西南交通大学学报

Simplified Calculation Research on Effects of Dynamic Amplification on Soft-Upper-Rigid-Down Hybrid Structures

XIONG Haibei, CHEN Lin, WU Ying, JIA Guocheng

2018, 53(2): 219-225. doi: 10.3969/j.issn.0258-2724.2018.02.001

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Abstract:
Soft-upper-rigid-down hybrid structures are more susceptible to the "whipping effect". Considering the effects of stiffness and mass ratios on the dynamic characteristics of structures, a simplified calculation method which can be used in engineering to determine the effects of dynamic amplification on a soft-upper-rigid-down hybrid structure is given by proposing the concept of a stiffness mass integrated ratio and assuming that the damping ratios of the superstructure and substructure are equal. Analysis reveals that the results of the simplified calculation method correlate well with one set of published shaking table test data and the mode-superposition method. For light wood-concrete structures, which are composed of two layers ("1+1" system), three layers ("1+2" system) or six layers ("2+4" system), the results of the simplified calculation method are in good agreement with the mode-superposition method with an error lower than 20%, which verifies the validity and reliability of the simplified calculation method. It is proposed that the simplified calculation method can be used to calculate the effect of dynamic amplification of soft-upper-rigid-down hybrid structures when the stiffness ratio of the structure is not less than 7.

Evaluation of Wind Pressure Distribution for Large-Span Warpage Roof via Wind Tunnel Testing and Numerical Simulation

LIN Yongjun, SHEN Yanchen, LI Mingshui, LUO Nan

2018, 53(2): 226-233. doi: 10.3969/j.issn.0258-2724.2018.02.002

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In order to determine the wind pressure distribution characteristics of a large-span warpage roof structure, a wind tunnel test and numerical simulation were carried out for a large-span warpage roof. First, the distribution of roof pressure and influence of open doors and windows on the wind pressure distribution were analysed according to the wind tunnel test results. Then, the mean wind pressure distribution for the roof structure was simulated on a CFX software platform by using an RNG k-ε turbulence model, and the simulation results were compared to the wind tunnel test data. The results showed that the open doors and windows yielded little influence on the external wind pressure, and non-negligible influence on the internal pressure. Specifically, when the doors and windows of one side were opened, the roof was subjected to an upward lifting force. Alternatively, when both sides were opened at the same time, the internal pressure resulted in a downward suction on the roof. The RNG k-ε turbulence model was used to simulate the average wind pressure distribution of a large-span warpage roof structure, and was found to accurately reflect the actual wind pressure. The primary effect of wind pressure on the roof was suction, and the most unfavourable position of wind load occurred at the warping edge and in the rooftop area. When the flow direction occurred parallel to the warp direction, the wind flow yielded increased separation on the warp edge and a stronger vortex on the warp surface. Wind flowing around the building resulted in the separation and vortex occurring along both sides in the flow direction; additionally, two large symmetric trailing vortexes were formed on the leeward sides. However, there was no significant evidence of separation and vortex occurring on both sides when the wind flow was directed against warpage.

Energy-Based Analysis of Anti-Seismic Performance of Latticed Shell in Coordination

ZHANG Ming, ZHOU Guangchun, ZHANG Keyue, JIA Hongyu, LI Lanping, ZHANG Deyi

2018, 53(2): 234-243. doi: 10.3969/j.issn.0258-2724.2018.02.003

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An analytical numerical model was rebuilt to reveal changes in local stress state in a single-layer reticulated shell under earthquake, as well as the relationship between the changes and structural failure loads. The numerical model was rebuilt based on the strain energy from nonlinear response history analyses at increasing levels of ground motion intensity to systematically study the redistribution of seismic internal force in elements in the single-layer reticulated shell by using the strain energy parameter. The results showed that elements in a single-layer shell can bear seismic loads harmoniously and steadily in the normal working state. However, harmonious and steady characteristics were not observed in the failure state. Therefore, different stress states can be distinguished by checking the structural coordinative working capability. In addition, the strain energy in the lower parts of the single-layer reticulated shell was larger than that in other parts such as in the radial members under horizontal ground motion, the maximum value was observed in the fifth hoop, which was 13 times larger than that in the first hoop. The strain energy in the upper parts of the single-layer reticulated shell was larger than that in other parts such as in the radial members under 3D ground motion; the maximum value was observed in the second hoop, which was 15 times than that in the sixth hoop.

