Category: PROJECTS

In countries with medium to high seismic risk, a seismic vulnerability assessment is needed. Many infrastructures such as hospitals, schools, bridges or viaducts need urgent and detailed assessments to determine their actual state of preservation.

As recent tragic events have shown, earthquakes and wear and tear are the two of the biggest threats to countries structures and infrastructure and to people’s lives.

What is the ATLANTE Project

The ATLANTE project of the Tuscany Region concerns the development of an innovative prototype for the monitoring of large structures (buildings, bridges, artifacts, …) that uses the technique of Mid Infrared Digital Holography (MIR DH) and represents real progress in the methods of structural diagnostics. Lunitek is the sole technical/scientific contact for the project, which is supported by Campera Electronic Systems (CES). The technique was developed by the National Institute of Optics of the CNR (CNR-INO) in Florence together with the Department of Earth Science of the University of Florence (UniFI-DST). Prela Perparim LP and DGNET srl are also participating in the project, with Commit Software as consultants.

Comparison between seismic and MIR DH techniques

The limits of the seismic method

Currently, seismic measurements are used to determine the health status of structures and their reference parameters. The seismic technique, based essentially on the use of accelerometers and/or seismometers to be positioned inside the structure, is rather invasive and expensive in terms of time and human resources and it’s therefore difficult to use on a large scale. With this technique, moreover, it’s not possible to obtain information on possible drifts of the structure such as, for example, the slow subsidence of a wall, the buckling of a city wall or the deformation under load of an attic or a bridge. Finally, the seismic technique is not applicable in all those situations where it’s not possible to put the device on the surface to be monitored (vertical surfaces, crumbling structures, architectural elements that are difficult to access, …).

Advantages of the MIR DH technique

The holographic technique is suitable for monitoring most of the existing structures and allows you to obtain the same information as the seismic technique, in a considerably shorter time, with a more limited use of human resources and remotely, i.e. remaining outside the examined structure, and also allows to monitor all the buildings in an entire urban area.

The holographic technique also allows the user to monitor large surfaces of the structure, obtaining a real map of deformations/displacements of the surface under examination. Finally, unlike the seismic technique, the holographic technique is also able to follow drift motions of the examined structure and to predict the dynamic response of the structure to external stresses, whether environmental or related to human activity.

These features significantly expand the field of application of this technique to structural engineering, seismic vulnerability and cultural heritage conservation, allowing non-invasive monitoring of environmental deterioration and the ageing process of historical monuments and artistic sites.

• The technique is mainly indicated in the prevention phase but can also be used in the post-seismic event phase to determine which of the surviving buildings are really safe. The ability to operate remotely and with very short measurement times makes the technique very well suited to large-scale use, allowing the monitoring of entire urban areas.

The technique can also be used for non-destructive tests necessary for the certification of viability of buildings and infrastructures and is perfectly suited to the monitoring of cultural heritage (statues, frescoes, etc.) and, in general, of all those architectural-constructive elements (columns, terraces, chimneys, …) for which it is interesting to provide both static (under load) and dynamic characterization.

It is now generally recognized that the systematic monitoring of most existing buildings and infrastructures is necessary in order to provide the real estate assets with a kind of ‘structural identity card’.

The technique based on MIR DH represents a revolutionary advance in the field of dynamic characterization of large structures to assess their state of health and/or degree of seismic vulnerability and, therefore, establish complete and correct prevention strategies.

The total funding provided by the Tuscany Region amounts to € 587,780.49.

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We live near Carrara, the town where the world’s most popular and most sold marble is extracted, Carrara marble.
Marble quarries are as impressive and scenic as they are dangerous.
Indeed, they are often the place of fatal accidents.
This is why the safety of marble quarry workers is a priority for the Tuscany Region.

What is MONFRON?

MONFRON is the acronym of “Monitoraggio Fronte di cava” which translates as “Front of Quarry Monitoring system”.

This is a large project, which was presented to the Tuscany Region in 2017. The project was funded in January 2018 and sees Lunitek as the lead company, together with Santucci Graniti Srl, the quarry owner, and ApiAn the rock climbing organisation.

The project idea is to prevent the sudden and unexpected rockslide falling on quarry workers. Prevention cannot be carried out using traditional instruments for geophysicist (accelerometers, velocimeters, GNSS or laser scanners) because, by the time these types of systems trigger an alert, in most cases, it is already too late, and the rockslide cannot be stopped.

Lunitek presented a proposal for monitoring by employing an Acoustic Emission (AE) technique over a period of 18 months.

How Acoustic Emission technique works?

Acoustic Emission (AE) is the phenomenon of radiating acoustic waves in solids that occurs when a material undergoes irreversible changes in its internal structure. This is due to the rapid release of localized stress energy. Acoustic Emissions can be detected in a frequency range from few KHz up to 100Mhz, but most of the released energy is from 1KHz to 1 MHz.

Thanks to AE technique it is possible to localize the source of the emitting event.

Lunitek has been working in this field in close collaboration with the Polytechnic University of Turin since 2008.

Professors from Structural Department (Carpinteri, Lacidogna, Bertetto, Niccolini) worked with us to transfer their know-how and to design a cutting-edge technology product.

All these efforts have led to the AEmission an 8-channel fast-sampling datalogger with a parametric processing of the acquired data.

AEmission

AEmission is an eight channel datalogger for acoustic emission waves.

It can sample data at 1.25MS/s@18bit or at 10MS/s@16bit.

Piezo-ceramic sensors can be connected directly to the instrument without any external conditioner.

An internal high-performance FPGA performs real-time analysis of the data stream coming from the ADCs and extracts the parametric data.

Why Acoustic Emission is the right tecnique?
Acoustic Emission (AE) is the only technology that can spot a potential cracking fractures inside a solid.
The idea is to trigger an alert when abnormal conditions are detected on the data processing.

Since we are talking of an experimental investigation, the site is also monitored with other techniques:

• ATLAS with an external FBA accelerometer on the quarry front 1.
• TRITON FBA accelerometer outside the monitored site.
• A meteorological station.
• A thermocouples array installed on the quarry front 2.

All this information can help to discern false events from real cracking events.

The system has been deployed as shown in the below pictures

Statistic analysis of B-value and βt parameter

On the below picture some of the monitoring fundamental parameters. In particular it is possible to notice a reduction of the fundamental parameters related to the damage evolution (b-value). It is also possible to notice the appearance of some points of acoustic emission locate on the monitoring front n.2

Result and conclusions

Based on the data highlighted by the localization technique and in correlation with the values ​​assumed by the critical parameter of the b-value, it is possible to consider the areas corresponding to sensors 1-7 and 2-4 as critical areas. In these areas, in the central phase of monitoring, the parameters that mark the evolution of the damage highlighted sub-periods with a localized increase of the damage.

The total amount of the founding received from the Tuscany Region was 282.000€

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