 So, hello, good afternoon everyone. My name is Antonio Barrios and I'm currently working towards my PhD at Barcelona Tech in Spain under the supervision of Professor Casas. And today I'm mostly talking about the exact applications that we did in our research group back in Barcelona using optical backscatter of phytometry or OBR based distributed optical fiber sensors. And I must say that I'm actually in the end of my first year and most of the work that I'm going to present was done before I arrived to Barcelona so bear with me as I try to properly present these applications. So just a quick overview of my presentation. First I will introduce briefly the role of fiber optic sensors on SHM. Then I will specifically speak about the distributed form of these fiber sensors. Then I will showcase all the applications that we did using these types of sensors back in Barcelona. And then I will conclude with some remarks about our examples and applications. So in a simple way fiber optic sensors present a lot of advantages when compared with the use of more traditional and electric sensors. Some of them are represented here but I want to pinpoint for instance the fact that they are immune from electromagnetic interferences. So they allow us to obtain very noise free data and also that they are very small and lightweight so they are very easy to install and operate. And there are several different ways of categorizing fiber optic sensors but for the purpose of this presentation we decided to sort them out on these three different categories grading based sensors, interferometric sensors and the distributed sensors. So the distributed sensors are the ones that I am going to speak about here and this happens we think these are very good type of sensors because for the additional advantages that I showcase on the previous slide here an additional advantage is the fact that virtually every cross section of the structural element that is being monitored is being monitored so all the possible damage that is going to occur in this case cracks are going to be covered by the sensor and otherwise that would be not possible with the use of discrete or point sensors. Another additional advantage is when monitoring structural elements specifically for latch the structures the number of sensors that can rapidly increase and with the number of required connections and with the use of doffs of the distributed fiber sensors we can use just one optical fiber, one sensor and with it only one connection cable making the all the monitoring system more easily done. So these sensors work by the interaction between the light source and the optical sensor that this phenomenon is called scattering and it occurs in all directions but it is the back scattering that we are mostly interested in about. The back scattering provides three components and these three components are the Rayleigh component, the Brillian component and the Raman component. There are different ways of using these components to obtain the changes in the structural element that we want. In the time domain we have BLTDR and the BLTDA that they are being the most used and successful techniques applied both based on the Brillian component and they are characterized by providing long range sensing and but however they present a very low special resolution around one meter which is insufficient for crack detection or damage attraction. On the other hand we have in the frequency domain the optical back scatter of the FETOMETRY the Rayleigh based of OFDR that uses the Rayleigh component through the use of this swept wavelength interferometry that provides us a very high special resolution as high as one millimeter for the reading of strain and temperature and this technique is characterized by having a short range sensing but providing a very high special solution that is good for damage detection. And this I forgot to mention this was a technique that we used in all our applications that I'm going to showcase now. So this was the first application that we did back in our laboratory in Barcelona. This was done in 2009. So the main goal here was to assess and study how the sensor was going to perform when used on this concrete slab and also to see if it was able to with the use of this monitoring system to detect and locate the appearance of cracks on these structures. So the four different stretches of this optical fiber sensors were implemented here two on the top side slab and two on the bottom side slab. Here we can see some pictures of this experiment. This was a small slab 5.6 meters long, 1.6 meters wide with the thickness of 0.285. A simple supported slab and the load was implied with the use of this MTS actuator in the middle of the span. So we obtained these graphs with results where we can see the strain plotted against the length of the fiber for different stretches. We analyzed each stretch separately. Here we obtained the ultimate load of the slab of 255.15 kilonewtons. And as you can see, we were able to obtain continuous records for different levels continuous, not only in time but also in space. And as you can see, the peaks that we obtained with these graphs, they present a very good correlation with the visual of certain cracks that were appearing on the slab. So we were able to not only detect but localize the cracks that were appearing in the slab with the use of these sensors. And you can also observe that even for high load levels, the fiber was performing very well and without breaking. And afterwards, this was more recently, there was an algorithm that was developed in order to try to quantify the damage. So for these, we tried to calculate the average crack width in specific zones. We used the strain that we obtained using the OBR sensor. By equalizing these two expressions, we were able to solve it by the sum of the total width of the cracks. And then, dividing by the total number of cracks, we were able to obtain this average crack width. And as you can see here, comparing with the electrical sensors, we have a very good agreement with the stretches that we have with our OBR sensors and the means of these electrical sensors, which is very encouraged and validates the use of this algorithm. More recently, we tried to apply the same sensor for the monitoring and the detection of the shear crack pattern on partially pre-stressed concrete beams or PPC beams. This was done in conjunction with another group in our university. Partially pre-stressed concrete beams, especially, they are designed to allow the crack under service loading. So the use of monitoring systems for the control of cracking is especially important in this case. And the beam was divided into a bending test span and the shear test span. We only instrumented the shear test span and that's what I'm going to speak about here. So we proposed this grid to monitor the crack propagation information in these beams. We proposed two different beams, the BMI-1, where we used two different optical fibers, one that was concentrated in measuring longitudinal strains and the second one for vertical strains. On the second one, in BMI-2, we just used one longer cable that will conform the similar 2D grid for the detection of this crack propagation. Here we see an image of beam I2 with the cable glued to the surface of the beam and here on the right, you can see that we also used a strain rosette with LVDTs for the monitoring for comparison purposes with the results of the OBR sensor. So we analyzed each stretch separately and after analyzing each stretch, we were able and converting all the stretches for a local coordinate system that corresponded with our 2D grid. We were able to form these 2D graphs that have the maps of the shear crack propagation information and as you can see they provide a very good agreement with the visual