Construction Control System for Thousand-Meter-Scale Hybrid Girder Cable-Stayed Bridge Based on Double Target Control

XIE Mingzhi, YANG Yongqing, BU Yizhi, ZHAO Canhui, ZHANG Keyue, WANG Xuewei

2018, 53(2): 244-252, 321. doi: 10.3969/j.issn.0258-2724.2018.02.004

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To ensure the construction control of thousand-meter-scale hybrid girder cable-stayed bridges for high efficiency, precision, and safety, taking the Edong Yangtze River Bridge as a case study, research on the construction monitoring concept, monitoring method, and monitored parameters of the super-long-span hybrid girder cable-stayed bridge was carried out, and the construction control system for this complicated structure was built. The research and the system were based on theoretical studies, finite element numerical calculations with full consideration of the structural nonlinear geometrical effects, and the issues faced at the construction site. First, according to the construction control characteristics, problems, and challenges of thousand-meter-scale hybrid girder cable-stayed bridges, the double target control system was built based on the geometry control method. Then, focusing on the key aspects of this control system, some important issues such as the determination of the initial unstressed state amount, calculations pertaining to key construction members, fabrication and cast-in-site control stage, erection stage, and safety control in the construction stage were extensively studied, and the calculation and installation control methods were obtained. Finally, the entire construction control procedure for the Edong Yangtze River Bridge was carried out using this control system. The results show that the maximum alignment error at the top of girder is 16 mm, the axis error is 2.7 mm, and the cumulative girder error is 10.8 mm during the manufacturing stage. The minimum value of the nonlinear stability safety factor is 2.5 and meets the specifications. Meanwhile, the maximum alignment error of concrete girder in the side span is 11 mm, and the maximum alignment error of the steel box girder in the middle span is 157 mm. The relative error of the pylon deviation is L/12434. Furthermore, the maximum cable force error of a single cable located in the concrete girder is 4.5%, and the maximum cable force error of a single cable located in the steel girder is 6.30%. All the analyses show that the stress condition in the entire structure is reasonable, and all the monitoring indexes meet the specifications.

Corrosion Rate of Non-Galvanized High-Strength Steel Wires under Different Temperature and Humidity Conditions

CHEN Xiaoyu, TANG Maolin

2018, 53(2): 253-259. doi: 10.3969/j.issn.0258-2724.2018.02.005

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This study helps to calculate the corrosion of steel wires of the main cable under different temperature and humidity conditions. The temperature and humidity conditions of the corrosive environment in which the main cable was placed were divided into five levels. Orthogonal experimental was conducted in this study. The corrosion rate of non-galvanized steel wires was measured by micro-polarization resistance corrosion sensors. The temperature and humidity conditions were controlled by a constant chamber. The experimental results provided the primary and secondary relation among temperature, humidity and corrosion rate. The results also provided the regression equation of the corrosion rate of non-galvanized steel wire under varying temperature and humidity conditions through regression fitting. On the basis of the corrosion rate results, corrosion areas were classified into three areas, weak corrosion area for humidity of 70% and temperature below 10℃. Low corrosion area for humidity below 75% and temperature of 20-50℃. Strong corrosion area for humidity of 75% or more and temperature of 10-50℃.

Distribution Characteristics of Welding Residual Stress at U Deck-to-Rib Connection Detail of Steel Box Girder

CUI Chuang, BU Yizhi, LI Jun, ZHANG Qinghua

2018, 53(2): 260-265. doi: 10.3969/j.issn.0258-2724.2018.02.006

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This study aimed to research the influence of residual stress on fatigue resistance at the deck-to-rib weld joint of steel box girder. Research on distribution characteristics of the field of residual stress is a precondition to verifying the influence on fatigue resistance. The study was conducted taking Hong Kong Zhuhai Macao Bridge as an example to simulate the entire welding process and the distribution of residual stress. The influence of panel thickness on residual stress was analysed. Then, empirical formulae for the residual stress distribution were proposed. The results indicate that the variation of residual stress fields can be simulated accurately using numerical methods, i.e. ANSYS thermal-structural analysis. The panel thickness has little influence on the peak residual stress at the local weld zone, and the peak transverse residual stress is approximately 300 MPa. The residual stress distribution across the thickness of the deck is in good agreement with the sinusoidal distribution, which implies that considering sine function as the empirical distribution model is feasible.

Research of Calculation Method for Wave Forces Acting on Large-Scale Bridge Piers Based on Diffraction Theory

DENG Shasha, SHEN Huoming, LIU Lang, TANG Huaiping

2018, 53(2): 266-271. doi: 10.3969/j.issn.0258-2724.2018.02.007

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In order to make the MacCamy diffraction theory applicable to calculate the wave forces on large-scale bridge piers, a calculation method was analytically and numerically investigated. First, the effects of the cross-section dimension and cross-section shape on the bridge pier inertial force coefficients were numerically examined. Then, the diffraction coefficient was introduced into the Morison equation, making the classical Morison applicable to calculate the wave forces on large-scale structures. The results show that the initial force coefficient of the square cross-section pier decreases faster, and the large-scale effects are more obvious in square cross-section piers than in the circular cross-section piers. The analytical solutions obtained from the Morison equation with a diffraction coefficient are very close to the numerical solutions. When the longitudinal wavelength is 0.2 times the wavelength, the wave forces on the large-scale square piers calculated from the modified Morison equation agree well with the numerical results.

