This article presents laboratory tests, with the purpose being to verify the suitability of standard optical fibres in a tight jacket for advanced strain analysis within concrete members. An optical reflectometer was used to enable the optical signal to be processed on the basis of the Rayleigh scattering phenomenon, so that strains and/or temperature changes were determined along the length of the measuring fibre. The measurements were carried out continuously in a geometrical sense (distributed measurements), with a spatial resolution starting from as fine as 5 mm. The arrangement of optical fibres inside the heterogeneous concrete medium and on its surface allowed for the identification and detailed analysis of local phenomena such as cracks. Remote and early location of structural damage with an estimation of its scale provides new opportunities for the monitoring of the structural health of reinforced concrete structures, facilitating the interpretation of its behaviour as well as failure risk management based on comprehensive and reliable measurement data. If traditional spot techniques are used, this approach is not possible. The aim of the initial studies was to analyse the strain distributions over compressed and tensioned measurement sections located on the surface of a cylindrical specimen of concrete. In the tests which followed, the reinforced concrete rod was eccentrically tensioned with fibre optics installed inside. Qualitative and quantitative verification of crack widths was made, with a narrow range up to 0.05 mm and a wider one to 0.30 mm. The results of the studies show very good accuracy of optical fibre sensor technology as a reference technique during the analysis of microcracks and narrow cracks, and moderate accuracy in the case of wider cracks. Despite using optical fibres in a tight jacket which mediates in strain transfer, the results obtained can be very suitable for the assessment of the structural condition of the member under consideration. It is also worth noting that the tests conducted indicate the effectiveness of distributed optical fibre technology for the analysis of concrete homogeneity and its structural behaviour within compressed areas, as it is possible to calculate strains over measuring bases that start from lengths as short as 5 mm.

This paper presents graphs and formulas serving to define the distribution of the restraint degree of wall segments in rectangular reinforced concrete tanks. The most frequent cases occurring in engineering practice are analyzed, that is, wall segments erected during the first concreting stage and those restrained along three edges. For the latter ones, this paper defines the influence of vertical stiffness in construction joints (depending on the reinforcement degree) on the distribution of the restraint degree. This paper shows a substantial impact of the temperature profile (i.e., imposed strain resulting from the development of hydration heat) on the area where cracks occur first, and on the value and distribution of tensile stresses. A practical aspect of the analysis performed is the possibility of defining the restraint degree for cases and assumptions not included in EN 1992–3.

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Crack control throughout the service life of a structure has always been a challenging task for engineers and asset owners, particularly those who are involved with the design and construction of structures with increased durability requirements, such as liquid retaining structures, nuclear containment buildings or structures in direct contact with ground, but also other externally restrained structures. For these reasons, several standardized methods exist throughout the global engineering community which encompass differences between them. This work is a state‐of‐the‐art review of the methods for crack width control due to imposed strains recommended by different regulatory documents from Europe, USA, Australia and Japan, and provide a reasonable degree of guidance with respect to the assumptions, possibilities and restrictions of each method. This work resonates with the scope of the RILEM TC 287‐CCS: Early age and long‐term crack width analysis in RC structures.