作者机构：
[Cao Guo-hui; Zhang Kai] Hunan City Univ, Coll Civil Engn, Yiyang 413000, Peoples R China.;[Hu Jia-xing] Hunan Univ, Coll Civil Engn, Changsha 410082, Peoples R China.
通讯机构：
[Cao Guo-hui] H;Hunan City Univ, Coll Civil Engn, Yiyang 413000, Peoples R China.
关键词：
prestress;relaxation loss;shrinkage and creep;theoretical analysis;calculation model
摘要：
The calculation model for the relaxation loss of concrete mentioned in the Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts (JTG D62—2004) was modified according to experimental data. Time-varying relaxation loss was considered in the new model. Moreover, prestressed reinforcement with varying lengths (caused by the shrinkage and creep of concrete) might influence the final values and the time-varying function of the forecast relaxation loss. Hence, the effects of concrete shrinkage and creep were considered when calculating prestress loss, which reflected the coupling relation between these effects and relaxation loss in concrete. Hence, the forecast relaxation loss of prestressed reinforcement under the effects of different initial stress levels at any time point can be calculated using the modified model. To simplify the calculation, the integral expression of the model can be changed into an algebraic equation. The accuracy of the result is related to the division of the periods within the ending time of deriving the final value of the relaxation loss of prestressed reinforcement. When the time division is reasonable, result accuracy is high. The modified model works excellently according to the comparison of the test results. The calculation result of the modified model mainly reflects the prestress loss values of prestressed reinforcement at each time point, which confirms that adopting the finding in practical applications is reasonable.
作者机构：
[Zhou, Z. -M.; Zhang, J. -F.; Long, Q.] Hunan City Univ, Sch Civil Engn, Yiyang 413000, Hunan, Peoples R China.
通讯机构：
[Zhang, J. -F.] H;Hunan City Univ, Sch Civil Engn, Yiyang 413000, Hunan, Peoples R China.
关键词：
Multi-objective model;Traffic management strategy;Intersection signal controlling;Fuzzy analytic process;Q-learning algorithm
摘要：
Traffic signals are one of the main traffic management tools used to control traffic flow on the roads and should reflect traffic managers' intentions in different tasks. This paper showed a multi-objective optimization model, and its algorithm was aimed at the intricate structure of traffic control. First, the indexes of queuing lengths, delay times, and stop times were chosen as the evaluation indexes of optimization model. Second, the weight of the optimization indexes was confirmed with a fuzzy analytic process (FAP) according to the traffic managers' strategy. Finally, the multi-objective optimization model was solved with the Q-learning algorithm, and thus the signal control scheme of the intersection was produced in real-time while considering the traffic management strategy. The results of the simulation showed that the method could effectively improve traffic efficiency at the intersection, and at the same time, the intentions of the traffic managers could be fully embodied.
作者机构：
[Yin Tu-bing; Liu Xi-ling; Li Xi-bing; Rao Meng] Cent S Univ, Sch Resources & Safety Engn, Changsha 410083, Peoples R China.;[Liu Xi-ling] Univ British Columbia, Norman B Keevil Inst Min Engn, Vancouver, BC V6T 1Z4, Canada.;[Hong Liang] Hunan City Univ, Sch Civil Engn, Yiyang 413049, Peoples R China.
通讯机构：
[Liu Xi-ling] C;Cent S Univ, Sch Resources & Safety Engn, Changsha 410083, Peoples R China.
摘要：
Acoustic emission tests were performed using a split Hopkinson pressure bar system (SHPB) on 50-mm-diameter bars of granite, limestone, sandstone and skarn. The results show that the amplitude distribution of hits is not well centralized around 50 dB, and that some hits with large amplitudes, usually larger than 70 dB, occur in the early stages of each test, which is different from the findings from static and low-loading-rate tests. Furthermore, the dominant frequency range of the recorded acoustic emission waveforms is between 300 kHz and 500 kHz, and frequency components higher than 500 kHz are not significant. The hit with the largest values of amplitude, counts, signal strength, and absolute energy in each test, displays a waveform with similar frequency characteristics and greater correlation with the waveform obtained from the elastic input bar of the split Hopkinson pressure bar system compared with the waveforms of the other hits. This indicates that the hit with the largest values of amplitude, counts, signal strength, and absolute energy is generated by elastic wave propagation instead of fracture within the rock specimen.