Simplified Method for Analysing Pile-Supported Embankment Settlements over Soft Soil

LIU Feicheng, ZHANG Jianjing, YAN Shijie

2018, 53(2): 272-278. doi: 10.3969/j.issn.0258-2724.2018.02.008

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A method for the settlement of pile-supported embankments over soft soil with due consideration of soil arching and pile-soil interactions is proposed. Traditionally, settlements comprising composite foundations and built under embankments are usually divided into two parts-reinforced and un-reinforced. However, when calculating the settlements, some assumptions which are somewhat disaccordance with the truth are made. In addition, some parameters employed in some traditional methods are uncertain and the nonuniformity of layered site is hardly to be considered. Therefore the access to a more accurate analytical results is restricted.Based on the arching model proposed by Hewlett and Randolph, a uniform coefficient has herein been incorporated to allow for evaluation of non-uniform vertical stresses acting on the soft ground. This, in turn, serves to deduce solutions for the arching effect in square and triangular pile configurations. In the method proposed, the load acting on the pile head and the resulting subsoil reaction could be evaluated through analysis of the soil-arching effect. The load at the pile tip can be calculated by employing the spherical cavity expansion theory. Subsequently, additional stresses induced by the load at the pile tip, subsoil reaction, and skin friction acting on the pile could be obtained through use of revised Mindlin's solution by considering the ground to be comprised of multi-layered soil. Settlement results, obtained by accounting for additional stresses, could then be calculated using the layer-wise summation method. Settlements of the pile head and ground surface could, thus, be evaluated by superimposing different partial settlements. The proposed method serves to analyse pile-head as well as ground-surface settlements and offers the advantage that the parameters employed in the analysis could be conveniently adopted and that the deduction procedure is concise. Comparison of results obtained using the proposed method with observed data and numerical results demonstrates that the proposed method is capable of accurately estimating the settlement of piles as well as ground surface of pile-supported embankments with only a slight deviation that varies from 5.0% to 14.4%, which is an acceptable value by engineering standards.

Field Comparative Experiments of Pipe Pile Composite Foundation with Different Cushion Layers

SHAO Guoxia, SU Qian, YING Zihong, LI Ting, XIE Kang, CAO Zhengguo

2018, 53(2): 279-285. doi: 10.3969/j.issn.0258-2724.2018.02.009

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In order to compare the stress and evaluate the ability to control deep soft soil settlement of three kinds of composite foundations, field experiments were carried out. Each pipe pile composite had a different cushion layer; a reinforced concrete slab, a geocell, and a geogrid, respectively. For the geocell and geogrid composites, a pile cap was added.Both the stress response, and the settlement, of the pipe pile composite foundations, under different cushion layers, were analyzed. The results show that the stress of both the pile's top surface and the soil between the piles was gradually reduced, from the subgrade center to the shoulder. The pile-soil stress ratios were 2.47-5.42, 2.30-6.25, 8.05-14.81 for the geogrid-reinforced cushion layer, the geocell-reinforced cushion layer, and the reinforced concrete slab cushion layer, respectively. As the load of the subgrade filling increased, the tensile strength of both the geogrid and the geocell gradually increased, and maximum tension occurred at the shoulder. The tensile strength of the geocell was greater than that of the geogrid, under the same load. The composite foundation of a pipe pile, plus a reinforced concrete slab is the best for controlling the settlement of the subgrade filling, and the settlement of the ground surface contributes 68.46% and 72.56% of entire settlement of the pipe pile-pile cap-geogrid and the pipe pile-pile cap-geocell composite foundations, respectively.

Physical and Mechanical Properties of Mud Pumping Soils in Railway Subgrade Bed

NIE Rusong, LENG Wuming, SU Yu, GUO Yipeng

2018, 53(2): 286-295. doi: 10.3969/j.issn.0258-2724.2018.02.010

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Substantial increase in train speed and axle load may result in an increase in the probability of occurrence of the mud pumping problem in subgrade bed. In this study, to further study the mechanisms and occurrence conditions of the mud pumping problem, more than 60 mud pumping samples reported in published literature were studied systematically. Further, the physical and mechanical properties of mud pumping soils, such as particle composition, plasticity index, permeability, and mineral composition were analysed and summarized. The results indicate the following:For the most mud pumping soils, clay and silt particle content is greater than 20%; soils with clay content greater than 30% and silt content greater than 40% account for the largest proportion of the samples. In mud pumping soils, the silt content is generally greater than the clay content. The liquid limit is more than 23%, and plasticity index greater than 6.5, i.e., sandy clay, silty clay, clay and part of low liquid limit silty clay. Generally, the permeability coefficient of mud pumping soils is less than 1.0×10^-5 m/s. The permeability coefficient and fine particle content show good negative exponential correlation.

