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Distributed strain measurements of prestressed concrete elements with fibre optic sensors The article presents the application of the technology of distributed strain measurements to prestressed concrete members. Distributed fibre optic sensing technology is based on light backscattering and enables strain measurements with high spatial resolution over the entire length of the optical fibre. Such an approach allows the replacement of thousands of conventional spot strain gauges, arranged in series, with a single optical fibre. The article presents composite fibre optic sensors and their application for strain measurements and crack development investigations. Three practical examples of prestressed concrete elements were described, namely truck scale platforms, prestressed concrete girders with a length of 24 meters, and one of the largest bridges in Poland. The structural members were analysed at different stages of construction, during fabrication and hardening, tendon activation, installation, proof loading, and also as a post‐installed measurement system. The aim of this article was to demonstrate the possibilities of measurements with composite distributed fibre optic sensors. [ABSTRACT FROM AUTHOR]

Validation of distributed fiber optic sensor technology for strain measurement in concrete structures Because of Structural Health Monitoring (SHM), the importance of fiber optic sensors in civil engineering has increased immensely [1]. An innovative method is the distributed fiber optic strain (DFOS) measurement using Rayleigh scattering [2], also termed distributed sensing. This technique provides a high spatial resolution and measurement sensitivity at each point of the measuring fiber so that the smallest strain changes can be recorded. However, there are no quality standards that guarantee reliable use in strain measurement. To establish such standards, the Structural Concrete Institute at the HTWK Leipzig validated the use of different fiber coating adhesive configurations for scenarios in concrete construction [3]. The results are promising: Compared to the reference measurement methods, the fiber optic sensor technology showed strain losses due to coating and/or adhesive of less than 5 %; and less than the data of the literature. [ABSTRACT FROM AUTHOR]

Test Set‐Ups on corrosion damaged cantilever walls – research project SIBS Retaining walls such as other structures are subjected to ageing or other environmental influences. Concrete structures, and especially RC‐structures, suffer from concrete spalling, cracking or corrosion. Given by slender cross sections and high degrees of reinforcement (e. g. cantilever walls) corrosion damages can influence the bearing capacity and the stability. Especially the earth‐sided regions of such structures (position of the bending reinforcement) and the connection areas between the vertical wall and the foundation slab can be subjected to such damage. In these areas, a non‐uniform and wide‐ranging corrosion pattern can be found, which is not visible during an inspection. This report gives a short overview on (corrosion related) damages and there causes, as well as a short insight in testing methods used for the safety assessment. Furthermore, a monitoring concept for corrosion damaged RC‐structures is presented. The installation and the validation of this concept is shown on a series of mock‐ups and the results are compared with numerical parameter studies. [ABSTRACT FROM AUTHOR]

Abstract: Distributed strain sensing in geotechnics – part 2 – tender texts for distributed fiber optic measurements in geotechnical engineering This contribution is a first contribution regarding distributed strain sensing in geotechnical engineering. In particular, the past shows a lot of uncertainty of the planning engineer with regard to request for proposals, especially dealing with the definition of “What” to request for. The field of the local distributed fiber optic sensor technology is, as already mentioned, a wide area. The following reports apply to both distributed temperature sensing and distributed strain sensing. The collected tender extent is based on an up to 25‐year‐old activity in the field of fiber‐optical measurement technology in the oil and gas industry, in hydraulic engineering and geotechnics. The following explanations in this contribution apply to distributed strain sensing. The system described is commercially distributed and is not subject to any tender relevant restrictions. This contribution includes a brief general description of the services to be tendered in connection with tender blocks describing the desired output clearly to ensure that the engineer receives comparable offers. Nevertheless, this contribution does not protect the contractor regarding his own evaluation of the offered services in relation to the suitability and performance of the tenderer. Finally, two non‐exhaustive economic considerations between the distributed sensing and conventional measuring methods are compared. [ABSTRACT FROM AUTHOR]

Distributed fiber-optic strain measurement - application in reinforced concrete members Distributed fiber optic measurement based on Rayleigh scattering is a technique with new possibilities in the field of analysis and interpretation of experiments. However, the application is challenging and requires a lot of experience and practice. The measurement technique will be briefly described and subsequently the authors will show and explain the potential as well as challenges and limits of application based on two small experiments. [ABSTRACT FROM AUTHOR]

