Deflection determination of concrete structures using distributed long-gauge strain sensors is investigated in this paper. Firstly, the relationship between deflection and distributed long-gauge strain of concrete beams is presented, and the method is independent of external load and takes account of structural nonlinearity. The deflection distribution along the span of a beam-like structure can be predicted from strain response for the whole process of loading (elastic stage, concrete cracking stage and steel yielding stage). Secondly, experiment of a reinforced concrete beam has been conducted to verify the accuracy of the method. Experimental results show that the relative error between the estimated and actual deflection can be controlled within about 5% while the error can reach up to about 70% if structural nonlinearity is not considered. Finally, the influence of error of material parameters and sensor gauge length on deflection estimation has been analyzed. The error of concrete compression strength has a limited influence on deflection prediction while the contribution of tensile concrete should be considered before concrete cracking. The error of area of tensile bars will affect the deflection accuracy after concrete cracking.

An indirect method for monitoring dynamic deflection of beam-like structures using strain responses measured by long-gauge fiber Bragg grating (FBG) sensors is proposed in this paper. Firstly, a theoretical derivation shows that structural deflection is in direct and linear relationship to long-gauge strain. Meanwhile, the method is suitable for structures with different boundary conditions and irrelevant to external loads. Secondly, the influence of boundary conditions, load type and sensor gauge length on the method is investigated by numerical simulation. Finally, an experiment of a simply supported beam subjected to dynamic loads was designed to verify the method. Experimental results show that both deflection time-history of arbitrary points of structures and deflection distribution along structures at a certain time can be obtained with high-precision. Therefore, the method presented can be a new alternative for the deflection evaluation and maintenance of engineering structures.

Quantitative assessment of strengthened concrete structures using self-sensing fiber-reinforced polymer sheets is presented in this article. First, strain distribution along the height of a structure induced by pre-tension force (initiate state) is theoretically estimated. Second, the procedure for parameter estimation of prestressed fiber-reinforced polymer–strengthened structures under external load using measured and pre-tension force–induced strain is established, and nonlinearity caused by random cracks is considered in the method. Both local parameters (neutral axis position, bending stiffness distribution, strain distribution along the cross section, etc.) and global parameter (deflection) of structures can be accurately estimated by measured long-gauge strain responses. Finally, both prestressed fiber–reinforced polymer–strengthened and reinforced concrete beams installed with long-gauge fiber Bragg grating sensors have been experimentally investigated to prove the effectiveness of this method. Experimental results indicate that the estimated neutral axis height and local bending stiffness can reflect initiation of random cracks and deterioration process of structures under increasing external load. Meanwhile, the estimated strain along the beam height and deflection at mid-span agree well with the measured ones, which further verifies the accuracy of the estimated neutral axis position affected by randomly appeared cracks. Hence, the method can be utilized for assessment and maintenance of fiber-reinforced polymer–strengthened structures.

Long-gauge fiber optic sensors have proven to be valuable tools for structural health monitoring, especially in reinforced concrete (RC) beam structures. While their application in this area has been well-documented, their use in RC columns remains relatively unexplored. This suggests a promising avenue for further research and development. This paper presents a thorough comparison of long-gauge fiber optic sensors and traditional measurement tools when used to monitor RC columns under small eccentric compressive loading. The evaluation focuses on the stability and precision of each sensor type. A monitoring system was developed for laboratory testing to assess the performance of various sensor types under specific conditions. The system incorporated four measurement schemes, utilizing a combination of embedded and surface-mounted long-gauge fiber optic sensors, linear variable differential transformers (LVDTs), and point sensors (strain gauges). Long-gauge fiber optic sensors, securely mounted on the concrete surface near the tensile side, were found to accurately measure both large and small deformations, outperforming LVDTs. Compared to strain gauges and embedded optic sensors, the long-gauge fiber optic sensors demonstrated superior average strain measurement and minimal interference from protective covers.