Safety measures for unsafe structures or buildings affected by earthquakes

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Safety measures for unsafe structures or buildings affected by earthquakes

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The need of taking control measures for masonry buildings which are at risk of collapse due to earthquakes, subsidence, hazards or building mistakes, requires  simple and urgent actions, yet of reduced risk for the operators in its execution.

Protection procedures for buildings are generally performed using provisionally wooden or metal shoring. In some cases of collapse, “FRP of SRG measures” (*) avoid the presumable collapse of the building, operating in a secure mood and carrying on works for a long dated security.

The installation of bandages or external hoops with FRP or SRG represents an effective alternative to conventional shoring, when referring to kinematic mechanisms of collapse due to the tilting of the walls out of the plane (the most frequent in masonry buildings with projecting elements).

Hereinafter, some case studies and experiences of this type of intervention will be examined and illustrated.

(*) Fiber Reinforced Polymer

SAFETY MEASURES FOR UNSAFE STRUCTURES: the case of Umbria-Marche earthquake

Following the seismic disaster of September 1997, few buildings were seriously damaged constituting a clear danger for public viability. To prevent from this, Regione Umbria has designed a series of prevention plans in order to restore safety conditions, with two main guides:

– The demolition of unsafe buildings (more invasive) and the management of provisional works to secure architectural and artistic relevant buildings likely to collapse. These provisional works were characterized by rapidity of execution, as well as the possibility of removing provisional work for the final restoration.

For some types of instability, double shell carbon bands -30 cm high- were used in order to discard collapse possibility of unsafe parts. The use of FRP materials is excellent when buildings, subject to the pushing action of covers, were about to collapse. The disposition of sleeves allows balancing the push of the covering structures, redistributing the strength along the main walls.

 

 

Those mentioned options and the materials used permitted: first, the rapidity of action that allowed solving immediately a hazard condition and second, but not less important, the fact that these interventions were permanent, which means only advantages for the building property and represents no contraindications as the aesthetic and architectural aspects are concerned.

The definitive allocation under the plaster will permit the removal of traces of the works performed. The ability of working outside is a great advantage because there is no need of accessing the interior of damaged buildings; another advantage is the bands adaptability to irregular shape profiles, overcoming obstacles as gutter channels, electrical wires…etc.

This technology avoids the risk of overturning collapse of slender elements of the structure, as for example chimneys or belfries, very unstable in seismic incidents.

The final covering with quartz sand protects from ultraviolet action. Please note that this intervention does not request any maintenance or stringing seasonal phases, as it is in the case of external metal cables sensitive to the variation of temperature. SRG products constitute strong innovation in the market and increase the potential of an intervention with composites.

SRG composites, with difference from the FRP, allow a pretension operation of the bandage through a tightening device.  This active operation option increases level of security in the intervention area. The active thrust allows a resistant strengthening at a first step with no need of further actions against deformation.

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CONCLUSIONS

The use of composites, either FRP or SRG, represents objective advantages compare to traditional techniques as metal wooden props, as follows:

  1. Budget;
  2. Rapidity of installation;
  3. Execution of the operation from outside of the structure, with no need of entering the unsafe building;
  4. Easy and simple transport of necessary materials to the consolidation; easy accessibility even in difficult access areas by using baskets of elevating machines;
  5. Capacity to adapt the intervention to particular conditions as presence of electric wires or rain gutters;
  6. Compare to traditional shoring, they do not clutter public roads; thickness near zero;
  7. They are fully reversible, key aspect in monumental value buildings;
  8. They are definitive works and represent a saving compare to throwaway works as wooden shoring;
  9. In the case of SRG composites, there is an option of applying active intervention through pretension;
  10. No decay over time if protected from UV RAYS;
  11. Not sensitive to temperature or humidity conditions;

TYPES OF OPERATION SCHEMES

Below are methods of placement of bandage intervention in structures with FRP/SRG composites, when seismic events occur. This is based on the standards “Guidelines for the evaluation and reduction of seismic risk of cultural heritage with regards to technical standards in construction” – Attached text to Opinion n.66 from “Assamblea Generale del Consiglio Superiore dei LL.PP. reso nella seduta del 21 Luglio 2006”

Messa-in-sicurezza-con-FRP-10

We thank Eng. Riccardo Vetturini from Foligno (PG) for his contribution in drawing up the article in the seismic risk protection section.

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2017-12-15T05:34:48+00:00
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