A SLOT-CUTTING TECHNIQUE FOR REPAIR AND REHABILIATION OF CONCRETE DAMS AFFECTED BY ALKALI-SILICA REACTION

The combined impacts of earthquake damage and aging of concrete material on vulnerable aged dam systems have been typical causes of structural failure. The possible malfunction or loss of these vital systems and components can have serious socio-economic consequences and impacts on potable water resource availability, crop irrigation, and electric power generation. Worldwide extensive work has been done to evaluate the structural safety of aged concrete dam system components and to develop suitable remedial action and rehabilitation strategies. This paper reports a Chemo-Thermo-Mechanical Finite Element model developed by the authors which was used to demonstrate the use of the Finite Element Method (FEM) to model the behavior of a synthetic dam if the concrete is affected by Alkali-Silica Reaction (ASR), applying the slot cutting rehabilitation technique. ASR is a destructive chemical reaction between the cement paste and siliceous aggregate components in concrete materials that causes long-term expansion and degradation of concrete structures, including dams. Slot cutting is recognized as one of the promising techniques suitable to repair concrete dams suffering from ASR. The results show that the FE model could predict the stress and displacement field before and after the sawing of the slot in an assumed dam affected by ASR and demonstrate a promising capability for modeling the repair strategies in real dams suffering from ASR.

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In this paper, the performance of U-slot Rectangular Microstrip Patch Antennas (RMSA) is analyzed by using different flexible substrates. The RMSA is designed to operate for a resonant frequency of 2.45 GHz with flexible substrate materials like Polydimethylsiloxane (PDMS), GML-1032 and Polyethylene. The antenna parameters like reflection coefficient, voltage standing wave ratio (VSWR), radiation pattern, bandwidth and cost are analyzed by keeping all the substrate height same and the value is 2.5mm. U-slot cutting is used in the patch to overcome the narrow bandwidth limitation in RMSA because U-slot tunes the higher order orthogonal mode resonance frequency of the patch with respect to fundamental mode to realize the wider bandwidth. The maximum bandwidth of 80MHz is achieved with the use of PDMS. The antenna is simulated using HFSS software.

Time-Efficient Trochoidal Tool Path Generation for Milling Arbitrary Curved Slots

Trochoidal (TR) tool paths have been a popular means in high-speed machining for slot cutting, owing to its unique way of cyclically advancing the tool to avoid the situation of a full tool engagement angle suffered by the conventional type of slot cutting. However, advantageous in lowering the tool engagement angle, they sacrifice in machining efficiency—to limit the tool engagement angle, the step distance has to be carefully controlled, thus resulting in a much longer total machining time. Toward the objective of improving the machining efficiency, in this paper, we propose a new type of TR tool path for milling an arbitrary curved slot. For our new type of TR tool path, within each TR cycle, rather than moving circularly, the tool moves in a particular way such that the material removal rate is maximized while the given maximum engagement angle is fully respected. While this type of TR tool path works perfectly only for circular slots (including straight ones), by means of an adaptive decomposition and then a novel iso-arc-length mapping scheme, it is successfully applied to any general arbitrarily curved slot. Our experiments have confirmed that, when compared with the conventional TR tool paths, the proposed new type of TR tool path is able to significantly reduce the total machining time by as much as 25%, without sacrificing the tool wear.