Seismic design requirements for buildings

Due to its position and geographical conformation, Italy is periodically affected by seismic phenomena of various magnitudes. The four seismic hazard zones into which the Italian territory is divided range from zone 1, where the probability of a strong earthquake occurring is high, to zone 4, where the probability is very low.

To prevent any damage caused by an earthquake, it is advisable to carry out anti-seismic interventions on existing buildings. In the case of buildings considered strategic or with a public utility function (for example hospitals, schools and government buildings) such interventions are mandatory.

To establish which are the most suitable anti-seismic interventions, various parameters must be taken into consideration: the type of construction (single-storey or multi-storey), the type of load-bearing structure (masonry, reinforced concrete, wood), the foundations on which the building rests, the seismic zone and the context in which the building is inserted. Equally fundamental for the choice of the intervention is the advice of a competent technician, who conducts the appropriate diagnostic investigations and laboratory tests.

It is also important to distinguish between seismic improvement, aimed at increasing the anti-seismic safety level, and seismic adaptation, which provides for the achievement of the safety threshold required by law, based on the seismic zone in which the building is located.

So let's see what are the main types of anti-seismic interventions:

Consolidation of masonry: structural deficiencies and atmospheric agents can lead to subsidence and therefore make it necessary to reinforce floors and walls (load-bearing and non-load-bearing) through the use of fiber-reinforced plasters with polymeric matrix (FRP), carbon or glass fibres, of mortars and thermosetting resins.

Reinforcement of reinforced concrete or wooden structures: calculation errors during the dimensioning phase, wear and stresses can weaken the wooden and reinforced concrete beams, pillars and columns. For interventions on these structures, carbon fibers prove to be the most used, because they are light and quick to apply.

Structural reinforcement works on the floors: the use of connectors allows a thin slab to be superimposed on the existing structure, often made of concrete with an electro-welded mesh, connected to the existing floor.

Use of anti-seismic devices: energy dissipators are devices that disperse a large part of the energy transmitted to the structure during an earthquake, thus reducing the stresses in the structural elements; the seismic isolators are positioned between the foundations and the elevated structures to decouple the earthquake frequencies from the frequencies of the elevated structure and avoid the occurrence of resonance phenomena; the structural joints, on the other hand, allow the interruption of the continuity of a work and therefore avoid seismic damage to two contiguous areas.

Geotechnical consolidation: the improvement of the foundation soils is just as necessary as the rehabilitation of the structure.

Why carry out anti-seismic interventions and what are the benefits?

Anti-seismic interventions improve the safety of buildings and reduce both the extent of possible damage to the building and the risks to the lives of those who live there or are there in the event of an earthquake. The decrease in the seismic risk class, following the anti-seismic interventions, also makes it possible to increase the value of the property on the market.

What incentives are there for anti-seismic interventions?

Individuals and companies that carry out interventions for the improvement or seismic adaptation of buildings in high danger zones (1 and 2) and in zone 3 can deduct part of the expenses incurred from income taxes.

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