PSI - Issue 11

Esequiel Mesquita et al. / Procedia Structural Integrity 11 (2018) 138–144 Author name / Structural Integrity Procedia 00 (2018) 000–000

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Fig. 4- Imposed force, with the pull-out testing machine.

Figure 5 shows the results of relative displacement versus time collected by the FBG sensor and the LVDT located at the end of the bar, as present in Figure 3. The displacement curve is composed by a linear elastic phase, which moves up to the maximum relative displacements, 208.88 µm, followed by a continuous curve and an abrupt decline. As can be observed by the different pull-out curves demonstrated by Figures 5a) and 5b), the FBG sensor provide an accurate measurement of the displacements occurred at the bars surface inside the concrete, while the LVDT placed outside of the specimen presents influence of another’s factors, as concrete layer influence.

a)

b)

Fig. 5- Experimental data from pull-out testing (a) measured with the FBG sensor located inside the specimen and (b) collected by the LVDT sensor, outside the specimen.

The LVDT was placed outside the sample at opposite way of the loading cell. As expected, the relative displacement between the rebar and the concrete measured inside the specimen is inferior to the one measured outside on the force application point, but superior to the one measurement by the LVDT at the opposite face. This clearly demonstrates the need for such sensors to perform the bond-slip measurement inside the specimens. 5. Conclusions In this work, an optical fiber sensor based on an FBG for bond-slip monitoring of RC structures was tested. The results obtained showed that the Bragg grating sensor was able to characterize the bond-slip displacement in the sample tested, with a high level of sensibility to micro-displacements. The system for bond-slip monitoring proposed in this work can be applied with lower intrusiveness without the necessity of periodically removing of samples from the structure. The results, showing very different relative displacements inside and outside the specimen, clearly demonstrates the need for sensors to perform the bond-slip