PSI - Issue 72

Andrey Yu. Fedorov et al. / Procedia Structural Integrity 72 (2025) 453–457

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Laser position sensors were applied to the bottom of the vessel and the upper free surface of the concrete mixture to monitor sample shrinkage. Shrinkage monitoring allows determination of the time interval after which the sample geometry remains unchanged. This interval was approximately 200 hours. Fig. 2 shows the evolution of technolog ical strains over this ∼ 200-hour period. Technological strains began to appear after the completion of the shrinkage process. The level of these strains increased with distance from the sample surface. The measurement results provide qualitative and quantitative insights into the evolution of technological strains within the material volume and enable more reliable estimates of the mechanical state of concrete structures.

Fig. 2. Registration of technological strains in the sample.

To assess the reliability of strain measurements by FOS embedded in concrete, experiments were performed by applying uniform pressure across the sample’s upper surface. Simultaneously, strain measurements were conducted using a resistive strain gauge mounted on the side surface of the sample. The di ff erence between the strain measure ments from this gauge and the FOS at strain levels up to 300 µε was no more than 12%, confirming the quantitative accuracy of the FOS measurements. 3. Algorithm and results of the defect detection experiment The algorithm for detecting defects based on strain measurement results relies on two key principles. First, strain has a linear dependence on external influences. Second, the implemented variants of external influences differ from each other by a constant multiplier. To detect defects, a set of sensors that measure strain εi (i = 1, 2, ..., n) at a given number of n points is used. For each measurement time tm (m = 1, 2, 3, ...) of the strain measurement n(n − 1)/2, relative values can be obtained:

t m

i  

t

m

, 1,2,..., , i 

1,...,

k

n j i

n

(1)



 

ij

t m j

When a defect appears and develops in the vicinity of the sensor i = s , the following relations change: t m s  t m j  , j = s + 1, s + 2, ..., n and t m i  , t m s  , j = 1, 2, ..., s − 1. Thus, changes in the observed values t m j  , t m j  allow for conclusions about the appearance and development of defects, as well as about the area of their occurrence. In the practical implementation of the considered technique, a limited number of sensors is used. Based on engi neering experience or the results of numerical modeling, it is proposed to place sensors in areas of stress concentration, where the probability of a defect (destruction) is naturally high, and in areas without stress concentration.