THE stone balconies They are elements characterizing the historical construction and the architectural design of the facades of many buildings. Are normally made by Lapidee slabs resting on a similar material shelves embedded on the wall walls. In the most recurring dimensions, the overhang of the shelves is of the maximum order of 100 cm, while its part of the interlocking inside the walls must be commensurate with the overhang and in any case around 40-50 cm depending on the thickness of the walls.
The degree of interlocking of the shelves It is also guaranteed by the homogeneous texture and the above weight of the walls. The corporation of the shelves is in the order of 150-200 cm, corresponding to the support light of the walking slabs of the order of the order of about 8 cm, with considerable weight on the shelves.
Risks and critical issues of stone balconies
Over time, if not carefully maintained and inspected, the stone balconies are potential risk factors for public safety.
Not infrequently we read in the chronicles news of sudden collapsesthe last of which happened on 9 December in Rus Ferrarese during a school visit inside a private historic building. In that dramatic event the schoolchild had faced the balcony and then returned inside the building. On the balcony only the tourist guide and the professor of the class remained, when the stone slab suddenly sold them to fall to the ground from the first floor with serious injuries, which unfortunately were fatal to the young teacher who died a few days later.
The event highlighted the fragile behavior of the stone which determines a sudden breakage, without giving premonitory signals.
The mechanical characteristics of the stone
There stone It is such a varied material in its composition from make static checks complex.
The mechanical characteristics They are very heterogeneous according to the type of rock, origin and deception plans inside. The same stone solicited in an orthogonal direction to the deception plans will have different mechanical resistances if solicited in parallel to the aforementioned plans. In the scientific literature there are intervals of resistance values variable between a minimum and a maximum with a certain degree of randomness.
For this reason, at least in the new designit is important to have from the suppliers more detailed and certified values Regarding mechanical resistances, which will be able to diversify according to the draw of extraction and processes. The extracted material can also be subject to Small hidden defects: In fact, they are not rare breakage of shelves in the operating phase also on new buildings. For this reason, it is very important to invest in the characterization of extraction materials through preliminary laboratory tests, to increase the statistical relevance of the resistance values necessary for the calculation checks to the limit states.
Degradation and environmental factors
On Existing balconies increases theuncertainty of real mechanical performance because in addition to have no certification on the original materialif not with load tests in situ, it is also necessary to take into account the level of Materico degradation that the stone element has undergone over time in the absence of maintenance. The stone elements of the balconies are constantly subject to frost cycles, rain actions, biological patients which reduce resistance to non -table values and contribute over time to any and sudden structural collapses.
Diagnosis and safety tests
To undertake Security checks Some need diagnostic testsof qualitative type, capable of offering an evaluation first of all on the State of degradation and integrity of the stone element. The ultrasound tests They represent a valid investigation phase to intercept any cricche or cracks not visible outside inside the stone.
The technician may compare the ultrasonic speed of the type of stone present in the scientific literature with that detected in situ, evaluating lower values as signs of the material or structural degradation e as a result An appropriate safety coefficient that takes into account the performance degradation.
Structural reinforcement interventions
Historically the shelves and balconies are reinforced with metal profiles of the IPE or similar sectionpositioned below the trampling surface and stuck in the walls in support of the shelves (positioned by their side) or of the slabs themselves (in the middle or where they are crapped). As invasive as it may seem, now for his reversibility and ease of execution is the most historically performed intervention in the past and therefore already characterizing the facades of the buildings for how we see them today. Also for this reason it is a type of intervention accepted by the Superintendencies in the context of the bound construction.
Being recurring and potentially dangerous collapsesis a duty Invest in the diagnosis phase, verification and maintenance of stone balconiesrelying on a structure that will evaluate the possible need for static reinforcements to reduce risks on public and private safety.
