Toughness improvement mechanism and evaluation of cement concrete for road pavement:A review

Traditional cement concrete has the disadvantages of low tensile strength,poor toughness,and rapid development of cracks while cracking,which causes a significantly negative influence on the safety and durability of concrete road pavement.This paper presents a state-of-the-art review of toughness improvement mechanisms and evaluation methods of cement concrete for road pavement.The review indicates that(i)The performance of concrete material depends on its material composition and internal structure.Aggregate size,cement properties and admixtures are the main factors of concrete toughness.(ii)The incorporation of rubber or fiber in pavement concrete improves the toughness of concrete materials.However,these additions must be maintained within a reasonable range.The amount of rubber and fiber are encouraged not more than 30%of the volume of fine aggregate and 2%of the volume of concrete,respectively.(iii)The toughness of pavement concrete material includes the toughness regarding bending,impact and fracture.The toughness of cement concrete for highway and municipal pavement is generally evaluated by bending and fracture toughness,while the toughness of airfield pavement concrete is more focused on impact toughness.(iv)The toughening measures of cement concrete for road pavement are mainly mixed with rubber or fiber,while these two materials have their defects,and the application of hightoughness cement concrete in the actual road still faces many challenges.For example,the synergistic effect of rubber and fiber,the development and application of new flexible admixtures,and the formulation of the toughness index of pavement cement concrete materials need further research.

Deformation monitoring of long-span railway bridges based on SBAS-InSAR technology

The deformation monitoring of long-span railway bridges is significant to ensure the safety of human life and property.The interferometric synthetic aperture radar(In SAR)technology has the advantage of high accuracy in bridge deformation monitoring.This study monitored the deformation of the Ganjiang Super Bridge based on the small baseline subsets(SBAS)In SAR technology and Sentinel-1A data.We analyzed the deformation results combined with bridge structure,temperature,and riverbed sediment scouring.The results are as follows:(1)The Ganjiang Super Bridge area is stable overall,with deformation rates ranging from-15.6 mm/yr to 10.7 mm/yr(2)The settlement of the Ganjiang Super Bridge deck gradually increases from the bridge tower toward the main span,which conforms to the typical deformation pattern of a cable-stayed bridge.(3)The sediment scouring from the riverbed cause the serious settlement on the bridge’s east side compared with that on the west side.(4)The bridge deformation negatively correlates with temperature,with a faster settlement at a higher temperature and a slow rebound trend at a lower temperature.The study findings can provide scientific data support for the health monitoring of long-span railway bridges.

Fundamental Ideas and Basic Concepts of HSR Route Selection in Complicated Urban Areas

Up till now,no systematic studies on railway route selection in urban areas,HSR route selection in particular,have been taken in China.Based on the Shenzhen Railway Terminal Project and the Shenzhen-Shanwei Railway Project,research on HSR route selection in complicated urban areas has been conducted.An optimal route selection plan is determined after studying the local geological and environmental conditions and the complexity of tunnel construction.The research concludes that there are four major concerns in HSR route selection:the match between the new route and the urban planning,the potential economic return for the massive investment,the likely impacts of land expropriation on social stability,and the best synthesis of multiple controlling factors to meet the HSR standard.Moreover,six principles should be followed in railway route selection in complicated urban areas:the new route should be in alignment with the railway deployment;the route should align with the existing passage as much as possible;extensive analysis and in-depth demonstrations should be done to find the most appropriate combination of open and hidden excavation in tunnel construction;geological conditions and tunnel construction complexities are among the priorities;environmental sensitive sites and environmental vibration noise should be avoided as much as possible;special attention should be paid to the relocation of the power supply,television and communication facilities and the rearrangement of tubes and wires.