Evolutionary Characteristics of Pore Structure of Fly Ash Shotcrete

ZHANG Junru, WEN Yumin, OU Xiaoqiang

2018, 53(2): 296-302. doi: 10.3969/j.issn.0258-2724.2018.02.011

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To study the mixture ratio of pore structure in fly ash shotcrete during operation, low-field magnetic resonance imaging technology was adopted. The micro-pore structure of the modified cementitious shotcrete with different fly ash content was investigated. The micro-pore size distribution characteristics and porosity of shotcrete with different fly ash content, at different curing phases were measured. The results show that the porosity of the fly ash shotcrete increases with an increase in the fly ash content; however, with increase in the curing age, the porosity generally decreases first, and subsequently tends to be stable. The results also indicate that the value of porosity is minimum and maximum when the amount of fly ash is 10% and 0, respectively. After the 7-day healing period, the inner pore radius of shotcrete varies from 1 to 80 nm for different proportions of fly ash. In such a radius range, the value of micro-pore is 80% of the total fissure value. The most probable pore radius is approximately 12 nm.

Test on the Stability of Soft Rock Tunnel with High Ground Stress Field Influenced by Direction of Maximum Horizontal Principle Stress

DAI Cong, HE Chuan, XIA Wuyang, LI Shiqi

2018, 53(2): 303-311. doi: 10.3969/j.issn.0258-2724.2018.02.012

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In order to study the influence of the principal stress in a high ground stress field on the stability of surrounding rock in soft rock tunnels, a completely self-developed test system "3D geotechnical model test system for tunnels" was used to conduct the large-scale three-dimensional geological mechanics model test. In this research, the stability of surrounding rock in soft rock tunnels under two conditions, when the maximum horizontal principal stress is parallel and perpendicular to the tunnel axis, was investigated. The results show that when the maximum horizontal principal stress is parallel to the tunnel axis, the final values of vault settlement and horizontal convergence of the arch foot are -0.221 and -0.454 m, respectively; and the values of surrounding rock pressure at the vault, left arch foot, right arch foot, and invert are 0.478, 0.361, 0.416, and 0.261 MPa, respectively. When the maximum horizontal principal stress is perpendicular to the tunnel axis, the final values of the vault settlement and horizontal convergence of the arch foot are -0.309 and -0.548 m, respectively; and the values of surrounding rock pressure at the vault, left arch foot, right arch foot, and invert are 0.579, 0.652, 0.593, and 0.327 MPa, respectively. In both cases, the minimum values of the surrounding rock pressure are observed at the invert while the maximum values of the surrounding rock pressure are observed at the wall foot; the radial strain increment in surrounding rock is tensile, and tangential strain increment is compressive, indicating that the excavation of the tunnel leads to a decrease in radial stress and an increase of tangential stress.

Face Stability Analysis of Shield Tunnel in Sandy Ground Using 3D DEM

WANG Jun, LIN Guojin, TANG Xie, HE Chuan

2018, 53(2): 312-321. doi: 10.3969/j.issn.0258-2724.2018.02.013

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Based on the model test carried out by Chambon and Corte, the three-dimensional discrete element method (3D DEM) was used to study the face stability of shallow shield tunnels in sand, and the face failure mechanism was investigated from microscopic perspectives. A three-dimensional flexible stress boundary was implemented in the numerical model, and the support provided by air or fluid in the chamber for a tunnel face was simplified as specified normal pressure acting on face particles. Pressure was decreased gradually to 0 kPa, and ground deformation was closely recorded. Thus, the limit support pressure could be determined naturally. The tunnel excavation process was incorporated by deleting the particles that flowed into the tunnel, and its effect on tunnel stability was considered. Results show that when C (tunnel buried depth)/D (tunnel diameter) ≤ 1.0, the limit support pressure first increases with buried depth and then tends to be constant. The ratio of the limit support pressure to the initial support pressure decreases with buried depth. The support pressure at which ground settlement accelerates abruptly is smaller than the limit support pressure. The failure zone directly propagates up to the ground surface. In engineering practice, attention should be paid to the ground surface settlement and limit support pressure to keep the tunnel face safe. When C/D ≥ 2.0, a stable soil arch exists above the tunnel crown and extends upwards to approximately 0.7D-1.3D and 0.9D-2.3D.