摘要：
Cast-in-place concrete large-diameter pipe pile (referred to as PCC pile) is widely used for pile-supported embankment over soft soils in China. However, the studies focused on the sliding stability and calculated method of this new pile type under lateral load was relatively little. Therefore, base on PCC pile-supported embankments in the eastern coastal region of China case study, undrained shear strength, conventional p-y criteria, and modified pile modulus are recommended for lateral bearing capacity calculation basing on LPILE plus 5.0. The correctness of calculated method is verified by comparing the results on lateral load versus pile top deflection with those obtained by field test. The performances of drilled shaft with the same out-diameter, and PCC pile without considering pile core soils are also carried out for comparative analysis. The result shows that the performances of PCC piles under lateral load can be calculated through LPILE software with conventional p-y criteria of drilled shaft, and modified modulus of piles. The result also shows that when comparing with conventional drilled shaft with the same out-diameter, the lateral bearing capacity of PCC pile is reduced nearly about 20 %, while with nearly about 60 % concrete usage are saved. The results of this paper can provide design and calculation guide for practical PCC pile used for landslide disaster treatment under lateral load in United States.
摘要：
The response surface method (RSM) is one of the main approaches for analyzing reliability problems with implicit performance functions. An improved adaptive RSM based on uniform design (UD) and double weighted regression (DWR) was presented. In the proposed method, the basic principle of the iteratively adaptive response surface method is applied. Uniform design is used to sample the fitting points. And a double weighted regression system considering the distances from the fitting points to the limit state surface and to the estimated design points is set to determine the coefficients of the response surface model. Compared with the conventional approaches, the fitting points selected by UD are more representative, and a better approximation in the key region is also observed with DWR. Numerical examples show that the proposed method has good convergent capability and computational accuracy.
作者：
Li Wen-bin;Pan Qing-lin*;Xiao Yan-ping;He Yun-bin;Liu Xiao-yan
期刊：
中南大学学报(英文版),2011年18(2):279-284 ISSN：2095-2899
通讯作者：
Pan Qing-lin
作者机构：
[Pan Qing-lin; Li Wen-bin; Xiao Yan-ping; Liu Xiao-yan; He Yun-bin] Cent S Univ, Sch Mat Sci & Engn, Changsha 410083, Peoples R China.;[Li Wen-bin] Hunan City Univ, Sch Civil Engn, Yiyang 413000, Peoples R China.
通讯机构：
[Pan Qing-lin] C;Cent S Univ, Sch Mat Sci & Engn, Changsha 410083, Peoples R China.
关键词：
Al-Zn-Cu-Mg-Sc-Zr alloy;retrogression and re-aging treatment;microstructure;mechanical properties;stress corrosion cracking
摘要：
The mechanical properties and stress corrosion cracking (SCC) resistance of an Al-Zn-Cu-Mg-Sc-Zr alloy under different aging conditions were investigated. The dependence of microstructure and mechanical properties on aging parameters was evaluated by tensile test, hardness test and conductivity measurement. The results show that for the alloys with retrogression and re-aging treatment (RRA), the conductivity increases with the retrogression time and temperature, while the tensile strength decreases. The transmission electron microscopy (TEM) results show that the precipitates η(MgZn2) at grain boundary aggregate apparently with retrogression time and the precipitates inside the matrix exhibit the similar distribution to T6 temper, which comprises fine GP zones, large η′(MgZn2) and η(MgZn2) phases. According to the mechanical properties and microstructure observations, the optimal RRA regime is recommended to be 120 °C, 24 h + 180 °C, 30 min + 120 °C, 24 h. The strength level of the alloy after the optimum RRA treatment is similar to that in T6 condition and the SCC resistance is improved obviously in contrast to T6 condition.
作者：
Jin, Z. R.;Zhang, D. M.;Wang, Y. H.*;Li, Z. L.
期刊：
Engineering Analysis with Boundary Elements,2011年35(11):1204-1213 ISSN：0955-7997
通讯作者：
Wang, Y. H.
作者机构：
[Jin, Z. R.] Hunan City Univ, Sch Civil Engn, Yiyang 413000, Hunan, Peoples R China.;[Zhang, D. M.; Wang, Y. H.; Li, Z. L.] Huazhong Univ Sci & Technol, Sch Civil Engn & Mech, Wuhan 430074, Hubei, Peoples R China.
通讯机构：
[Wang, Y. H.] H;Huazhong Univ Sci & Technol, Sch Civil Engn & Mech, Wuhan 430074, Hubei, Peoples R China.
关键词：
Boundary element method;Dynamic element discretization method;Isoparametric elements;Traction boundary integral equation
作者机构：
[Pan, Qing-Lin; Li, Wen-Bin; He, Yun-Bin; Xiao, Yan-Ping; Liu, Xiao-Yan] Cent S Univ, Sch Mat Sci & Engn, Changsha 410083, Peoples R China.;[Pan, Qing-Lin] Minist Educ, Key Lab Nonferrous Mat Sci & Engn, Changsha 410083, Peoples R China.;[Li, Wen-Bin] Hunan City Univ, Sch Civil Engn, Yiyang 413000, Peoples R China.
