Structural and seismic design
Structural design in a region where the earthquake sets the numbers.
Ivan Nozzi is an Ingegnere — an Italian-registered civil engineer — practising from Torrevecchia Teatina in the province of Chieti. He prepares structural calculations for new work, seismic assessments of existing buildings under NTC 2018, and lodges the seismic filing with the competent regional office.
The starting point
When Italian law requires a structural design
A structural design is required in Italy whenever the work changes the way a building carries load: a new build, an opening cut into a load-bearing wall, a floor replaced, a roof rebuilt, an internal staircase moved, an extension, an added storey. In Abruzzo a second thing is always true — the seismic action forms part of the calculation for every structure, and in most cases it is the load case that sizes the work rather than gravity.
The seismic design action is specific to the site, not to a regional label. NTC 2018 (Decreto Ministeriale of 17 January 2018, Italy's technical standard for construction) derives it from the coordinates of the plot, the design working life of the structure, its use class, and the subsoil and topographic categories. Two houses a few hundred metres apart, on different ground, receive different design actions. What the municipality's seismic zone governs is the procedure: which filings need prior authorisation and which are simply deposited.
My role covers the calculations, the verifications, the construction drawings, the seismic filing and, where agreed, supervision of the structural works. It deliberately does not cover everything a British or Irish reader might expect from a single consultant. The geological report is signed by a geologo, a separately registered geologist. Material testing is carried out by a laboratory authorised under article 59 of DPR 380/2001: I specify the tests, attend them and interpret the results, but I do not run them.
NTC 2018 · chapter 8
The three categories of work on an existing building
Chapter 8 of NTC 2018 sorts every intervention on an existing building into one of three categories. Which one applies is not a matter of preference: it follows from what the work does to the structure, and it decides how far the verification must go, what the job costs, and what may honestly be claimed once the builders have left.
| Category | What it is | When it applies | What it involves | What it does not deliver |
|---|---|---|---|---|
| Local repair or local intervention (§ 8.4.1) | Work on individual elements — a lintel, a section of wall, a beam, one floor — that does not substantially change how the building behaves as a whole. | Repairing damage, strengthening a single element, forming a modest opening, replacing a floor without a significant change in stiffness or mass. | Verification confined to the part affected: you demonstrate that local safety has not been reduced. A report and drawings are still required. | It produces no figure for the seismic safety of the building as a whole. After a local intervention the house is what it was before. |
| Seismic improvement — miglioramento (§ 8.4.2) | A set of works that raises the existing structural safety without having to reach the level required of a new building. | Chosen when the vulnerability of an existing building should be reduced but full upgrading is neither compulsory nor economically sensible. | A safety assessment before and after: the index ζE — the ratio between the seismic action the structure can withstand and the action a new building on the same site would be designed for — is calculated in both states and the gain is documented. | It does not bring the building to new-build level, and it does not permit an added storey or a structurally connected extension. Those fall under adeguamento. |
| Seismic upgrading — adeguamento (§ 8.4.3) | A set of works that brings the building up to the safety level NTC 2018 requires for that structure. | Compulsory in the cases the code lists: adding a storey, extending with structurally connected new parts, changing use class or use so that total foundation loads rise by more than 10 per cent, or a systematic set of works that turns the building into a different structural system. | Assessment extended to the whole structure, foundations included. For an added storey, for an extension structurally connected to the existing building, and for conversion to a different structural system, ζE must reach 1.00. Only for a change of use class raising vertical foundation loads by more than 10% does the code accept ζE of not less than 0.80. | It is not a guarantee against damage. NTC 2018 verifies limit states; it does not promise that an earthquake will leave the building untouched. |
Source: Decreto Ministeriale of 17 January 2018, chapter 8, § 8.4. For use class III school buildings and use class IV buildings, ζE after an improvement scheme may not fall below 0.60. When a listing describes a house as “seismically improved”, it names a category, not a level: ask which index was reached, before and after.
Method
What a structural assessment of an existing building involves
A structural assessment is built on knowledge of the actual building, not on design assumptions. NTC 2018 ties the confidence factor to the knowledge level reached: FC 1.35 at LC1, 1.20 at LC2, 1.00 at LC3. Investigating less does not make the project cheaper — it penalises the design strengths of the materials and makes the strengthening scheme heavier.
- Archive research: the original structural design, the works notification lodged with the seismic office, later building applications, and any period test certificates for the materials.
- A geometric survey of the structure rather than the architecture: wall thicknesses and bond, floor spans and joist direction, beam and column sections, foundation levels where visible, and the joints with the neighbouring buildings.
- Identification of the structural system and its history: masonry, reinforced concrete, steel or a mixture; added storeys, extensions, partial demolitions, past movement and past repairs.