Glas wird oft lastabtragend eingesetzt, wobei aus Gründen der Sicherheit und des Tragverhaltens Laminate zum Einsatz kommen. Insbesondere kalt gebogene, durch Lamination formstabilisierte Gläser sind ein zunehmend nachgefragtes Produkt. Herstellungsprozess und Nutzung führen in solchen Laminaten zu teils unbekannten Spannungen, welche die Aufnahme äußerer Einwirkungen begrenzen. Optische Messverfahren mit polarisiertem Licht erlauben keine Erfassung dieser Spannungen. Dünne, innen auf die Gläser geklebte faseroptische Sensoren stellen eine mögliche Lösung dar: In Versuchen an kalt gebogenen Gläsern wird gezeigt, dass optische Sensorik dem Laminationsprozess standhält und sich für kontinuierliche Dehnungsmessungen in Glaslaminaten eignet. Fibre Optical Sensors for Strain Measurement in Cold Bent Glass Laminates. Many glass products, e.g. for structural application, are conceived as laminates for safety and load bearing behaviour reasons. Cold bent glass with shape preservation by lamination is another, increasingly popular technique. Due to manufacturing and application, such laminates can be subjected to unknown, varying interior stresses limiting the additional load bearing capacity. Optical measurement based on polarised light does not permit to determine these stresses. Thin, barely visible fibre optical sensors, glued to the interior glass surfaces, are a possible solution. R [ABSTRACT FROM AUTHOR]

Zur Beurteilung der Alkaliempfindlichkeit der Gesteinskörnung finden normativ der Betonversuch mit Nebelkammerlagerung bei 40 °C und alternativ der 60 °C-Betonversuch Anwendung. Als Beurteilungskriterium für den Schädigungsprozess wird bei beiden Verfahren die an Betonprismen diskontinuierlich ermittelte Dehnung herangezogen. Auch bei den zusätzlich in der Nebelkammer gelagerten Würfeln beschränkt sich die Schadensanalyse auf eine diskontinuierliche Verfolgung der maximalen Breite der Oberflächenrisse. Im Rahmen des Beitrags wird eine neuartige, bereits erfolgreich erprobte zerstörungsfreie Prüfmethodik vorgestellt. Diese ermöglicht durch eine gleichzeitige kontinuierliche Dehnungs-, Schallemissions- und Ultraschallmessung eine kontinuierliche Verfolgung der inneren Gefügeveränderungen in den Betonprüfkörpern während der AKR-provozierenden Lagerung. Dabei wurden drei zeitlich aufeinanderfolgende Phasen der inneren Gefügeveränderung mit einer Dominanz von Hydratation, Rissbildung sowie vermutlicher Rissverfüllung mit Reaktionsprodukten identifiziert. Die ablaufenden Rissbildungsprozesse wurden zusätzlich mit diskontinuierlich durchgeführten röntgentomografischen Untersuchungen zeitlich und räumlich visualisiert. Die CT-Befunde wurden durch mikroskopische Untersuchungen bestätigt. Analysis of ASR-induced damage processes in concrete Application of innovative measurement techniques The alkali-reactive potential of aggregates is assessed according to the German guidelines by two different test methods. These are the 40 °C fog chamber storage and as an alternative method the 60 °C concrete prism test. In both tests, the discontinuously measured expansion of ASR-generating stored concrete prisms is used as criterion for the internal damage process. The damage analysis of the cubes additionally stored in the 40 °C fog chamber is also restricted to the discontinuous measurement of the crack width on the cubes surfaces. This paper describes an innovative, already successfully applied, non-destructive measurement methodology. This methodology enables a continuous monitoring of the internal damage processes in ASR-generating stored concrete specimens due to a continuous recording of expansion, acoustic emission and ultrasonic velocity. Thereby, three sequent phases of internal structural changes dominated by hydration, crack formation and filling of the cracks with ASR-gel and/or other reaction products can be detected. The crack formation was temporally and spatially visualised by discontinuously applied X-ray computed tomography measurements. Microscopic analyses confirm the findings of the X-ray 3D-CT. [ABSTRACT FROM AUTHOR]