Numerical Analysis of Effect of Jacked Pile on Performance of Buried Pipes

WANG Jiayong, XIAO Chengzhi, HE Chenxi

2018, 53(2): 322-329. doi: 10.3969/j.issn.0258-2724.2018.02.014

[Abstract](518)

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To analyse the influence of the driving process of jacked piles on the performance of adjacent buried pipes via the planar finite element method numerical simulation based on the displacement penetration method and achieve the dynamic pile driving process by establishing the pile-soil and pipe-soil contact surfaces and applying the displacement load at the top of the pile, comprehensive analysis was carried out to investigate the effect of the pile penetration depth, pile diameter, horizontal centre distance between the pile and buried pipe, and buried depth, on the performance of buried pipes during pile driving. The calculation results showed that when keeping other parameters identical and first increasing the horizontal distance, caused a decrease in the horizontal displacement, radial deformation, and stresses of pipes. The maximum horizontal stress of the soil surrounding the pipes is 1.5 times that of the soil without pipes. Secondly, with the increase in the pile penetration depth, there exists a critical penetration depth, after reaching it, the horizontal displacement of pipes increases significantly, then somewhat decreases, and finally becomes steady. Moreover, the maximum horizontal displacement of pipes can be reached when the penetration depth is equal to 2 times the buried depth of the pipe. Thirdly, increasing the buried depth of the pipe results in remarkable change in the deformation and mechanical performance of the pipes. For a buried depth of 5 times the diameter of pipe, the maximum horizontal displacement of the pipes reduced by 27.8% when the pile diameter decreased by 25%. This implied that reducing the diameter of jacked piles can considerably weaken its effect on buried pipes.

Study of Bedrock Surface Effect under Different Percentages of Rock

SUN Yongshuai, HU Ruilin

2018, 53(2): 330-336. doi: 10.3969/j.issn.0258-2724.2018.02.015

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The laws of deformation and failure of soil and rock mixtures under different percentages of rock were analyzed in this study, while considering the percentage of rock of the bedrock surface effect. Firstly, the intersection angle of bedrock surface and shearing surface was studied using an in-house developed large shear test. The maximum shearing stress change law was studied under different percentages of rock. The change laws of the pore water pressure and earth pressure were studied using the pore water pressure gauges and earth pressure gauges. The results showed that the shearing strength of the soil and rock mixtures increased under the same shearing displacement as the percentage of rock increased from 10% to 50%, the intersection angle of bedrock surface and shearing surface increased by 80%; the distance of the bedrock surface and shearing surface increased by 63.6% at the bottom of the bedrock surface as the percentage of rock increased; the maximum shearing stress increased by 32.5% as the percentage of rock increased; the time increased by 78.9% when the pore water pressure change value reached the corresponding maximum value as the percentage of rock increased. The time increased by 80% when earth pressure change value reached the corresponding maximum value as the percentage of rock Increased. The rock rotated, but the remained undamaged. The rock pointed to the shearing failure direction of soil and rock mixtures.

Geostress Field Analysis of Futang Tunnel, before and after Wenchuan Ms8.0 Earthquake

LI Tianbin, CHEN Guoqing, YAN Jun, LUO Kai

2018, 53(2): 337-343. doi: 10.3969/j.issn.0258-2724.2018.02.016

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After an earthquake, such as the "5.12 Wenchuan earthquake", some of the high stresses in the hanging wall of seismic faults should be released. However, the rock mass surrounding the Futang Tunnel, is still under high stress, even after the earthquake, as evidenced by rockburst and core cracking. To investigate this issue, in-situ stress tests and back analysis of the tunnel's regional stress field, before and after the earthquake, were conducted to deduce the formation mechanism of this high stress. Research shows that the high stresses are produced by the integration of the continuous effects of fault thrusts, epigenetic and superficial reformation, medium differences, the effect of distance to the fault, and so on. The stress on the Yingxiu side of the Futang Tunnel decreased significantly after the earthquake, but on the Wenchuan side, there was little decline, and so the stress is still high. The maximum stress in Section K18+850-K21+450 is between 20-25 MPa. This unique stress distribution means that both sides of the tunnel require different engineering features, and have important engineering consequences for the design of support parameters, the construction method and the construction cost in different tunnel sections.