Research on Construction Scheme of Cloud Platform for Core Network Equipment of Railway 5G Private Network

This paper studies and analyzes the rigorous requirements of railway 5G private network core network(5GC)equipment based on network function virtualization(NFV)technology in terms of reliability,security,latency and other aspects of communication cloud,compares cloud platform schemes with different decoupling modes,and proposes that railway 5GC should be implemented by software and hardware integration scheme or software and hardware two-layer decoupling scheme.At the same time,the redundancy and disaster recovery schemes and measures that can be taken by 5GC based on cloud platform are proposed.Finally,taking the products of ZTE Corporation as an example,the implementation architecture of railway 5GC cloud platform in 1+1 redundancy mode is given.It serves as a reference for the engineering construction of 5G-R core network.

Optimization and Design of Cloud-Edge-End Collaboration Computing for Autonomous Robot Control Using 5G and Beyond

Robots have important applications in industrial production, transportation, environmental monitoring and other fields, and multi-robot collaboration is a research hotspot in recent years. Multi-robot autonomous collaborative tasks are limited by communication, and there are problems such as poor resource allocation balance, slow response of the system to dynamic changes in the environment, and limited collaborative operation capabilities. The combination of 5G and beyond communication and edge computing can effectively reduce the transmission delay of task offloading and improve task processing efficiency. First, this paper designs a robot autonomous collaborative computing architecture based on 5G and beyond and mobile edge computing(MEC).Then, the robot cooperative computing optimization problem is studied according to the task characteristics of the robot swarm. Then, a reinforcement learning task offloading scheme based on Qlearning is further proposed, so that the overall energy consumption and delay of the robot cluster can be minimized. Finally, simulation experiments demonstrate that the method has significant performance advantages.

BDS/GPS deformation analysis of a long-span cable-stayed bridge based on colored noise filtering

Combining GPS and BDS technology to monitor the deformation of long-span railway bridges with stricter deformation control requirements is of significance to the safety and control of the bridge and the safety of railway traffic.Previous studies have ignored the influence of coloured noise in the deformation time series.This is not conducive to accurate deformation analysis of long-span railway bridges.Therefore,GPS,BDS and GPS/BDS monitoring data of Ganjiang Bridge located in Ganzhou city,Jiangxi Province,China are adopted in this paper to filter the coloured noise in the deformation time series by principal component analysis(PCA),and the influence of coloured noise on the deformation analysis results of railway bridge is analysed.The experimental results show that the diurnal temperature difference causes the mid-span and the tower of the railway cable-stayed bridge to deform with a period of about one day in the vertical and longitudinal directions,respectively.Ignoring colored noise will make the uncertainty of the deformation parameter estimation overly optimistic.PCA can significantly reduce the coloured noise,and thus reduce the uncertainty of deformation parameter estimation by about 73%.Moreover,the average difference between the daily periodic motion amplitudes of the monitoring points obtained by using GPS and BDS deformation time series is 1.65 mm.The use of GPS/BDS deformation time series is not only helpful to reduce the influence of coloured noise,but also can reduce the difference between amplitude analysis results obtained from GPS and BDS deformation time series.

Combined process of sequencing batch reactor activated sludge process and constructed wetland for domestic wastewater treatment

By combining sequencing batch reactor (SBR) activated sludge process and constructed wetland (CW), this study is to achieve the domestic wastewater treatment. Our purpose was to determine the optimum operating parameters of the combined process. The process involved advantages and shortages of SBR and CW. Under normal temperature, the 3rd cycle (SBR’s operation cycle is 8 h: inflow for 1 h, limited aeration for 3 h, sediment for 1 h, outflow for 1 h, and idling for 2 h; CW’s hydraulic retention time (HRT) is 24.8 h and hydraulic loading is 24.5 m3/m2 d) was the best cyclic mode. The effluents can meet the standard GB/T18921-2002: "The reuse of urban recycling water: water quality standard for scenic environment use". In the 3rd cycle, the efficiency of CW was the maximum, and energy consumption of SBR was the minimum. Under the condition of low dissolved oxygen, the removing efficiency of chemical oxygen demand (COD) and ammonia was not affected obviously. Simultaneously, nitrification and denitrification phenomena occured and phosphorus was absorbed obviously.

