Applications of DOFS in Civil Engineering

Hello everyone!

Hope you all had a great Easter. Now it's time to get to know a little more about Distributed Fiber Optic Sensors (DOFS).

As I mentioned last month, in this post I will talk a little bit about some recent applications of DOFS in civil engineering structures, focusing on the work being done by our research group at Universitat Politècnica de Catalunya (UPC).

The great majority of photonic sensing technology applied in the area of civil engineering is constituted by discrete sensors such as the Fiber Bragg Gratings (FBG). This topic has been extensively discussed in different publications in the past decades. 

Nowadays, DOFS sensors are an attractive technology that offers superior performances and advantages when compared with more conventional sensors applied in Structural Health Monitoring (SHM) practice, as explained in the previous posts. Despite their apparently high cost, they are ideal for applications where reliability in challenging environments is essential. Furthermore, they provide lower installation and maintenance costs.

However, this is still a recent and developing technology as it can be perceived by the relatively few number of DOFS applications in SHM projects. Notwithstanding, some different DOFS applications were made in the last two decades in various and very distinct civil engineering structures such as bridges, dams, tunnels, pipelines and slopes. Also, a great load of work was made, with the goal of improving these sensors capabilities by executing different laboratory experiments.

The ability to cover long distances, perform distributed measurements (both in space and time), immunity to electromagnetic interference and endurance, are some of the advantages of the DOFS over traditional discrete measuring sensors. For these reasons, these sensors have been initially and mostly instrumented in large structural systems. As discussed in the previous post, the Brillouin optical time domain analysis (BOTDR) has been the most applied technique of DOFS based sensors due to their wide range of measurement capability. In order to get to know with more detail examples of the application of this technique on bridges monitoring, for example, the reading of the following documents is advised: (Bastianini et al 2005a), (Bastianini et al 2005b), (Minardo et al 2012a), (Minardo et al 2012b), (Glisic et al 2011), (Glisic et al 2013).

When a better spatial resolution is necessary (for crack detection for example) in a relatively cost-effective way, the most sought-out technique is the Rayleigh based optical frequency reflectometry (OFDR) or as is also known, optical backscattered reflectometer (OBR) and this is the equipment that we mostly have been working with at UPC - Barcelonatech.

One of the first conducted experiments with the goal of exploring the capabilities of crack detection in concrete elements was conducted by Villalba & Casas, 2013 by instrumenting a concrete slab with OBR based DOFS that was then subjected to a load test .

Since then, various and different applications have been made by this group with engaging and promising results. From those, we can highlight the experiments done in Viaduct Road BP-1413 and a concrete cooling tower in Spain, that are described in greater detail in the following publication (Casas et al 2014).

Viaduct Road BP-1413 and Concrete Cooling Tower

Another impressive experiment was conducted in the extraordinary historical building of Hospital de la Sant Creu i Sant Pau. This building, one of the most outstanding examples of the Modernism movement in Barcelona of the beginning of the 20th Century and a UNESCO World Heritage Site. The OBR system was implemented, during the replacement of two deteriorated columns, on the adjacent upper slab where it successfully monitored the stress redistribution of this structural element due to this process.

Hospital de la Santa Creu i Sant Pau and implemented DOFS

More recently, this research group has been working on two experiments which have yet to be published. The first one is the attempt to detect and map shear induced cracks on partially prestressed concrete beams (PPC). This is of extreme relevance since that contrary to what happens with bending cracking, where the cracks appear orthogonally to the beam axis, in the case of shear action, the inclination of the cracking pattern is previously unknown and may even change depending on the prestressing force and the location along the element. For this, a two‑dimensional DOFS grid was proposed that monitored the crack initiation, location, inclination and evolution during a beam load (Rodríguez 2016).

Finally, this research group, instrumented one span of a bridge in Barcelona with a OBR system in order to monitor this structure during a deck enlargement rehabilitation. This process was conducted through several months, spanning from summer to winter, so consequently the topic of temperature influence in the measurements was a relevant issue that needed to be addressed.

Sarajevo Bridge, Barcelona

Well, I hope you have enjoyed these examples and hopefully in the future you will be able to read more about these ones and more in developing publications.

For more developments tune in again at the end of next month!

Now I have other matters to attend to :)


Greetings from Barcelona! See you guys soon!



Bibliography

Bastianini F., Corradi M., Borri A. and di Tomasso A. (2005a), "Retrofit and monitoring of an historical building using "Smart" CFRP with embedded fibre optic Brillouin sensors". Construction and Building Materials, 19, 525-535

Bastianini F., Matta, F., Galati, N., Nani A. (2005b) "A Brillouin smart FRP material and strain data post processing software for structural health monitoring through laboratory testing and field application on a highway bridge" Proc. SPIE, 5765, 600-611

Minardo A., Bernini R., Amato L. and Zeni L. (2012a), "Bridge monitoring using Brillouin fiber-optic sensors", IEEE Sensors Journal, 12(1), 145-150

Minardo A, Persichetti G, Testa G and Zeni L. (2012b), "Long term structural health monitoring by Brillouin fibre-optic sensing: a real case", Journal of Geophysics and Engineering, 9, S64-S68

Glisic B., Chen J. and Hubbell D. (2011), "Streicker Bridge: A comparison between Bragg-gratting long-gauge strain and temperature sensors and Brillouin scattering-based distributed strain and temperature sensors", Proc. of SPIE, 7981, 1-10

Glisic B., Hubbell D., Hoeg S. D. and Yao Y. (2013), "Damage detection and characterization using long-gauge and distributed fiber optic sensors", Optical Engineering, 52(8), 1-12

S. Villalba and J. R. Casas, "Application of optical fiber distributed sensing to health monitoring of concrete structures" Mech. Syst. Signal Process., vol. 39, no.1, pp. 441-451, 2013

Casas J. R., Villalba S and Villalba V. (2014) "Management and safety of existing concrete structures via optical fiber distributed sensing". Chapter of the book "Maintenance and Saftey of Aging Infrastructure". Dan M. Frangopol and Yiannis Tsompanakis, Editors. CRC Press. Taylor and Francis 

G. Rodríguez, J. R. . Casas, S. Villalba, and A. Barrias, “Monitoring of shear cracking in partially prestressed concrete beams by distributed optical fiber sensors,” in Proceedings 8th International Conference on Bridge Maintenance, Safety and Management, IABMAS 2016, 2016 (Acepted)