Improve the safety conditions of buildings
The safety of constructions has always engaged technicians, companies and government apparatuses, in seeking the most appropriate solutions, to guarantee ever greater safety in the various conditions in which a building may find itself.
The main scenario in which these studies have placed the most attention concerns the safety of existing buildings, especially in coincidence with natural events such as earthquakes.
The normative in force, fundamentally envisage three different types of interventions to safeguard the static safety of buildings, namely:
- seismic adaptation;
- seismic improvement;
- localized repairs.
The interventions of adjustment seismic, have the purpose to achieve the safety levels required by the regulations in force on the subject of earthquake-proof constructions, generally they are characterized by procedures very invasive and costly from an economic point of view.
Seismic improvement what the current regulations say
The improvement interventions seismic have as their objective, the increase of the safety level of the existing structure, without necessarily reaching the levels required by the specific standard on anti-seismic buildings.
For this reason, they result less invasive of anti-seismic adaptation interventions, as well as being less costly.
Finally, the interventions of repair or localized, are those that affect structural elements isolated, whose repair and consequent strengthening contributes to the improvement of the pre-existing safety conditions.
The current ones standards on the matter, contained in the DM 17/01/2018 and Circular 7/2019 provide for the first two interventions described above testing static, while for localized interventions the declaration of regular execution made by the construction manager.
What to check before implementing a seismic improvement project
Compared to previous regulations, the current technical standards have introduced a new concept, at the basis of the calculation relating to the static safety of a building, namely the relationship between the seismic action that the structure can bear and that which would be used in having to design a building from scratch.
Tale innovation legislation, requires a study more accurate about the intervention to be implemented in order to improve the static safety conditions of an existing building.
Therefore, in order to carry out an improvement project, it is necessary to evaluate that kind of seismic action is capable of to bear the construction in the state of fact in which it is found, in order to then be able to do so comparison to what he would be able to endure after the improvement intervention carried out.
What interventions to improve the structure
After exposing in a manner simplified even for those who are not insiders, the concept of seismic improvement , list below what are the interventions more frequent with which it is possible to improve the static safety conditions of a building, doing the necessary distinctions in relation to the different construction types.
It is in fact necessary to specify how these interventions are different, in relation to the structural typologies to which they are addressed, especially for the different type of behavior that these structural types denote, in the presence of a seismic action.
For buildings in masonry, the most commonly used interventions consist of injections of binder mixtures, together with reinforced restyling of the joints and applications of reinforced plasters.
In order to avoid out-of-plane expulsion of the wall faces, the tie rods performed with steel chains, performed horizontally and vertically.
Safe and minimally invasive interventions
With the use of carbon fibers, real ones are realized bandages containment of the entire wall box, thus avoiding its dismemberment in case of seismic stress.
This last intervention, although more expensive of the usual strengthening interventions, it has the advantage of being minimally invasive, thus allowing the inhabitants to stay in situ during the execution of the works.
For the most modern buildings, made with framed structures in reinforced concrete, it is possible to intervene both by reinforcing parts of the vertical structure such as pillars, walls, etc., and horizontal parts such as beams, floors, cantilevered slabs, etc.
Also in these cases the bandage of the nodal elements, beam-pillar, together with the Consolidation of horizontal structures, allows to obtain significant improvements of the structural response in the presence of a seismic action.
When structural deficits in part of the structure, such as, for example, a group of pillars arranged in different points, it is possible to proceed with real ones jacketing of these structures, through the use of angles and calastrelli, as well as using plating of the structural parts.
Safety a concept to be interpreted
The described interventions can be used separately or together, in order to reach the desired safety level, in relation to the class risk to which the building on which the intervention is carried out belongs.
The regulations in force, contained in the DM 17/01/2018 and Circular 7/2019, specify that:
For the seismic combination of actions, the value of ζE can be less than unity. Unless specific situations relating to cultural heritage, for class III buildings for school use and class IV, the value of ζE, following the improvement interventions, must in any case be no less than 0.6
From the provisions of the regulations, it appears for example how a school can be considered safety if its safety index is 60% of that of a modern school built with anti-seismic criteria.
This value, however, non represents a certainty in terms of the overall safety of the work, but indicates the value minimum to which reference should be made.
In fact, the same standards lay at the basis of a good seismic improvement intervention, l‘acquisition one level of knowledge of the building on which you intend to intervene.
level of knowledge of the structure the basis of the intervention
This knowledge must concern the construction scheme, verification of operating loads, tests on the materials with which the structures are made, etc.
Therefore it is evident that the concept of safety is a lot relative, that finding is confirmed from the same norms, when they extrapolate cultural goods from this obligation, except for specific situations relating to cultural heritage, which frankly leaves us very perplexed.
Indeed it is absurd that places very attended precisely to attract the public by virtue of their cultural value, they can also avoid reaching the minimum value of 0.6 required by the same law.
The reasons why the buildings historians in masonry, they are more complex to implement their seismic improvement, they are different, among main I highlight the difficulty to locate with precision the real initial structural scheme, given the inevitable changes that these buildings have often undergone over the years.
Study the structure of the more complex elements
Think of the difficulty of obtaining an adequate level of knowledge of a part of a masonry building, inserted inside a aggregate urban, with parts interconnected with other adjacent buildings.
As is now evident, carrying out a seismic improvement intervention, especially in old buildings, represents a burden not only for those who have to bear the expense, given the difficulty of organizing a construction site that allows easy operation, but mainly for the designer, who, in order to act with serenity, needs to reach the right level of knowledge of the building.
Knowledge many times masked, due to previous interventions carried out for other purposes, such as the bad practice of creating barriers rising damp, obtained by cutting the load-bearing walls horizontally, or eliminating load-bearing walls from the original scheme, etc.
In conclusion, it must be borne in mind that the satisfaction of that seismic index cited by the standards is not enough, to ensure adequate safety of the building, it is in fact necessary to have specific knowledge about the materials and their mechanical properties, the analysis of the geometry and construction details, as well as that of the possible presence of a cracking and deformation pattern of the building.
The experience of the person who has the task of verifying these elements is essential to be able to really prepare an effective seismic improvement intervention.
Source: LAVORINCASA.it by www.lavorincasa.it.
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