GPS Derived Evolution of Strain Rate in Sichuan Region

XU Rui, D. Sarah·Stamps, HUANG Shengmu

2018, 53(2): 344-350. doi: 10.3969/j.issn.0258-2724.2018.02.017

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To study the impact of the Wenchuan earthquake on the stress re-distribution and corresponding seismic potential of the southeastern Tibetan Plateau and Sichuan Basin, In this study, 355 GPS sites in the Sichuan region of the southeastern Tibetan Plateau were used to calculate 4 sets (1997-2008, 2009-2011, 2011-2013, and 2013-2015) of GPS velocity fields for the period 1997-2015. These velocity results were used to deduce the corresponding dilatation, vertical rotation, and maximum shear strain rates, based on regular grid and splined interpolation methods. Subsequently, taking the 2008 Ms8.0 Wenchuan earthquake as the primary reference point and the subsequent 2013 Ms7.0 Lushan and 2014 Ms6.3 Kangding earthquakes as secondary reference points, the spatial and temporal evolution of the aforementioned strain rates and their relationships with the seismic events were analyzed. The results indicate that all types of strain rates, both in space and time, taper off along the Longmen Shan Fault with the passage of time after the Wenchuan earthquake. However, they have not yet recovered to their pre-seismic status, which implies that post-seismic relaxation of the Wenchuan earthquake is now dominated by ductile flow in the lower crust. The dilatation strain rate of the area enclosed by the Anninghe and Zemuhe faults shows an increase after the Wenchuan earthquake. This reveals the seismic hazard faced by the region and further detailed studies are required here. The location of maximum vertical rotation strain rate seems to transfer from the southern segment of the Xianshuihe fault to the Anninghe and Zemuhe faults, and even further southward to the Xiaojiang fault. However, the magnitude of this transfer is so small that detailed further studies are required to ascertain whether this transfer is realistic and the implications it bears, if so. The maximum shear strain rate indicates that the Daliang Shan sub-block and the northern segment of the Xianshuihe fault are still regions with high level seismic risk, and these should be the focus of future studies.

Robust Control of the Air Conditioning System of an Electric Vehicle with Actuator Fault

HU Guangdi, WANG Guohui, LUO Huiyu, ZHOU Ke, LANG Xiaoyue

2018, 53(2): 351-358. doi: 10.3969/j.issn.0258-2724.2018.02.018

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This paper is concerned with the development of an actuator fault model in the process of operation of electrical vehicle air conditioning system and the design of a state observer to observe the state of this system. Then established the uncertain system of air conditioning system based on linear matrix inequalities to design a state feedback H_∞ robust controller that can compensate for the actuator fault of an automobile air conditioning system and stabilize the controller. The state feedback controller is designed through simulation experiments under trouble-free and faulty modes. The observation error under each mode was 0.1% and 0.6%, which satisfied the demand of system observation, compared with the air conditioner H_∞ controller, which does not consider actuator failures. The state feedback controller could effectively suppress jamming at medium frequencies and frequencies lower than 10 Hz. Finally, the control strategy is verified by simulating a closed-loop system using the two types of controllers.

Diagnostic Method for High-Speed Train Bearing Fault Based on EEMD-TEO Entropy

JIN Hang, LIN Jianhui, WU Chuanhui, DENG Tao, HUANG Chenguang

2018, 53(2): 359-366. doi: 10.3969/j.issn.0258-2724.2018.02.019

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To overcome the limitations of the between-class separateness of low-frequency signals of high-speed train bearing faults as well as the problem of fault identification of the cage, an adaptive diagnostic method based on the Teager energy operator (TEO) and ensemble empirical mode decomposition (EEMD) entropy is proposed. This method combines the EEMD, sample entropy, and the TEO, and the intrinsic mode function (IMF) signal is obtained by the self-adaptation of EEMD, and then the sample entropy is obtained from the IMF using the improved TEO. Finally, the support vector machine (SVM) is used to determine the working state and fault type of the bearing. The fault eigenvectors of the EEMD energy entropy, EEMD singular value entropy, EEMD-TEO time-frequency entropy generation, and the identification results of this vector in the SVM are discussed. The method was used to diagnosethefault ofbearingsviathedata in three states:normal bearing, retainer bearing, and fault of the rolling body. The results show that the fault recognition rate for the three bearing states can reach 98%, increased by 2.6% compared to the traditional empirical mode entropy, this method can be used for the diagnosis of high-speed train bearings.

Temperature Compensation of Maglev Vehicle Gap Sensor Based on RBF-NN Optimized by PSO

JING Yongzhi, HE Fei, LIAO Haijun, WANG Ying, LIU Guoqing, DONG Jinwen

2018, 53(2): 367-373, 384. doi: 10.3969/j.issn.0258-2724.2018.02.020

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In order to solve the temperature drift problem of a maglev vehicle gap sensor, a temperature compensator based on RBF-NN (radial basis function neural network) was designed to compensate the temperature drift error. A hybrid algorithm was proposed to combine PSO (particle swarm optimization) algorithm with gradient descent algorithm. In the proposed algorithm, the global optimal particle of the PSO was optimized by the gradient descent method. The hybrid algorithm has stronger optimization ability. The compensation model was optimized by the hybrid algorithm and the accuracy of the compensation model was considerably improved. Finally, the compensation model was implemented in FPGA (field-programmable gate array). Experimental results show that temperature drift error of the gap sensor can be compensated effectively. The compensated output of the gap sensor was independent of the temperature. The gap sensor provides correct gap data with a maximum error of 0.45 mm for full scale and a maximum error of 0.16 mm for a working gap from 8 mm to 12 mm.

