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Seismic risk classes, deductions, interventions and technical solutions for masonry and reinforced concrete buildings: the framework on the 2017 Sisma Bonus and a handbook to download
With the Sisma Bonus made official with the Ministerial Decree of 28 February 2017, the Ministry of Infrastructure and Transport has implemented the indications introduced with the 2017 Stability Law (Law no. 232 of 11 December 2016) through which the Government has provided for the introduction of a series of financial measures to promote the mitigation of the seismic risk of the Italian building heritage through the citizens’ initiative.
These measures, in the form of increasing tax deductions, are aimed at rewarding all those interventions carried out on homes, buildings used for productive use and common parts of condominiums that will allow the transition to lower seismic risk classes than the initial state.
But what are the types of intervention capable of allowing this passage? To explain it to you, we have produced the document: “Sisma Bonus 2017 – Practical Guide and Handbook of Interventions”. Let’s see what it is.
What is the Handbook of Interventions
The handbook is a special one created by the Kimia Technical Office and is structured in such a way as to present some typical problems found in masonry and reinforced concrete buildings (e.g.: lack of connection of the horizon with the wall panels, deficiencies in the joints between structural elements, etc.) and then propose a series of intervention solutions consistent with the categories provided for in the Guidelines for the classification of seismic risk of buildings.
The document is available for download at the bottom of the article but first we advise you to read the essential points of the 2017 Sisma Bonus.
Seismic risk classes
The “Guidelines” with Annex A of Ministerial Decree 65 of 7 March 2017 define eight risk classes for buildings, from the letter A+ (less risk) to G (more risk), identified on the basis of two parameters:
- “Expected Average Annual Loss” (PAM), understood as the cost of repairing the damage produced by seismic events that will occur during the useful life of the building, broken down annually and expressed as a percentage of the reconstruction cost.
- “Safety Index” (IS-V) or “Risk Index”, defined as the ratio between the peak acceleration on the ground that determines the achievement of the “Life Saving Limit State” and that expected, on site, for a new building.
The designer in charge must determine the risk class to which the building belongs and the related interventions to be carried out in order to obtain a reduction in the risk itself and access the benefits provided for by the 2017 Stability Law.
Deductions
The building support actions provided for in the 2017 Stability Law for all buildings falling within seismic zones 1, 2 and 3, as defined by Ordinance PCM 3274/2003, guarantee variable deductions ranging from a minimum of 50% up to a maximum of 85%. Let’s see in detail the deductions provided for depending on the case.
For all buildings, both residential and productive, the minimum deduction is set at 50% (without change in class). For individual real estate units, both for residential and productive use, the deductions are instead high at:
- 70% if the intervention involves the passage of a risk class;
- 80% if the intervention involves the passage of two risk classes.
For condominium buildings (even below 8 real estate units, only for interventions relating to the common parts), the deductions are raised to:
- 75% if the intervention involves the passage of a risk class;
- 85% if the intervention involves the passage of two risk classes.
The deductions are applicable up to a maximum expenditure ceiling of 96 thousand euros per year for each real estate unit and are deductible in the following five years.
Risk class assessment
The designer can use two different methods to carry out the assessment of the seismic risk class:
- conventional: applicable to any type of building, it is based on the application of the structural analysis methods provided for by the current Technical Standards in force. From their application, the accelerations associated with the different limit states for the building under consideration are extracted, from which it is possible to determine the PAM and IS-V parameters of the structure and consequently the risk class to which it belongs, understood as the worst identified by the aforementioned parameters.
- Simplified: applicable in the case of masonry buildings, it provides for the determination of the vulnerability class through the “European Macroseismic Scale” (EMS). The vulnerability class, together with the seismic zone to which the building belongs (see Ordinance PCM 3274/2003), makes it possible to identify the risk class of the building.
As far as the application of the conventional method is concerned, it is not possible to propose a priori a series of interventions that allow the start of one or two classes, but everything is left to the preliminary analyses conducted by the designer on the building and to the design choices.
For the application of the simplified method , on the other hand, it is the “Guidelines” themselves that establish categories of intervention that allow the reduction of vulnerability even if only by one class. These interventions, valid for masonry buildings, although with limitations, are extended to reinforced concrete buildings and buildings for production purposes, similar to industrial warehouses.
Masonry buildings: categories of intervention
For masonry buildings, the increase of a risk class can be considered and access to the 70% contribution in the event that all the interventions belonging to the categories indicated by the Guidelines for each type of masonry texture are carried out. In this regard, see table 6 of Annex A of Ministerial Decree 65 of 7 March 2017 (“Simplified approach for interventions on masonry constructions – Local interventions necessary to reduce the vulnerability of a single class”).
These are the seven categories provided:
- Restoration of damaged and/or degraded areas;
- Elimination of unopposed horizontal thrusts;
- Out-of-plane stabilization of large walls;
- Connection of the wall panels to the horizontals;
- Safety of non-structural elements;
- Elimination of empty thrusts;
- Stabilization of the internal face of wall panels with air chamber.
In the document “Sisma Bonus 2017 – Practical guide and handbook of interventions” a series of interventions for each of these seven categories are reported. Below we will see an excerpt of what you will find in the Handbook, i.e. two cases of restoration of damaged and/or degraded areas.
For all other interventions, including those on reinforced concrete buildings and for industrial use, we invite you to download the document at the bottom of the article.
Masonry buildings: the restoration of damaged or degraded areas
Problem: presence in the wall panels of deep cracks and/or heavily damaged material.
Solution: Stitch and sew.
Intervention: local replacement of the cracked walls by reconstructing the wall face with new material, inserted in such a way as to restore the structural continuity of the element. The phases envisaged are:
- removal of damaged parts around the lesion: stone material, bedding mortar and all inconsistent parts;
- washing of the masonry;
- recomposition of the masonry with stones or solid bricks laid with Tectoria M15 lime-based mortar.
Variants: alternatively, it is possible to use Tectoria M10, Tectoria PMP or Limepor LGS products mixed with sands of suitable grain size as bedding mortars. In order to improve the adhesion with the existing masonry, the insertion of Kimisteel INOX X-BAR helical bars can be envisaged.
Problem: wall panel with well-preserved stone material but absence or erosion of the mortar joint with loss of surface binder function
Solution: Restyling the joints
Intervention:
- deep skiving of degraded joints until a compact support is obtained;
- cleaning by brushing and hydro-washing of all dust and detached materials produced by the previous operation;
- saturation of the substrate with water (saturated condition with a dry surface);
- repair of the joints with Limepor MT ready mortar after reweaving where necessary.
Variants: alternatively, Tectoria PMP or Limepor MT/F products can be used as mortars for styling in the case of restyling smaller than one centimetre. An improvement of the intervention can be achieved through the insertion of Kimisteel INOX X-BAR helical bars in mortar appeals.
Download “Sisma Bonus 2017. Guide and handbook of interventions”
To find out about the other types of intervention for masonry and reinforced concrete buildings, we invite you to download for free below: “Sisma Bonus 2017. Practical guide and handbook of interventions“.
Finally, if you are working on a project and need technical advice, we recommend that you visit the Design Support section and rely on our team of structural engineers.
