Seismic improvement techniques
Unlike local interventions, the seismic improvement techniques they must intervene directly on the structural skeleton and therefore they may result more invasive in the construction phase because the load-bearing structures must be exposed by removing plaster and coverings, making the real estate unit even partially uninhabitable for the duration of the intervention.
In recent years of Superbonus110%, various types of have entered the market “seismic coats” which combine the triple advantage of insulating, improving seismic safety and also without having to interrupt the internal functionality of the house because you only work on the outside. The seismic coat technology involves a formwork, which is the insulating material, laid in adherence to the building: the central cavity, which is the heart of the seismic-resistant wall, is then filled, on site, with a concrete pour (Fig. 1a).
However, these are recent technical solutions whose effectiveness must be assessed on a case-by-case basis and above all depends on the connection with the original structural skeleton of the building and therefore what type of structural collaboration is triggered during the earthquake, also in relation to a greater contribution of rigidity and seismic masses offered by the external reinforced concrete crust compared to the original configuration of the building.
It is in fact necessary to remember that for interventions classified as seismic improvement it is analysis and numerical modeling are mandatory of the entire building, comparing the actual state with the projected state. A similar solution is that of the external exoskeletons with steel profileswhich although it may be more invasive from an aesthetic point of view (but still adaptable with an appropriate architectural project), is certainly more tested (fig. 1b).
Differently, the traditional techniques of consolidation of reinforced concrete frames work with materials directly applied to pillars and beams with possible and temporary inconveniences for the functionality of the internal environments, but with solutions already widely tested and of certain numerical evaluation.
A solution applicable to reinforced concrete pillars consists in the so-called “armored jacket” (Fig. 2a), if the pillar requires shear or bending reinforcement: it is possible to apply a reinforced cement crust 8-10 cm thick with electro-welded mesh (or with additional bars) and appropriately connected transversely to the meshes of the other sides. A sort of “widespread hooping” of the pillar.
An alternative to the jacket is the caulking with angles (Fig. 2b), with declared visual impact. However, if the reinforcement needs are greater, modern composite material fabrics are certainly more adaptable, especially for the consolidation of nodes. The FRP strips (Fig. 2c) can be applied by gluing with epoxy resins.
In the beams the bands they will be applied in the areas of maximum tensile stress for bending, with intrados and/or extrados application depending on the moment diagram. They can also wrap the perimeter of the beam in the areas of greatest shear stress, or with a constant pitch along the entire span of the beam if the lack of shear reinforcement is widespread. For the pillars, depending on the stress requirements, the bands can be applied along the vertical development to increase the resistance to compressive bending and horizontally around the perimeter of the pillar, with an adequate pitch, for shear reinforcement.
With the same application they can be used for confine the beam-column nodes and ensure the resistance hierarchy of the reinforced concrete frame In the seismic field, FRP strips have the advantage of not providing additional seismic masses, as instead happens with other intervention techniques.
As with any project, the chosen intervention technology must be the one most compatible solution with the building context and with the level of seismic safety that one wishes to achieve.