Development of Overmoded Coaxial to Two-Way Rectangular Waveguide Power Divider

ZHANG Jianqiong, LIU Qingxiang, LI Xiangqiang, LIANG Yuan, MEN Manzhou

2018, 53(2): 374-377. doi: 10.3969/j.issn.0258-2724.2018.02.021

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Abstract:
To achieve the high-efficiency mode conversion of an overmoded coaxial waveguide to a two-way rectangular waveguide in high power microwave systems, an overmoded coaxial waveguide for two-way rectangular waveguide power divider is researched. The divider uses the radial line as a mode transition structure from a coaxial waveguide to a rectangular waveguide. First, the coaxial waveguide TEM mode is divided into four rectangular waveguide TE₁₀ modes; then the four rectangular waveguides are combined into two paths, which effectively inhibit the generation of high-order modes in the overmoded waveguide and achieve a high power-handling capacity and transmission efficiency. The design and experiment results show that at a central frequency of 2.88 GHz, the VSWR of the power divider is approximately 1.04, the corresponding transmission loss of the TEM mode to the TE₁₀ mode is 0.15 dB, the output imbalance is approximately 0.15 dB, and the power capacity of the design is 4.52 GW, which can satisfy the needs of high-power applications.

Impact of Interacted Hazardous Actions on Injury Severity in Both-at-Fault Crashes

JIANG Xinguo, ZHANG Guopeng, SHI Xiaolin, XIA Liang, JIA Xiongwen

2018, 53(2): 378-384. doi: 10.3969/j.issn.0258-2724.2018.02.022

[Abstract](403)

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Abstract:
In order to understand the relationship between interacted hazardous actions and the injury severity in both-at-fault crashes, and alleviate the crash injury from the perspective of driving behaviour, the generalized ordered logit model was adopted by combining the characteristics of both-at-fault crashes and the applicability of each statistical model. This enabled the identification of the effects of the interaction of various dangerous driving behaviours on the severity of both-at-fault crashes. In addition, the influence of dangerous driving on the severity of injuries was also analysed. The results indicated that the effects of both drivers driving left of centre, driving carelessly, speeding and failing to yield, speeding combined with reckless driving and failing to yield, and disobeying traffic rules increased the possibility of severe injuries. The analytic results indicated the need for enhancing driving education programs to promote safe driving, and monitoring hazardous actions using technological tools such as monitoring speed limits and employing electronic police systems.

Dynamic Robertson's Platoon Dispersion Model in Connected Vehicle Environment

YAO Zhihong, JIANG Yangsheng

2018, 53(2): 385-391. doi: 10.3969/j.issn.0258-2724.2018.02.023

[Abstract](455)

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Abstract:
The parameters of the traditional Robertson's platoon dispersion model are based on historical data, and thus, it cannot provide a good reflection of the dynamic characteristics of traffic flow. In order to solve this problem, a connected vehicle environment is considered, and the travel time of the vehicles is easily obtained. The relevant parameters of the Robertson's model can be estimated in real time based on this. Then, a dynamic Robertson's platoon dispersion model was proposed. Later, the relationship between the arrival flow rate of the downstream intersection and the departing flow rate of the upstream intersection was analysed using the proposed model with field collected data, and compared with those obtained using the traditional Robertson's model and actual data. The results show that the proposed model can better describe the law of dispersion in traffic flow, and the mean squared error of prediction is reduced by approximately 30.68%, compared with the traditional Robertson's model.

Optimal Order Decision Making for Fresh Agricultural Products Delivered by High-Speed Railway

QIU Ge, WU Sheng

2018, 53(2): 392-399. doi: 10.3969/j.issn.0258-2724.2018.02.024

[Abstract](435)

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Abstract:
In the context of the fast speed of high-speed rail express transportation and the perishability of fresh agricultural products, this study constructed an optimal order decision-making model for the supply chain of fresh agricultural products. The exponential function model is proposed to measure the decay of fresh agricultural products' freshness with transportation time. Considering the difference between high-speed rail transportation and ordinary transportation in terms of unit transportation cost and transportation time, the necessary conditions for supply chain leaders to choose high-speed rail express were quantitatively analyzed under two decision-making modes:supplier-dominated and retailer-dominated. The research shows that there is an optimal pricing and ordering strategy for the supply chain of fresh agricultural products transported by high-speed rail. The supplier is more sensitive to the per unit transportation cost of the high-speed rail than the retailer. The maximum expected profit of a supply chain is a monotonically decreasing function of the freshness of fresh agricultural products and the price elasticity coefficient.

