With the development of fiber optical technologies, fiber Bragg grating (FBG) sensors are frequently utilized in structural health monitoring due to their considerable advantages, including fast response, electrical passivity, corrosion resistance, multi-point sensing capability and low-cost production, as well as high accuracy and resolution over a long period. These characteristics allow FBG to be a proper alternative sensing element for displacement measurements. In this article, the recent sensing advances and principles of detection of FBG-based displacement sensors are illustrated. Specifically, the latest FBG-based displacement technologies are examined from three principles of detection, i.e., wavelength, intensity and phase signal demodulation. Regarding wavelength detection methods, the problem related to the cross-sensitivity can significantly be reduced depending on the new type of cantilever–FBG-based sensing developed. Vice versa, only the packaging method of FBG prestressed between two fixed ends can still avoid the chirp phenomenon in the reflection spectrum. Moreover, to attenuate the influence of temperature variations on the accuracy of FBG displacement sensors, specific temperature self-compensation structures were successfully designed according to the concepts of phase signal demodulation. In future investigations, different elastic structures and gratings manufactured through special fibers and new methodologies for temperature compensation will still highly refine the efficiency of FBG-based displacement sensors.

Prestressing methods were used to realize long-span bridges in the last few decades. For their predictive maintenance, devices and dynamic nondestructive procedures for identifying prestress losses were mainly developed since serviceability and safety of Prestressed Concrete (PC) girders depend on the effective state of prestressing. In fact, substantial long term prestress losses can induce excessive deflections and cracking in large span PC bridge girders. However, old unsolved problematics as well as new challenges exist since a variation in prestress force does not significantly affect the vibration responses of such PC girders. As a result, this makes uncertain the use of natural frequencies as appropriate parameters for prestress loss determinations. Thus, amongst emerging techniques, static identification based on vertical deflections has preliminary proved to be a reliable method with the goal to become a dominant approach in the near future. In fact, measured vertical deflections take accurately and instantaneously into account the changes of structural geometry of PC girders due to prestressing losses on the equilibrium conditions, in turn caused by the combined effects of tendon relaxation, concrete creep and shrinkage, and parameters of real environment as, e.g., temperature and relative humidity. Given the current state of quantitative and principled methodologies, this paper represents a state-of-the-art review of some important research works on determining prestress losses conducted worldwide. The attention is principally focused on a static nondestructive method, and a comparison with dynamic ones is elaborated. Comments and recommendations are made at proper places, while concluding remarks including future studies and field developments are mentioned at the end of the paper.

Testing methods are required for estimating prestress losses in Prestressed Concrete (PC) girder-bridges. They mainly include destructive approaches which cause significant damages. Conversely, dynamic nondestructive methods are unsuitable. Given these findings, a novel method for identifying residual prestress force in simply supported PC girder-bridges was implemented. Following the vertical load application in a three-point bending, the method estimates the prestress force by measuring the vertical deflection at a quarter or, alternatively, at the midspan of the PC girder-bridge. The method also requires information regarding its flexural rigidity. Particularly, the initial tangent Young’s modulus must be evaluated by compression tests on cores drilled at its quarter and midspan cross-sections after three-point bending. In absence of the geometric and/or material properties, the flexural rigidity can be estimated according to free vibrations. Secondly, the method comprises a reference solution, or a finite element model of the PC girder-bridge, in which the prestress force is unknown. Thirdly, the measured deflection becomes a parameter of the prestress force identification process. Accurate identifications are obtained when the deflection, under a higher vertical load, was precisely measured and the flexural rigidity was determined using reference solution and initial tangent Young’s modulus. In this article, the novel method was simulated on a simply supported PC beam-bridge subjected to time-dependent prestress losses for ≈9.5 months in the laboratory.

In this work, two new face structures of the open-air protection fence were investigated, where a method was proposed for analyzing the condensation of water vapor in the protection fence to search for a condensation zone. Another method for calculating the amount of condensed vapor in a multiwall protection fence with closed gap spacings was proposed. The analytical results illustrated that the magnitude of the range of temperature variations of the worked-out structures with gap spacings and without heat-reflecting screens was 7.14% lower, while the existence of heat-reflective screens reduced this value to 27.14%. The investigation of the water vapor transmission magnitude demonstrated that the steam permeability strength of the interior side and retaining walls of the developed buildings amounts to the standard one, while the usage of a locked air space with a thermo-reflective panel allows the movement of the appropriate condensing region over the external face of the fencing. Mass analysis of the precipitated vapor during the heating time of 1 m² of the retaining wall showed that in face structures in closed gap spacings with heat-reflective screens, the mass of the precipitated vapor was 24.8% greater relative to that of the face without heat-reflective screens. Moreover, the examination of the absence of distillation in the oxygenated gap spacing proved that, in the gap spacing in the considered face structures, the condensate does not fall out such that there is no aggregation of humidity according to the annual balance. Furthermore, the drying time of the face structure with heat-reflecting screens was 17.9% longer than that of the traditional one. The research results can complement the works performed earlier by the authors, as well as be applied in the engineering and construction of buildings to save thermal power, considering the climatic features of the development region.

Using the software ANSYS-19.2/Explicit Dynamics, this study performed finite-element modeling of the large-diameter steel pipeline cross-section for the Beineu-Bozoy-Shymkent gas pipeline with a non-through straight crack, strengthened by steel wire wrapping. The effects of the thread tensile force of the steel winding in the form of single rings at the crack edges and the wires with different winding diameters and pitches were also studied. The results showed that the strengthening was preferably executed at a minimum value of the thread tensile force, which was 6.4% more effective than that at its maximum value. The analysis of the influence of the winding diameters showed that the equivalent stresses increased by 32% from the beginning of the crack growth until the wire broke. The increment in winding diameter decelerated the disclosure of the edge crack and reduced its length by 8.2%. The analysis of the influence of the winding pitch showed that decreasing the distance between the winding turns also led to a 33.6% reduction in the length of the straight crack and a 7.9% reduction in the maximum stresses on the strengthened pipeline cross-section. The analysis of the temperature effect on the pipeline material, within a range from −40°C to +50°C, resulted in a crack length change of up to 5.8%. As the temperature dropped, the crack length decreased. Within such a temperature range, the maximum stresses were observed along the central area of the crack, which were equal to 413 MPa at +50°C and 440 MPa at −40°C. The results also showed that the presence of the steel winding in the pipeline significantly reduced the length of crack propagation up to 8.4 times, depending on the temperature effect and design parameters of prestressing. This work integrated the existing methods for crack localization along steel gas pipelines.