- Material characterisation: inspection openings, non-destructive testing and, where they are needed, destructive tests run by a laboratory authorised under article 59 of DPR 380/2001. The number of tests sets the knowledge level and therefore the confidence factor.
- Ground and foundation information: a geological report signed by a geologist, geotechnical investigation, inspection pits at the foundations where they can be reached, and a crack survey read for signs of settlement.
- Modelling and verification: local collapse mechanisms — in masonry, out-of-plane overturning of a wall is usually the first to trigger — together with overall behaviour, with ζE computed at the relevant limit states.
- A written report: what was observed, under what limits, which knowledge level was reached, what safety index follows from it, and which strengthening options would change it, set out by category and by order of magnitude of cost.
Villages and masonry
Buying a stone house in an Abruzzo borgo
A stone house in an Abruzzo hill village can be a sound purchase or an expensive structural problem, and the listing photographs will not tell you which. Buyers from abroad usually decide under time pressure, in an unfamiliar legal system, on the word of the person selling the house. Looking at the building through a structural lens before the compromesso is signed, rather than after, changes the outcome more than anything else on the checklist.
A few concrete things carry most of the weight. The masonry itself: squared or roughly broken stone, whether through-stones tie the two leaves of the wall together, whether the mortar is still cohesive or comes away as powder. The corners, because a poor connection between two walls is where out-of-plane overturning starts. Whether tie rods or a ring beam were ever fitted. What was done to the floors and the roof: a concrete slab or a heavy concrete roof cast onto weak masonry — a common 1970s “improvement” — adds mass at the top without adding strength, and leaves the building worse than it was.
Then look past the boundary. In an Italian borgo almost nothing stands alone. The house is normally one cell of an aggregato: it shares walls with its neighbours, was raised at different dates, and is constrained by whatever stands against it. Two practical consequences follow. Seismic behaviour is assessed on the structural unit, not on the four walls being sold. And some strengthening work needs the neighbours' agreement — a matter that belongs in the price negotiation rather than in the months after it.
No responsible answer exists before someone has seen the building and the papers. What can be said before a site visit is which questions to put to the seller and which documents to request from the agent. Both cost nothing, and they narrow the field quickly.
Recurring questions
Structural and seismic work: the questions I am asked most
These answers concern structural design and seismic assessment in Abruzzo and hold in general terms. A specific building requires its documents and a site visit before anything can be said about it.
Is my house safe in an earthquake?
No engineer can answer that remotely, and anyone who does is guessing. The seismic safety of an existing building is expressed as a number, the index ζE, and it is reached only after surveying the structure, characterising the materials and running the calculation. An assessment establishes the present level of safety and how far a given scheme would move it. It does not establish that the building will be undamaged: NTC 2018 verifies limit states and does not exclude damage.
What is the difference between miglioramento and adeguamento?
Miglioramento raises the existing safety of a building without having to reach new-build level. Adeguamento brings it to that level. The practical difference is twofold. Adeguamento is compulsory in the cases NTC 2018 lists — an added storey, a structurally connected extension, foundation loads up by more than 10 per cent, a change to a different structural system — and it requires verification of the whole structure, foundations included. With miglioramento the target is yours to set, provided it is calculated and stated.
Does every renovation need a structural design?
No. Rewiring, replumbing, replastering, new floor finishes, bathrooms and lightweight partitions do not need one. Anything that changes how load reaches the ground does: forming or closing an opening in a load-bearing wall, replacing a floor, rebuilding a roof, moving a staircase, adding a mezzanine. The preliminary check is short, and it belongs before the materials are ordered rather than after a builder has started.
What is the pratica sismica, and when is it filed?
The pratica sismica is the seismic filing for structural work, lodged with the competent regional office — in Abruzzo, the Genio Civile — under articles 93 and 94 of DPR 380/2001. It goes in before structural work starts, together with the design, the calculation report and the materials report. Where prior authorisation is required, work cannot begin until it is issued; for works of lesser significance, article 94-bis refers to the regional rules.
I live abroad. Can this be handled while I am not in Italy?
Yes, with one condition: someone has to get into the building. Archive research, calculation, drawings and the filing are done here without you. The survey and any testing need physical access, arranged with the seller, the agent or a key holder. You are welcome to write in English or German: enquiries in those languages are read and answered. The calculations, drawings and filings are drawn up in Italian, the language that carries legal effect in Italy, and meetings and site visits are held in Italian, so bring someone to interpret or ask me to suggest someone locally.
First contact
Describe the building and the work you have in mind
Send the municipality, the type of structure, the year of construction if you know it, and what you want to do. You get back an indication of which category of intervention appears to apply, which documents are needed to be sure of it, and how the engagement would be structured. Write in English or German if that suits you better: enquiries in those languages are read and answered. The work itself is carried out in Italian.