PSI - Issue 64

7

Bartosz Piątek et al. / Procedia Structural Integrity 64 (2024) 1581–1588 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1587

Fig. 8. Comparison of strain profiles over length measured by monolithic sensors ED2 inside the duct under force of 350 kN.

3.5. Displacements Various methods can be used to calculate displacements from the DFOS-based strains measured at different, but well-known locations within the element of interest (Kulpa et al. (2021)). One of them, chosen for this study, is to install specially designed DFO displacement sensors (3D). Their internal design includes a highly elastic composite core and a flat cross-section with four optical fibers precisely arranged in the lower and upper beams’ surfaces. The curvatures and displacements in 3D space can then be obtained directly from the measured strain profiles (Bednarski et al. (2021)). The sensors can be either embedded in the concrete or bonded to the beams’ surface. The precision of the installation process, excluding any waviness or twisting, is very important to obtain the required accuracy. In this context, installation on the surface provides the highest possible accuracy. Exemplary results of vertical displacement profiles obtained using 3D sensors located in various places of the PT1 beam (one surface 3DE and two embedded 3DS and 3DD) under load of 500 kN are presented in Fig. 9. The simply supported static scheme was assumed for calculations with zero vertical displacements at the supports. Deflections calculated using data from DFOS sensors were compared against reference values from conventional LVDT transducers positioned along the length of the beam, demonstrating excellent agreement (table 1). Such consistency allows the proposed measurement approach to be considered effective and sufficient to assess deflections in practical applications.

Fig. 9. Comparison of displacement profiles from monolithic sensors 3DE, 3DS and 3DD under load of 500 kN with LVDT spot readings.

Table 1. Displacements measured by DFOS sensor (3DE) and spot LVDT transducers.

LVDT 2

LVDT 3

LVDT 4

LVDT 5

LVDT 6

LVDT 7

LVDT 8

Load phase

Force [kN]

Location:

Mean

1.75 m

2.45 m

3.15 m

3.85 m

4.55 m

5.25 m

5.95 m

LVDT (mm) 3DE (mm)

-16.8 -16.5

-23.7 -23.2

-28.2 -28.1

-29.7 -29.9

-27.8 -28.4

-23.3 -23.6

-16.9 -16.9

-23.8 mm -23.8 mm

19

500

Δ (mm)

0.3

0.5

0.2

-0.1

-0.5

-0.3

0.0 0.3

0.0 mm

Δ %

-2.0

-2.1

-0.5

0.4

1.9

1.3

-0.1%