Innovative Design and Development of Simplysupported Tied Arch of Beijing-Shanghai HSR

Simply-supported tied arch is a zero-thrust arch bridge with clear structural force,large stiffness,low height,beautiful appearance and economic efficiency.In Xuzhou-Shanghai section of Beijing-Shanghai HSR,the simply-supported tied arch is systematically studied and widely applied for the first time.A total of 21 simplysupported tied arch bridges with the spans of 96 m,112 m and 128 m respectively are constructed for the route.The simply-supported tied arch is an external static and internal super-static parallel arch or basket arch of Nielsen system in structure;single-box,threechamber and equal-height prestressed concrete box girder is adopted for the tie beam;dumbbell steel pipe concrete section is adopted for the arch rib;PES(FD)low-stress anticorrosion cable body is adopted for the suspender.The rational structural form is determined by comparative study on the key technical parameters such as the layout form of suspender,rise-span ratio and arch axis alignment.This paper summarizes the optimization of simplysupported tied arch structure and looks forward to the development of bridge structure.

Numerical calculation on solar temperature field of a cable-stayed bridge with U-shaped section on high-speed railway

Based on transient temperature field theory of heat conduction,the solar temperature field calculation model of U-shape sectioned high-speed railway cable-stayed bridge under actions of concrete beams and ballast was established.Using parametric programming language,finite element calculation modules considering climate conditions,bridge site,structure dimension and material thermophysical properties were compiled.Six standard day cycles with the strongest yearly radiation among the bridge sites were selected for sectional solar temperature field calculation and temperature distributions under different temperature-sensitive parameters were compared.The results show that under the influence of sunshine,U-shape section of the beam shows obvious nonlinear distribution characteristics and the maximum cross-section temperature difference is more than 21 °C; the ballast significantly reduces sunshine temperature difference of the beam and temperature peak of the bottom margin lags with the increase of ballast thickness; the maximum cross-section vertical temperature gradient appears in summer while large transverse temperature difference appears in winter.

LS-SVM and Monte Carlo methods based reliability analysis for settlement of soft clayey foundation

A method which adopts the combination of least squares support vector machine（LS-SVM） and Monte Carlo（MC） simulation is used to calculate the foundation settlement reliability.When using LS-SVM,choosing the training dataset and the values for LS-SVM parameters is the key.In a representative sense,the orthogonal experimental design with four factors and five levels is used to choose the inputs of the training dataset,and the outputs are calculated by using fast Lagrangian analysis continua（FLAC）.The decimal ant colony algorithm（DACA） is also used to determine the parameters.Calculation results show that the values of the two parameters,and δ2 have great effect on the performance of LS-SVM.After the training of LS-SVM,the inputs are sampled according to the probabilistic distribution,and the outputs are predicted with the trained LS-SVM,thus the reliability analysis can be performed by the MC method.A program compiled by Matlab is employed to calculate its reliability.Results show that the method of combining LS-SVM and MC simulation is applicable to the reliability analysis of soft foundation settlement.

The effect of track alignment irregularity on wheel-rail contact geometry relationship in a turnout zone

The irregularity is a key factor affecting the wheel-rail contact geometry relationship. In this paper, we calculated the wheel-rail contact points at typical sections and obtained the longitudinal variation of the wheel-rail geometry relationship with the trace line method. The profile of the key rail sections was matched by cubic spline curve, and the shape interpolation was realized in non-controlling sections. The results show that the roll angles at each typical section increases gradually with the enlargement of track alignment irregularity. When the flange contact occurs, the roll angle increases dramatically. Proper track alignment irregularity towards the switch rail improves the structure irregularity of the turnout.

Analysis and Research on the Thermal Environment of Subway Stations in Wuhan

With the rapid advancement of urban construction,urban subway construction in China has entered an advanced development stage and the thermal environment of subway stations has become a key factor affecting passengers'thermal comfort.To further understand the actual situation of the thermal environment of subway stations,field measurement and CFD simulation were carried out on a subway station hall in Wuhan from July to August 2021,and the thermal environment changes and influencing factors during subway operation were compared and analyzed.The present situation of the thermal environment in subway stations was analyzed,and some suggestions and measures for improving the thermal environment were put forward.

