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Assessing the Instantaneous Stiffness of Cracked Reinforced Concrete Beams Based on a Gradual Change in Strain Distributions
Concrete cracking causes a gradual change in strain distributions along the cross section height of reinforced concrete beams, which will finally affect their instantaneous stiffness. A method for assessing the stiffness is proposed based on the gradual change, which is considered through modeling different strain distributions for key sections in cracked regions. Internal force equilibria are adopted to find a solution to top strains and neutral axes in the models, and then the inertias of the key sections are calculated to assess the beam stiffness. The proposed method has been validated using experimental results obtained from tests on five reinforced concrete beams. The predicted stiffness and displacements are shown to provide a good agreement with experimental data. The instantaneous stiffness is proven to greatly depend on the crack number and depth. This dependence can be exactly reflected by the proposed method through simulating the gradual change in concrete strain distributions.
Mechanism of Degradation of the Properties of Recycled Plaster Mixed Aluminate Cement
This manuscript investigates the degradation of the properties of recycled plaster-mixed aluminate cement (RAP) and analyzes its degradation mechanism by DSC/TG and SEM. The results showed that the setting time of RAP was shortened due to the fast formation of recycled ettringite (AFt) and its strength was decreased relative to the pure recycled plaster (RP) in the absence of aluminate cement. Different from the properties of RP and RAP, the hydration of commercial plaster was slowed down by the addition of aluminate cement for its low hydration rate, and its strength was increased with respect to the pure commercial plaster (CP) without aluminate cement. Therefore, the properties of RP and RAP could be seen to decrease in relation to CP and commercial plaster mixed aluminate cement (CAP). The SEM and DSC/TG analyses confirm the presence of cluster and fine crystals and noncementing AH3 in RAP, which demonstrates its degradation of properties.
Magnetorheological Elastomer Precision Platform Control Using OFFO-PID Algorithm
The magnetorheological elastomer (MRE) is a kind of smart material, which is often processed as vibration isolation and mitigation devices to realize the vibration control of the controlled system. The key to the effective isolation of vibration and shock absorption is how to accurately and in real time determine the magnitude of the applied magnetic field according to the motion state of the controlled system. In this paper, an optimal fuzzy fractional-order PID (OFFO-PID) algorithm is proposed to realize the vibration isolation and mitigation control of the precision platform with MRE devices. In the algorithm, the particle swarm optimization algorithm is used to optimize initial values of the fractional-order PID controller, and the fuzzy algorithm is used to update parameters of the fractional-order PID controller in real time, and the fractional-order PID controller is used to produce the control currents of the MRE devices. Numerical analysis for a platform with the MRE device is carried out to validate the effectiveness of the algorithm. Results show that the OFFO-PID algorithm can effectively reduce the dynamic responses of the precision platform system. Also, compared with the fuzzy fractional-order PID algorithm and the traditional PID algorithm, the OFFO-PID algorithm is better.
Effect of Nanoclays on Moisture Susceptibility of SBS-Modified Asphalt Binder
Moisture susceptibility plays an important role in the damage of asphalt pavement. Failure occurs when asphalt is removed from the aggregate particles due to the decreased adhesion between the asphalt and aggregate in comparison with that between water and the aggregate. In recent years, efforts utilizing nanomaterials to improve the diverse properties of asphalt have proven to be effective. In this study, three types of nanoclays were used to modify styrene-butadiene-styrene- (SBS-) modified asphalt. The resistances to water damage of the modified binders were evaluated using the surface free energy (SFE) and atomic force microscopy (AFM). The results revealed that the total SFE decreased and the energy ratio (ER) increased when the asphalt binder was modified with the nanoclays, indicating that the addition of nanoclays can improve the moisture resistance of these aggregate-binder systems. After immersion, a decreased amount of bee structures was observed in both the SBS and nanoclay-modified asphalts due to the interactions between water and bitumen. However, the residual amount of bee structures was higher in the nanoclay-modified asphalts than in the SBS-modified asphalt, indicating that the addition of nanoclay makes the surface morphology of asphalt more resistant to water damage. Finally, freeze-thaw splitting tests were used to verify the results obtained through the SFE and AFM tests.
Cherenkov Emission Generated by a Modulated Source in 2D Dispersive Photonic Crystal Slabs
This work presents a systematic numerical study of Cherenkov optical radiation generated by a modulated source that moves with uniform velocity on a two-dimensional (2D) photonic crystal (PCr) slab surface. We apply the FDTD technique with emphasis on the dispersion properties of the periodic medium to perform our numerical analysis. The field oscillations generated at the passage of a modulated source in the PCr produce a series of spectral resonances corresponding to the eigenmodes in the spatial frequency domain for the photonic slab. The amplitudes of the field oscillations have maximal values in the group cone closely to the path of the moving charge.
Analysis of Bond Behavior of FRP-Confined Concrete Piles Based on Push-Out Test
Due to the significant differences in the properties (e.g., anisotropy, elasticity modulus, and surface roughness) of fibre-reinforced polymer (FRP) and traditional pile materials, research on bond behavior between FRP tube and concrete should be conducted to ensure that they can work together properly. Push-out tests on twenty-nine GFRP-confined concrete piles were performed, the influence of bond type, slenderness ratio of FRP tube, radius-thickness ratio of FRP tube, concrete stress and concrete type on bond behavior and distribution of axial strains were studied, and simplified bond-slip constitutive models based on test results were proposed. It was found that bond type was a critical factor influencing bond behavior. A smaller radius-thickness ratio, a higher concrete stress, and the use of expansive concrete were advantageous for achieving higher bond behavior, whereas the slenderness ratio had little influence on the bond behavior. The axial strain distribution of all FRP tubes demonstrated the following rules: the upper strain was greater than the middle strain, which was larger than the lower strain, but for normal concrete specimens, the strain was linearly distributed with height, while for expanded concrete specimens, the distribution curves were polylines.