通讯机构：
[Xiao, Yan-Ping] C;Cent S Univ, Sch Mat Sci & Engn, Changsha 410083, Peoples R China.
关键词：
A. Non-ferrous metals and alloys;E. Corrosion;F. Microstructure
摘要：
Influence of retrogression and re-aging treatment on the microstructure, strength, exfoliation corrosion, inter-granular corrosion and stress corrosion cracking of an Al-Zn-Mg-Cu alloy has been investigated by means of optical microscope (OM), transmission electron microscope (TEM) and electrochemical impedance spectroscopy (EIS). The results show that retrogression and re-aging treatment can increase the size and the distribution discontinuity of the grain boundary precipitates, and lead to the increase of the corrosion resistance without the loss of strength and ductility. In addition, the analysis of electrochemical impedance spectroscopy shows that retrogression and re-aging treatment can enhance the resistance to exfoliation corrosion. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.
作者机构：
[Pan Qing-lin; Li Wen-bin; Xiao Yan-ping; Liu Xiao-yan; He Yun-bin] Cent S Univ, Sch Mat Sci & Engn, Changsha 410083, Hunan, Peoples R China.;[Li Wen-bin] Hunan City Univ, Sch Civil Engn, Yiyang 413000, Peoples R China.
通讯机构：
[Pan Qing-lin] C;Cent S Univ, Sch Mat Sci & Engn, Changsha 410083, Hunan, Peoples R China.
摘要：
The microstructural evolution and composition distribution of an Al-Zn-Cu-Mg-Sc-Zr alloy during homogenization were investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results show that severe dendritic segregation exists in Al-Zn-Cu-Mg-Sc-Zr alloy ingot. There are a lot of eutectic phases at grain boundary and the distribution of the main elements varies periodically along interdendritic region. The main eutectic phases at grain boundary are Al7Cu2Fe phase and T (Al2Mg3Zn3). The residual phases are dissolved into the matrix gradually during homogenization with increasing temperature and prolonging holding time, which can be described by a constitutive equation in exponential function. The overburnt temperature of the alloy is 473.9 °C. The optimum parameters of homogenization are 470 °C and 24 h, which is consistent with the result of homogenization kinetic analysis.
摘要：
In order to present basic guidance for system calibration of split Hopkinson pressure bar (SHPB) with the special shape striker, wave characteristics and dynamic responses of SHPB under striker impact were analyzed. Stress generated by the special shape striker tends to have a half-sine waveform and has little wave dispersion during its propagation. Impact velocities of the special shape striker and peak values of generated stress still have linear relation but with a different coefficient from that of cylindrical strikers. From stress histories on the surfaces of the input bar impacted by the special shape striker off-axially and obliquely, it is found that the misalignment impacts usually trigger wave distortion and amplitude decrease, which can be used to identify the poor system adjustment. Finally, the system calibration of SHPB with the special shape striker can be classified into four steps: system adjustment, wave distortion identification, measurement calibration and transmission calibration, where the measurement calibration factor and transmission calibration factor are elaborated and redefined.
摘要：
The mechanical performance of recycled aggregate concrete (RAC) is investigated. An experiment on the complete stress-strain curve under uniaxial compression loading of RAC is carried out. The experimental results indicate that the peak stress, peak strain, secant modulus of the peak point and original point increase with the strength grade of RAC enhanced. On the contrary, the residual stress of RAC decreases with the strength grade enhancing, and the failure of RAC is often broken at the interface between the recycled aggregate and the mortar matrix. Finally, the constitutive model of stress-strain model of RAC has been constituted, and the results from the constitutive model of stress-strain meet the experiment results very well.
作者机构：
[Jiang Jian-qing; Yang Guo-lin] Cent S Univ, Sch Civil & Architectural Engn, Changsha 410075, Hunan, Peoples R China.;[Jiang Jian-qing] Hunan City Univ, Sch Civil Engn, Yiyang 413000, Peoples R China.
通讯机构：
[Jiang Jian-qing] C;Cent S Univ, Sch Civil & Architectural Engn, Changsha 410075, Hunan, Peoples R China.
关键词：
red-sandstone;large-scale field test;mechanical characteristic;strength parameter
摘要：
Large-scale field shear tests on ten specimens of the red-sandstone embankment at a highway in Hunan, China, were performed to examine mechanical characteristics and parameters of red-sandstone. The curves of thrust-displacement, failure mode, and shear strength parameters for red-sandstone with different water contents, different compactions, and different grain size distributions were obtained from the tests. A practical procedure of in-situ test for red-sandstone embankment was proposed to normalize the test equipment and test steps. Based on three-dimensional thrust-sliding limit equilibrium method, the formulas for calculating strength parameters of red-sandstone considering three-dimensional sliding surface were inferred. The results show that red-sandstone has typical complete curves of stress-strain, strain softening, which are caused by the special structure of red-sandstone; water content and compaction are important factors for strength and failure mode of red-sandstone; The average value of cohesion and internal friction angle of the specimens calculated by three-dimensional technique are 21.56 kPa and 29.29°, respectively, and those by traditional two-dimensional method are 25.52 kPa and 33.76°, respectively.
