1Einführung und Motivation Nach [3] The results gained in this manner will never depict the reality because of the not considered heavily non-linear behavior of concrete. A way to improve the results is the application of monitoring sensors, which are able to image the changes in the inner part of the concrete matrix independently from applied loads. In this article a monitoring concept will be proposed which can achieve these objectives. The laboratory tests are already described in [2] and now a deeper assessment of the measured results will be made. At the end of this article dynamic tests with prestressed railway sleepers and mounted monitoring system are presented. The measurement data of the sensors will be correlated with results of a numerical nonlinear simulation of the sleeper.
Glasfaser-oder textilbewehrte Betonplatten sind für dünnwandi-ge Flächentragwerke wegen ihren guten mechanischen Eigenschaften und ihrer ausgeprägten Duktilität besonders geeignet. Diese Platten werden zumeist als Fertigteile hergestellt und kön-nen für den Bau von Schalen und Platten optimal eingesetzt werden. Für die Herstellung von großflächigen Flächentragwerken ist jedoch eine praktikable Fügetechnik notwendig. Das Fügen der Platten wird hier durch Vorspannung bewerkstelligt, wodurch es möglich ist, lediglich stumpf gestoßene Platten so miteinander zu verbinden, dass sie neben Normalkräften auch Momente in der Fuge übertragen können. In experimentellen Untersuchungen wurden die verwendeten Platten und die Fügetechnik getestet. Abschließend wurde noch ein Bogen mit hoher Schlankheit prä-sentiert, der mit dieser Fügetechnik gebaut wurde. Joining of Fiber Reinforced Concrete Plates and Shells by Post-TensioningGlass fibre and textile reinforced concrete slabs are suitable for thin walled surface structures due to their good mechanical properties and their pronounced ductility. These plates are usually produced as precast elements and can be used for shell and slab structures. For the creation of large surface structures a viable connection technique is necessary. The connection of the plates will be established by post-tensioning: This allows for a blunt connection, which is able to transfer normal forces and moments across the connection. The plates and the connection technology were tested in experimental investigations. Finally, a feasibility study was made by erecting a very slender arch with this connection technology. Einleitung
This study investigates the detection of delaminations in concrete plates using non-contact laser ablation instead of the conventional hammer excitation. Tests were performed on two specimens of which one had an artificial delamination. 5 mm to 15 mm diameter steel tip hammers were used as a reference source and compared to a 7 ns pulsed 1064 nm Nd:YAG laser with 150 mJ pulse energy. Signals were recorded by surface- mounted accelerometers and in air by microphones and a laser Doppler vibrometer. Frequencies up to 150 kHz are excited with a broad frequency spectrum and little energy compared to the narrower frequency spectra of the hammers. The characteristic thickness resonance frequency of the intact plates can be accurately detected by the hammer excitation. The laser can excite low frequency flexural vibration modes over a shallow delamination at 3 cm depth, but does not excite the thickness resonance frequency. The low frequency flexural vibrations are verified by numerical natural frequency analysis.
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