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Characterization of bond performance of textiles in cement matrices using fiber optic sensors
(2002)
Fibre optic sensors for monitoring in safety-relevant structures have to be validated in order to proof their reliability under typical structural load conditions. The reliable use of optical fibre sensors depends strongly on an appropriate and qualitative application. Diagnostics of the physical condition of embedded and surface-applied fibre optic strain sensors are demonstrated on field examples. Distributed strain measurement based on Rayleigh backscattering is used to determine breakage of the fibre, interface adhesion problems and to identify application related strain transfer mechanisms.
Reinforced concrete piles are used in case of structures that are constructed on soft ground to transfer the loads into deeper strata with sufficient bearing capacity. In order to determine the pile’s behavior and possible damage, static and dynamic pile tests are carried out. Dynamic measurements taken from the pile head can show the bearing behavior and structural integrity by using the theory of wave propagation. In order to receive more precise information about the pile features, now, a string of sensors is embedded at different levels of the pile. A fiber optic strain wave sensor, based on the extrinsic Fabry-Perot interferometer (EFPI), has already been developed and tested in full-scale field tests by Schallert (2010). It was possible to detect the introduced deformation caused by the static load and the dilatational wave during dynamic loading. Although the full-scale tests were successful, the engineering design of the sensor body left room - from the economical point of view - to be optimized. After laboratory tests with the optimized sensor, a cast-in-situ bored pile has been built at the BAM Test Site Technical Safety in Horstwalde, South of Berlin. Additionally to the EFPI sensors, fiber Bragg grating (FBG) sensors, temperature sensors and resistance strain gauge (RSG) sensors are embedded in order to compare the signals with each other. In this paper, the modified sensor and the Setup of the cast-in-situ bored pile along with results of dynamic tests are shown.
Zur Gründung von Bauwerken auf weichen, gering tragfähigen Böden werden unter anderem Betonpfähle, einzeln oder in Pfahlgruppen, eingesetzt. Deren Bewertung bzgl. Tragverhalten bzw. Integrität ist bei bestimmten Baugrundverhältnissen und Pfahlgeometrien schwierig. Hierfür werden statische und dynamische Pfahlprüfungen durchgeführt. Aus Messwerten vom Pfahlkopf bzw. vom oberen Pfahlbereich werden üblicherweise die notwendigen Aussagen abgeleitet. Eine genauere Bewertung ist möglich, wenn präzise Messwerte über die gesamte Pfahllänge vorliegen. Deshalb wurden hochauflösende betoneinbettbare Messwertaufnehmer auf Basis von Faser-Fabry-Perot-Sensoren entwickelt, die in Modell- und in realen Rammpfählen getestet wurden. Der Beitrag beschreibt den Sensor, die Installation und exemplarisch einige Testergebnisse zur Erfassung der Wellenausbreitung im Modellpfahl. Feldtests wurden zurzeit der Erstellung des Manuskripts erfolgreich begonnen.
Reinforced concrete piles are often used for structures on non-sufficiently bearing soil areas. Assessment of bearing capacity and bearing behaviour of large concrete piles remains a difficult task under specific soil conditions and pile geometries. Usually static and dynamic pile tests are carried out for quality assurance. From dynamic measurements taken only from the pile head, the bearing behaviour and structural integrity can be derived using the one-dimensional theory of wave propagation. More precise information about the pile features can be achieved by highly resolving fibre-optic sensors based on Fabry-Perot technology, distributed over several locations along the pile length. Small scale piles and real driven piles have been tested. This paper describes the sensor, the sensor installation, and experimental results of tests in laboratory as well as test results for recording the wave propagation in the small scale piles.
Ausgewählte Anwendungsbeispiele faseroptischer Sensoren im Ingenieurbau und in der Geotechnik
(2007)