Comparison of Illuminance in Different Environments: A Case Study on Subway Stations

With urbanization and the rapid development of social economy,China’s rail transit industry has developed rapidly in recent years.In order to alleviate the pressure of road network,subways provide convenience as they are fast and space-saving.Subway stations are major energy consumers of urban power grid due to their large traffic volume and long operation time.On the premise of ensuring operation safety,reducing the energy consumption of subway helps in energy conservation and emission reduction as proposed in the 13th Five-Year Plan.According to the statistics of the energy-saving evaluation report of rail transit engineering,the lighting system accounts for 20%-30%of the total power consumption of the subway station.Due to the single lighting control mode of the lighting system in the subway station,the actual station illumination cannot be reported and adjusted in time,resulting in the waste of lighting energy and high power consumption of the system.Through in-depth research on the intelligent lighting system of subway station,this paper improves the system control,and finally summarizes the optimization scheme of subway station lighting design which can effectively save the power consumption of lighting system.The main contents of this paper are as follows:The research results of this paper can provide effective measures for energy saving of electric lighting in subway stations and reduce electric energy consumption;on the other hand,as an integral part of building lighting energy-saving system,it also has certain guiding significance for the research of building lighting energy-saving.

轨道不平顺小样本全信息表达的联合模拟方法

针对传统方法需要生成大量轨道不平顺样本才能涵盖所有随机特征,但样本数多又会导致计算效率低的问题,本文提出了一种自适应采样法(ASM)与改进的第二类随机谐和函数法(MSHF)结合的轨道不平顺模拟的联合方法。ASM自适应选取符合轨道不平顺功率谱密度函数(PSD)谱概率分布的高代表性样本点,从而减少样本数量;之后在SHF中添加一类符合谱概率分布的独立变量进行改进,通过将ASM选取的样本点代入新增变量,实现了轨道随机不平顺的时域小样本全信息表达。以车轨桥耦合系统(TTBS)随机动力分析为例,与传统一次性采样和SHF方法相比,本文方法在提高精度的同时可以减少41.67%的计算时间。

Optimization of train plan for urban rail transit in the multi-routing mode

The train plan of urban rail transit under multi-routing mode can be divided into three parts： train formation, train operation periods and corresponding train counts of each routing in each period. Based on the analysis of passen- ger＇s general travel expenses and operator＇s benefits, the constraints and objective functions are defined and the multiobjective optimization model for the train plan of urban rail transit is presented. Factors considered in the multi- objective optimization model include transport capacity, the requirements of traffic organization, corporation benefits, passenger demands, and passenger choice behavior under multi-train-routing mode. According to the characteristics of this model and practical planning experience, a three-phase solution was designed to gradually optimize the train formarion, train counts as well as operation periods. The instance of Changsha Metro Line 2 validates the feasibility and efficiency of this approach.

玄武岩纤维加筋粉质黏土力学特性的试验研究

纤维加筋技术可以显著改善土体的力学性能,在岩土工程领域得到广泛的应用。玄武岩纤维作为一种新型环保的加筋材料,其与土体的力学性能得到越来越多的关注。本文通过三轴压缩试验以及动三轴试验研究了纤维含量、含水率以及围压等因素对玄武岩纤维加筋粉质黏土剪切特性、动弹性模量以及阻尼比的影响。试验结果表明:玄武岩纤维可以通过提高黏聚力来提高粉质黏土的剪切强度,当纤维含量为0.2%、含水率为18.5%(最优含水率)时,纤维加筋粉质黏土的剪切强度最大。随着纤维含量以及含水率的增加,相同动应变对应的动弹性模量呈现先增大后减小的变化趋势,当土体的纤维含量为0.2%、含水率为18.5%时,其动弹性模量最大;动弹性模量与围压呈现正相关关系。土体阻尼比随着纤维含量以及含水率的增加先减小后增大,随着围压的增加而减小。综合分析表明,本文所采用的玄武岩纤维最优含量在0.2%左右。纤维加筋粉质黏土的扫描电镜(SEM)结果表明:单根纤维与土体间的握裹作用以及纤维网间的约束作用是加筋土强度增强的主要机理。

