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Advanced Engineering Science

Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-13-11-2022-414

Abstract :

In the western regions of China with high seismic risks, many pre-stressed concrete continuous rigid-frame bridges with high piers and long spans have been constructed. Generally, cantilever construction technology is used, but the construction period is long. The bridge may suffer earthquakes during construction. The possible seismic damage to the main beam and pier of the rigid-frame bridges in the cantilever construction stage was explored under the strong earthquake. Based on the Miaoziping bridge, which had undergone the Wenchuan earthquake, three structural systems, i.e. maximum cantilever T-frame, asymmetric single cantilever T-frame of side-span-closure, and continuous rigid-frame of the completed bridge, were established to simulate the transition process of cantilever construction from statically indeterminate to once statically indeterminate to multiple statically indeterminate. The strong motion records near the bridge site during the Wenchuan earthquake were selected as the inputs for time history analysis. Combined with the actual earthquake damage of Miaoziping bridge in the completion state, the main beam stress, and piers internal force of the three system structures were analyzed under the strong earthquake. Compared with the bridge completion stage, the top plate and web at the consolidation of piers and girder were also prone to cracking in the maximum cantilever stage under strong earthquakes, but it was not easy to crack in most other positions; In the side-closure-stage, the (principal) tension stress and (principal) compressive stress were also relatively larger in the top plates and bottom plates near the closing section of side-span, the web near the 1/5 to 2/5 area of the side span, and the top plates and bottom plates near consolidation pier-beam, which were also prone to cracking, but the mid-span was not easy cracking. In the two construction phases, although the longitudinal bending moment at the middle-high position of piers was more than twice that of the completed bridge stage, it was not easy to crack; the top and bottom of the main pier were easy to crack, which was consistent with the response of the completed bridge. It is recommended that the seismic importance coefficients of class A continuous rigid frame bridges be 0.76 during the construction period. The research results provide a reference for the construction of high pier and long-span rigid frame bridges with cantilever construction technology meeting earthquakes.

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-13-11-2022-413

Abstract :

To study the mechanical properties of ferronickel slag–clay–cement (FNSCC) modified soil, the undrained triaxial compression tests of FNSCC modified soil under different ferronickel slag mixing ratios, moisture content and curing times were carried out. The stress-strain curve and secant elastic modulus of FNSCC modified soil samples under different working conditions were obtained, and the influence mechanism and failure mode of mechanical properties were analyzed. Based on the experimental results, the modified Duncan–Chang constitutive model suitable for FNSCC modified soil was established. The results show that the stress-strain curve of FNSCC modified soil has obvious strain softening characteristics. The peak strength first increases and then decreases with the increase of water content. The swelling failure of the sample with a water content of approximately 15 % is particularly obvious. The peak strength of FNSCC modified soil increases with the decrease of the ferronickel slag incorporation ratio. With the increase of the ferronickel slag incorporation ratio, the failure mode of specimens changed from bulging failure to shear failure. With the increase of curing time, the failure mode changes from a plastic failure such as bulging deformation to a brittle failure such as local tension crack. The secant elastic modulus of FNSCC modified soil decreases with the increase of axial strain. When the axial strain is less than 2%, the addition ratio of ferronickel slag, water content, and curing time have a great influence on the secant elastic modulus. When the axial strain is greater than 2%, each factor has little effect on the secant elastic modulus. The modified Duncan–Chang model can better reflect the strain softening phenomenon of FNSCC modified soil. The model parameters m, n and l are approximately linear with confining pressure. The model parameter m is most affected by the ratio of FNSCC modified soil, followed by the curing time, and the moisture content is the smallest. The curve calculated by the modified Duncan–Chang model is in good agreement with the measured curve, which verifies the rationality of the fitting parameters

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-13-11-2022-412

Abstract :