Flight Level Allocation Optimization to Reduce Greenhouse Effect

TIAN Yong, WAN Lili, YE Bojia, WANG Zhongfengyan

2018, 53(2): 400-405. doi: 10.3969/j.issn.0258-2724.2018.02.025

[Abstract](429)

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Abstract:
To reduce the regional environmental impacts of air traffic flow, this study investigated a green trajectory optimization method for reducing greenhouse effect. According to the characteristics of the regional sector aircraft and the flight conflict resolution method, the influences of CO₂ emissions and aircraft contrails on global surface temperature change were analysed and a regional aircraft deployment model was established to minimise the greenhouse effect. A genetic algorithm based on the elite retention strategy was designed. The feasibility of this algorithm was verified using real flight operations data of ZBAAAR02 as an example. The calculation result shows that the model can effectively reduce the rise in global temperature due to flight operations in the sector. The global surface temperature can decrease by 98.74%, 97.69%, and 97.11% in 25, 50, and 100 years respectively with this model. The results obtained suggests that flight level allocation model optimisation can effectively reduce the greenhouse effect.

Centralized Scheduling of Service Vehicles for Aircraft Turnaround Based on Partheno-Genetic Algorithm

ZHU Xinping, HAN Songchen

2018, 53(2): 406-413. doi: 10.3969/j.issn.0258-2724.2018.02.026

[Abstract](392)

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Abstract:
In order to solve the centralized scheduling problem of service vehicles for aircraft turnaround, a partheno-genetic algorithm with hierarchical encoding structure was proposed. The service activity number and vehicle number were employed to encode the control and parametric genes chromosome, respectively, which characterized the temporal and vehicle scheduling rules in turnaround service, ensuring the applicability of algorithm. The crossover and mutation operators were designed, which acted on each control genes chromosome segment and between different parametric genes chromosome segments. The schedulable capacity concept for service vehicle was introduced in chromosome decoding process to optimize search ability of algorithm. The fitness function was established to minimize the penalty of flight delay due to turnaround service and driving distance cost of vehicle, which measured the overall efficiency of turnaround service and vehicle scheduling. The data of aircraft turnaround was used to validate the proposed algorithm, and also the nearest vehicle scheduling strategy and workload balance scheduling strategy were compared. The results indicate that, the convergence of the proposed algorithm is acceptable, and flight delays in these two scheduling strategies are close, while the vehicle driving time is 40% shorter in the nearest vehicle scheduling strategy.

Graphical Processing Method of High-Speed Railway Construction Progress Data

NING Xinwen, ZHU Qing, REN Xiaochun, HAN Zujie, WANG Hua, ZHAO Wen, ZHANG Heng

2018, 53(2): 414-419. doi: 10.3969/j.issn.0258-2724.2018.02.027

[Abstract](423)

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A method for processing data by graphical construction was proposed to solve the problems pertaining to acquisition of railway construction progress data, such as a low degree of automation and standardization, complicated procedure, and coarse data granularity. The object-oriented method was first used to deconstruct the engineering structure, and parameters were extracted automatically from design construction drawings; then, a graphical construction data acquisition system was designed and developed using Web GIS, graphical filling and auditing of progress data was realized, and the progress data drove the workbench BIM model to carry out the 3D display. Subsequently, a variety of progress report files could be generated automatically by statistical analysis of progress data. The Yangda Railway Project was employed as an example to verify the validity and feasibility of the proposed method. The results show that the graphical construction progress data satisfies the requirements of project contracting, construction, and supervision for owners and other units, for the coordinated management of high-speed railway construction; reduces statistical analysis work by 70%; and significantly improves the technical standard and efficiency of project construction schedule management.

Effects of Biochar on Hydrologic Performance of Bioretention

TIAN Jing, LIU Dan

2018, 53(2): 420-426. doi: 10.3969/j.issn.0258-2724.2018.02.028

[Abstract](405)

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A pilot-scale bioretention system with 4% (w/w) biochar amendment was installed to evaluate the impact of the biochar on the bioretention in the aspects of runoff infiltration, water retention and hydraulic residence time. Hydraulic conductivity tests and three bromide tracer experiments were conducted in the pilot-scale bioretention system. Results show that:compared to the control group, the saturated hydraulic conductivity of filter medium with the biochar amendment increased by 1.5 times, the hydraulic retention time of the bioretention increased by nearly 1 h, and the volumetric water content of vadose zone increased by 11%-23%. Using the biochar can improve the hydraulic performance of the bioretention, avoid overflow, mitigate peak flow, increase water retention and reduce the discharge of runoff.

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2018 Vol. 31, No. 2