PSI - Issue 57

Jeroen Van Wittenberghe et al. / Procedia Structural Integrity 57 (2024) 95–103 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 3: (left) instrumented single girder crane with 3 optical fibre sensing lines (right) position of the strain FBG sensors.

The bottom flange of the crane girder is instrumented with 4 optical fibre lines with FBG sensors. These are visible on the left picture in Fig. 3. The two outer fibre lines (referred to as North and South) are located under the vertical web plates of the crane main girder and contain 9 FBG strain sensors, each equidistantly distributed over the girder length. The 2 central optical fibre includes 2 FBG temperature sensors. 3.1.1. FBG strain monitoring system The FBG strain sensors measure longitudinal strain (direction z, Fig. 7). Therefore, it is possible to evaluate the structural response of the crane, which is impacted by various factors, including trolley position, hook load, hoisting speed, and load swing. Fig. 4 shows strains obtained by the nine FBG sensors of the north fibre when the trolley was moved from the left girder extremity to the opposite extremity, carrying a load of 9 tons. Maximum strain reading is obtained by sensor five (located at girder mid-length, Fig. 3) when the trolley passes most close to it. Two peaks can be observed in each sensor reading which are associated with the trolley wheel. Due to the hook position, the load is not evenly distributed over the two trolley wheel pairs. Therefore, the strain peaks have different heights.

Fig. 4: FBG strains for the north fibre line when the trolley is moved along the girder. Logically, as the trolley approaches the sensor position, the strain readings increase. The utilization of two parallel FBG strain lines allows the detection of girder horizontal bending by comparing the strain readings of the two strain fibre lines. This is exemplified in Fig. 5, which shows strain readings of sensors #5 (Fig. 3) in both fibre lines (north and south) when a 1 ton load was swang perpendicular to the girder. The swing of