observed ones with photographic evidence. In the same way that we did with the concrete slab, we also tried to apply this algorithm in the different ways here to calculate the shear crack width and average crack width. I'm not going into a lot of detail here. This is part of the work of my colleague Gerardo Rodriguez who's finishing his PhD. So in the end, I have the references and if you want, you can look up and see more about this. Again, comparing with the more traditional sensors with the LVDTs, we see a very good agreement with the obtained calculator crack width with the OBR and the one obtained with the other sensors. Now going to real world applications. This was the first application that we had on a real world structure in these viaducts on a highway near Barcelona in Spain. It's a 125 meter long bridge that has a deck with 14 meters wide with pre-stressed box beams over five spans that are supported in double piles. And here we used three different optical fibers, two 25 meter long fibers allocated longitudinally to the structure and another one, 50 meter long cable that was allocated perpendicular to the structure in three different cross sections. And here the test was divided between two parts. The first one was a moving load track of 400 kilonewtons that was passing in the second one on the track being stopped on the middle of the bridge with the normal passing of vehicles. And the main goal was to assess and study the feasibility of the use of these sensors on a real world structure and also to compare with other used sensors that were allocated in the structure for initial load tests. So here we can see, for example, in the first part of the test, the obtained strain data on fiber F02, the one that was allocated longitudinally. Here we can see when the track was going in one quarter of the span, we have these distributed off-strain. Then after the test was completed and the removing of the track, we obtained these horizontal strain that was more or less as we expected. On the second part, as I said, the track was stopped on the middle of the span and there was the normal traffic passing by the bridge. And here we can see after 10 minutes of stabilizing the system, we obtained this distribution of strain as we expected with the higher strain in the middle span. So afterwards we tried to calculate the displacement and we were able to calculate the displacement of 3.45 millimeters, the deflection at mid-span with the OBR data. And comparing with the experimental obtained one of 3.71 millimeters, we concluded it presents a very good agreement. Another bridge that was more recently last year in Barcelona, this Sarajevo viaduct, this viaduct is located in one of the main entrances of Barcelona, so there's a lot of traffic passing under by. Here the bridge authorities decided to enlarge the deck, so during this process they asked us to allocate these distributed optical fiber sensors inside the beams. So we used two different optical fibers, DOF 1 and DOF 2 that are showcased here. And this process was done through several months from June last year until more or less February of this year. And as you can see, you can see an evolution of the strains for the different measurements, which was most important was the fact that we could obtain the stress increases and variations with the use of these sensors. And we were able to conclude that there were not induced changes to the structural area that were significant. So the use of these sensors allowed us to assess the safety of this process. Also, this concrete cooling tower in the north of Spain near Barcelona was also instrumented with the use of OBR sensors. Here two main vertical cracks had appeared, so we decided to use the sensors to start the behavior before and after crack repair. And this is a 120 meter high structure. So before allocating the sensors, there was a 3D finite element model that was developed in order to help us decide where we should put the sensors. And it was here in the middle next to the main area of the cracks. So this is one of the examples of the strain rings that we got from the outside surface tower. Here we can see from the inside surface tower. I just would like to pin points here that we can see different types of peaks. And we should be very careful because the concrete presents some roughness that should be taken care in account when analyzing these data. For example, these small peaks, they represent that roughness of the concrete and should not be taken account into cracks. On the other side, these higher peaks that they are dynamic and they change with the time. They are representative of the cracks and the damage formation in this structure. In the same way that I said about the previous bridge in the above the highway, we also perform an integration and obtain the deflection at mid-span using the OBR data. And it was able to see that it agreed very well with the 3D finite element model and with the other electrical sensors. So the use of this sensor allowed for the increase of the lifetime of this cooling tower. And finally, this historical monument in Barcelona, this UNESCO World Heritage Site, was also a target of our application for the OBR sensor by our group. Here, there was some kind of cause of concern because two columns presented some serious cracking. So it was decided to replace those two columns. So we allocated the fiber sensors on the top of the floor during the removal and replacement of these columns. Here, you can see where we allocated the optical fiber sensor. And with it, we obtained these type of measurements. The first column was replaced on the 1st of February. That's why we had three measurements here. Here, it's the old data. So in order to be more clear, we should zoom the information here for a 10 centimeter length. And here, you can see with more precision what was happening. We see that during the first reading that is a calibration, it's around 20 microstrains. And then with the replacement of the first column, there was an increase of strain of between 20 and 14 microstrains. And the highest strain that was achieved was 100. But since we have to subtract the initial calibration, we would say that the maximum increase of strain was of 80 microstrains. Then we can see that for the last reading, the structure is indeed regaining stiffness. So it's as we were expecting. So I'm reaching my conclusions. And with these examples, we saw that the OBR sensor is a very promising technology for SAGM, since it allows for continuous not only in time, but also in space of strain and temperature measurements. With these experiments, the main objectives were to assess the performance of these sensors, both in laboratory and real-world conditions. We saw with these examples a very good performance of this technique, since it showed a very good agreement and good correlation with the use of other conventional sensors. One thing that we also concluded is that the use of a correct bounding agent and the smoothing of the concrete surface before applying the sensor is very important in these types of applications. Also, the OBR sensors, they present a very good performance for either low levels or low levels close to the failure of concrete. And finally, since this is a workshop that tries to quantify the value of SHM, the economic impact of these sensors, although they present a very high initial investment especially on the acquisition system, we think that they present a very important economical saving when comparing with other monitoring techniques, since there's no other technique that is able to provide the same information with the same number of monitored points. So here are the references if you want to look further up about these applications. And thank you very much. If you have any question, please feel free.