The rapids abating hydraulic index generally refers to the combination of the maximum route flow velocity and gradient of a ship which can sail through the rapids by itself under the condition of rated load and rated main engine power. It is the critical flow condition to determine whether the ship can sail through the rapids by itself, and it is the reference basis for analyzing the effect of rapids regulation. This paper analyzes the defects of the existing methods to determine the rapids abating hydraulic index, and points out the shortcomings of the existing expressions of comprehensive rapids abating hydraulic index, such as unreasonable selection of key parameters, unclear relationship between influencing factors and main variables, etc. Based on the basic relationship between flow resistance and flow velocity, gradient resistance and gradient, and according to the basic principle of the balance between ship thrust and navigation resistance, from the perspective of overcoming the existing shortcomings of the calculation and expression of the rapids abating hydraulic index, a traditional expression and pre-estimation formula of dimensionless rapids abating hydraulic index were derived. Applying the test results of 500-ton ship at hydrostatic speed in Lancang River, the variation law between the ratio of actual propeller speed to the rated propeller speed with the advancing coefficient was obtained. When calculating the rapids abating hydraulic index, the propeller speed should not be taken as the rated speed. The results show that there is an obvious deviation between the flow resistance calculated by the Zvankov formula and the ship thrust. The correction curve of the resistance correction coefficient with the ship Froude number was plotted. It is pointed out that the calculation formula of Zvankov flow resistance needs to be properly modified according to the results of full-scale ship test. The rapids abating hydraulic indexes of various types of motor ships in Lancang River were analyzed and calculated, and the rationality of the traditional expression of dimensionless rapids abating hydraulic index were verified. It is proved that the dimensionless parabola is more appropriate to describe the relationship between flow velocity and gradient in the rapids abating hydraulic index. Based on the principle of dimensional analysis and through the numerical regression analysis of the rapids abating hydraulic indexes of various motor ships in Lancang River, the pre-estimation formula of dimensionless rapids abating hydraulic index was established, which can significantly improve the calculation efficiency of the rapids abating hydraulic index.

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-13-11-2022-411

Abstract :

In conventional dam displacement monitoring models, forecast precision is below the standard, the fitting residual sequence contains chaotic components, and information mining of dam prototype observation data is limited. In consideration of the chaotic characteristics of the fitting residual sequence in regression model, the multi-scale wavelet analysis is used to decompose and reconstruct the residual sequence in this study; back propagation neural network and autoregressive integrated moving average model are used to forecast the reconstructed residual sequence by identifying the high-frequency and low-frequency characteristics of signals. By superimposing the residual forecast value with the forecast value of regression model, the combination forecast model for concrete dam displacement considering residual correction is proposed. Examples show that, compared with conventional models, the proposed combination model is better in fitting precision and convergence speed. Forecast capability is significantly improved for dam displacement forecast when effective components contained in residual sequence are considered. A new method of displacement forecast for high slope and other hydraulic structures is presented.

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-13-11-2022-410

Abstract :

Saccharin (SAC) is an emerging contaminant, widely detected in the environment, with potential ecotoxicity risks to aqueous organisms and human beings. Wastewater treatment plants (WWTPs) are key sources and sinks of SAC, and play a vital role in eliminating SAC entering the environment. An overview is provided of the potential ecotoxicity of SAC, its occurrence in the aqueous environment, and its degradation performance in WWTPs. SAC treatments, including physical, chemical (mainly advanced oxidation processes AOPs), biological, and hybrid processes, and possible degradation mechanisms are also considered. Of the various SAC removal processes, we find that adsorption-based physical methods exhibit relatively poor performance in terms of SAC removal, whereas chemical methods, especially hydroxy radical-mediated oxidation processes, possess excellent capacities for SAC elimination. Although biological degradation can be efficient at removing SAC, its efficiency depends on oxygen supply and the presence of other co-existing pollutants. Hybrid aerobic biodegradation processes combined with other treatments including AOPs could achieve complete SAC reduction. Furthermore, novel adsorbents, sustainable chemical methods, and bioaugmentation technologies, informed by in-depth studies of degradation mechanisms and the metabolic toxicity of intermediates, are expected further to enhance SAC removal efficiency and enable comprehensive control of SAC potential risks

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