A feature extraction methodology based on lamb waves is developed for the non-invasive detection and prediction of the gap in concrete–metal composite structures, such as concrete-filled steel tubes. A popular feature extraction method, partial least squares regression, is utilised to predict the gaps. The data is collected using the piezoelectric transducers attached to the external surface of the metal of the composite structure. A piezoelectric actuator generates a sine burst signal, which propagates along the metal and is received by a piezoelectric sensor. The partial least squares regression is performed on the raw sensor signal to extract features and to determine the relationship between the signal and the gap size, which is then used to predict the gaps. The applicability of the developed system is tested on two concrete-metal composite specimens. The first specimen consisted of an aluminium plate and the second specimen consisted of a steel plate. This technique is able to detect and predict gaps as low as 0.1 mm. The results demonstrate the applicability of this technique for the gap and debonding detection in concrete-filled steel tubes, which are critical in determining the degree of composite action between concrete and metal.
This study proposes a wireless laser displacement sensor system for in situ deflection monitoring of wind turbine blades. This system consists of a tower-installed laser displacement sensor system composed of a laser displacement sensor head, controller, Zigbee transmitter, and analog-to-digital converter module, combined with a mobile host that includes a Zigbee receiver and a laptop. In contrast to the approach of blade sensor installation, the laser displacement sensor system is installed in the tower to enable noncontact blade displacement monitoring. The concepts of direct noncontact remote sensing and actuation from the tower and remote power delivery from the tower to blade-installed sensors and actuators will enable various approaches for wind turbine structural health monitoring. The proposed system can easily identify problems related to deflection. The size of wind blades increases with energy demands. Due to the large size of wind turbines, current wind turbines are installed very high above ground level. It is impractical to monitor the results from laser displacement sensor through wired connection in these cases. Hence, wired connections of laser displacement sensors to base monitoring stations must be replaced with a wireless solution. This wireless solution is achieved using Zigbee technology. The output from the laser displacement sensor is fed to a microcontroller, which acts as an analog-to-digital converter. The output from the microcontroller is connected to the Zigbee transceiver module, which transmits the data, and at the other end, the Zigbee reads the data and displays it on a PC, from which users can monitor the condition of the wind blades.
Prolonged exposure to low pH conditions affects the durability of concrete. In this work, the effect of mullite, aluminum silicate, on the strength and the acid corrosion of mortar and concrete under induced accelerated conditions in sulfuric acid solutions at pH of 0.25 and 1 was studied. The characterization of physicochemical changes was performed using techniques including compressive strength, scanning electron microscopy, micro-X-ray fluorescence spectrometry, and the Vickers hardness test. The results indicate that the addition of mullite does not have any significant effect on the overall strength of mortar and concrete samples, while it significantly increases their resistance to corrosion caused by sulfate attack by 90%, therefore, it is expected to increase the life span and decrease the maintenance costs of concrete pipes subjected to acid corrosion in sewer environments. The inhibition efficiency is observed to be sensitive to acid concentration and was improved with increase in the amount of mullite in samples.
In this paper, a piezoelectric based sensory technique is proposed for detection of gap between surfaces of CFRP plate and concrete specimen and characterization of shrinkage of early-age concrete. The proposed technique uses propagation properties of the guided waves in the CFRP plate excited and received by piezoelectric based transducers attached to the external surface of the CFRP-strengthened concrete specimen. Measurement is conducted with fresh and hardened early-age concrete specimens and two CFRP plates at different gaps. A piezoelectric actuator is excited using sine burst signal and the generated wave is received by a sensor after propagation along the specimen. The received signal at different gap values is used to detect a gap. To quantify gap, damage indexes including correlation coefficient, peak-to-peak amplitude of resultant signal and root mean square deviation are used. The shrinkage of concrete is detected and predicted by comparing the damage indices at different gaps with the indices at different stages of early-age concrete. The proposed technique is 2 relatively simple with small transducers, one-sided, non-destructive, and cost-effective solution for gap detection and concrete characterization.
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