摘要：
In order to determine the relationship among energy consumption of rock and its fragmentation, dynamic strength and strain rate, granite, sandstone and limestone specimens were chosen and tested on large-diameter split Hopkinson pressure bar (SHPB) equipment with half-sine waveform loading at the strain rates ranging from 40 to 150 s−1. With recorded signals, the energy consumption, strain rate and dynamic strength were analyzed. And the fragmentation behaviors of specimens were investigated. The experimental results show that the energy consumption density of rock increases linearly with the total incident energy. The energy consumption density is of an exponent relationship with the average size of rock fragments. The higher the energy consumption density, the more serious the fragmentation, and the better the gradation of fragments. The energy consumption density takes a good logarithm relationship with the dynamic strength of rock. The dynamic strength of rock increases with the increase of strain rate, indicating higher strain rate sensitivity.
作者：
Li Wenbin*;Pan Qinglin;Zou Liang;Liang Wenjie;He Yunbin;...
期刊：
稀有金属(英文版),2009年28(1):102-106 ISSN：1001-0521
通讯作者：
Li Wenbin
作者机构：
[Pan Qinglin; Li Wenbin; Liang Wenjie; Zou Liang; He Yunbin; Liu Junsheng] Cent S Univ, Sch Mat Sci & Engn, Changsha 410083, Hunan, Peoples R China.;[Li Wenbin] Hunan City Univ, Dept Civil Engn, Yiyang 413000, Peoples R China.
通讯机构：
[Li Wenbin] C;Cent S Univ, Sch Mat Sci & Engn, Changsha 410083, Hunan, Peoples R China.
摘要：
Five kinds of Al-Zn-Mg-Cu-Zr based alloys with different Sc additions were prepared by ingot metallurgy. The effects of minor Sc on the microstructure and mechanical properties of Al-Zn-Mg-Cu-Zr based alloys were investigated using tensile tests, optical microscopy (OM), and transmission electron microscopy (TEM). The results show that the ultimate tensile strength and yield strength are improved by 94 and 110 MPa, respectively, and the elongation to failure remains at a reasonable extent (11.1%) in the Al-Zn-Mg-Cu-Zr based alloy with 0.21 wt.% Sc addition after solution heat treatment at 475°C for 40 min and then aged at 120°C for 24 h. The addition of minor Sc induces the formation of Al3(Sc,Zr) particles, which are highly effective in refining the cast microstructures, retarding recrystallization, and pinning dislocations. The increment of strength is attributed mainly to fine grain strengthening, precipitation strengthening of Al3(Sc,Zr) particles, and substructure strengthening.
作者：
Li Wen-bin;Pan Qing-lin*;Liu Jun-sheng;Liang Wen-jie;He Yun-bin;...
期刊：
中南大学学报(英文版),2009年16(4):530-534 ISSN：2095-2899
通讯作者：
Pan Qing-lin
作者机构：
[Liu Jun-sheng; Pan Qing-lin; Liang Wen-jie; Li Wen-bin; Liu Xiao-yan; He Yun-bin] Cent S Univ, Sch Mat Sci & Engn, Changsha 410083, Peoples R China.;[Li Wen-bin] Hunan City Univ, Dept Civil Engn, Yiyang 413000, Peoples R China.
通讯机构：
[Pan Qing-lin] C;Cent S Univ, Sch Mat Sci & Engn, Changsha 410083, Peoples R China.
关键词：
Al-Zn-Cu-Mg-Sc-Zr alloy;hot deformation;flow softening;microstructural evolution;activation energy
摘要：
The deformation behavior of a new Al-Zn-Cu-Mg-Sc-Zr alloy was investigated with compression tests in temperature range of 380–470 °C and strain rate range of 0.001–10 s−1 using Gleeble 1500 system, and the associated microstructural evolutions were studied by metallographic microscopy and transmission electron microscopy. The results show that true stress—strain curves exhibit a peak stress, followed by a dynamic flow softening at low strains (ɛ<0.05). The stress decreases with increasing deformation temperature and decreasing strain rate, which can be represented by a Zener-Hollomon exponential equation with the activation energy for deformation of 157.9 kJ/mol. The substructure in the deformed specimens consists of few fine precipitates with equaixed polygonized subgrains in the elongated grains and developed serrations at the grain boundaries. The dynamic flow softening is attributed mainly to dynamic recovery and dynamic recrystallization.
