protection;
• Ordinance of the P.C.M. 3519/2006, General criteria for the lindivision of the seismic zones and for the formation and updating of the lists of the same zones (currently adopted and issued only by the Region of Tuscany).
• Technical standards for construction NTC 2008 and its application guide
  Until the recent publication of the:
• Technical Standards for Construction 2018. The Instructions for the application of NTC 2018 will also be published later.
• At local level, national legislation is complemented by regional laws and regulations which may also vary substantially from Region to Region.

The new NTCs include important innovations in seismic design. In particular, the assessment of seismic impact is based on the most recent research of the National Institute of Geophysics and Volcanology, which has made possible the publication on the web of interactive seismic hazard maps of the Italian territory.

The Superior Council of Public Works has then made available on the web the experimental Response spectra program useful for the evaluation of the response spectra representative of the components (horizontal and vertical) of the project seismic actions for the generic site of the national territory. By entering the coordinates and design characteristics of the site, it is possible to view and print graphs and tables related to the project seismic computation according to the Ministerial Decree 14.01.08 and NTC 2018.

The general criteria for the design and verification of structures in seismic zones and the specific rules for each building material are fully explained in chapter 7 of the text of the NTC and the Instructions and are fully in agreement with the contents of the Eurocodes. Finally, important innovations have been introduced in the field of Geotechnics, including design for seismic structures.

Once again, the introduction of new design codes and standards, as a new moment of deepening and cultural growth, is an opportunity for the construction world to improve the quality and safety of construction itself, as well as a valid verification of the potential of the new standard.

In such a context of thought and investigation, sector operators, Public Administration technicians, Universities, Professional Associations, manufacturers and producers are involved. Steel, today little used in Italy for the construction of civil and industrial buildings, has a further opportunity for development, being able to provide the necessary guarantees of performance and safety that are now explicitly required by NTC 2018 and the Eurocodes.

The use of elements in metal carpentry is always successful thanks to the typical peculiarities of steel such as:

• Lightness and resistance of the structural elements, made possible by a high weight/resistance ratio, a feature that, when it comes to it, makes it possible to simplify the transport and installation of the structures and minimize the side effects due to the increase in load and mass on existing structures;
• small dimensions of the structural elements, as a natural consequence of the high structural efficiency of steel, a quality that makes it possible to simplify the replacement and/or integration of existing works with reinforcing elements
• rapidity of construction, which is always desirable, but especially when the intervention is urgent or when a prolonged interruption in the use of the construction is not possible;
• reversibility of interventions, typicality of steel structures based on removable dry connections.

By seismic retrofitting we mean all those interventions to modify existing buildings in order to make them more resistant to seismic activity.

With a better understanding of the effects of earthquakes on structures and recent events, the need for anti-seismic adaptation of many existing structures has been acknowledged.

For the seismic retrofitting of an existing building, reference should be made to the Ministerial Decree of 14 January 2008 (NTC08), which defines the principles for the design, execution and testing of buildings.

NTC08 defines the three different types of intervention that can be undertaken:

• Adaptation measures: to achieve the safety levels required by the NTC;
• Improvements to increase existing structural safety without reaching the levels required by NTC;
• Any repairs or local interventions which involve insulating elements and which in any case lead to an improvement in pre-existing safety conditions.

• Raise the building;
• Enlarge the construction through structurally constructed works;
• Make changes in class and/or intended use involving increases in global loads in the foundation of more than 10%. It is in any case mandatory to proceed with local verification of the individual parts and/or elements of the structure, even if they affect limited portions of the construction.
• Carry out structural interventions aimed at transforming the construction by means of a systematic set of works leading to a different building organism from the previous one.

The interventions to adapt (or as in some cases, improve) a building seismically, vary according to certain parameters such as:

• Type of construction (if single or multi-storey);
• Type of supporting structure;
• The foundations of the building, i.e. the seismic zone in which the building falls and more generally the context in which the building is inserted.

RIBERI P. COSTRUZIONI sas deals with seismic adaptation and structural improvement works on existing buildings with the use of steel elements, a material that is often more and more suitable for solving this class of problems.

With its experience in the field of metal structures and constructions, RIBERI P. COSTRUZIONI is the right choice for the seismic adaptation of your building, whether it is a house or an industrial building, in compliance with all safety regulations currently in force.