Frozen curtain characteristics during excavation of submerged shallow tunnel using Freeze-Sealing Pipe-Roof method

The Freeze-Sealing Pipe-Roof(FSPR)method,which has been applied for the first time in the Gongbei Tunnel of the Hong Kong-Zhuhai-Macao Bridge,is a new approach of tunnel pre-support that allows flexible adjustment of freeze tube arrangement and can be adapted to different environmental conditions.When the FSPR method is used to construct shallow burial submerged tunnels,the frozen wall to hold back groundwater during excavation will be weakened by air and water flows inside and outside the tunnel,and its waterproof performance needs to be further investigated.In this paper,a two-dimensional numerical model of the temperature field considering excavation and moving water boundary is established based on the preliminary design scheme and in-situ conditions and is used to analyze the variation in frozen curtain properties with various active freezing times during excavation.The results show that excavation has a weakening effect on both sides of the frozen wall,with a greater effect on the inner side,and a positive temperature appears in the local area inside the jacked pipe.The concrete fill in the jacked pipe obviously improves the freezing efficiency,and the tunnel excavation after 60 days of active freezing in the interval filling mode can ensure that the frozen soil thickness at the thinnest segment exceeds 2 m,i.e.,the design requirement.In practice,the active freezing time can be extended appropriately to reduce the influence of river water flow above the tunnel.The study serves as a technical reference for the design and implementation of similar projects.

Aφ6-m Tunnel Boring Machine Steel Arch Splicing Manipulator

Robotic splicing of steel arches is a challenging task that is necessary to realize the grasping and docking of steel arches in a limited space.Steel arches often have a mass of more than 200 kg and length of more than 4 m.Owing to the large volume and mass of steel arches and the high requirements for accurately positioning the splicing,it is difficult for a general manipulator to meet the stiffness requirements.To enhance the structural stiffness of the steel arch splicing manipulator,a single-degree-of-freedom(DOF)closed-loop mechanism was added to the grasping structure of the manipulator.Based on the basic principle of structural synthesis,a solution model of the single-DOF closed-loop mechanism was developed,and alternative kinematic pairs of the mechanism with different input constraints and output requirements were derived.Based on this model,a design method for a single-DOF closed-loop grasping mechanism and a posture adjustment mechanism for a steel arch was devised.Combined with the same dimensional subspace equivalence principle of the graphical-type synthesis method,12 types of steel arch splicing manipulator were constructed.By analyzing the motion/force transmission and structural complexity of the steel arch splicing manipulators,the best scheme was selected.A prototype of the steel arch splicing manipulator was manufactured.Adams software was used to obtain clearly the output trajectory of the end of the manipulator.The relative spatial positions of the upper and lower jaws under different working stages were analyzed,demonstrating that the manipulator satisfied the grasping requirements.Through a steel arch splicing experiment,the grasping effect,docking accuracy,and splicing efficiency of the manipulator met the design requirements.The steel arch splicing manipulator can replace the manual completion of the steel arch splicing operation,significantly improving the operation efficiency.

A measurable evaluation method of visual comfort in underground space by intelligent sorting and classification algorithms

Based on human perception and machine learning methods,this study proposes a measurable method for evaluating visual comfort in underground spaces.First,a comfort evaluation index based on the characteristics of human visual perception is proposed,and color features and segmentation extraction methods for intelligent methods are given.Then,using probability statistics and machine learning methods,a multi-class intelligent sorting and classification algorithm for ranking visual comfort levels is constructed and a comparison is made of the suitability of different intelligent methods for evaluating visual comfort.The random forest algorithm is then selected as the most effective measurable intelligent evaluation algorithm for underground spaces.Finally,the proposed method is compared to intelligent methods employed by previous research,and a case study,the Wujiaochang underground space in Shanghai,China,is applied as the background.Results show that the proposed method can effectively improve the quantification and refinement of human perception and evaluation of comfort in underground spaces;this method will also be useful in computer-aided generative design in the future.

Visualization aided system of hydropower engineering management

For the purpose of realizing the information visualization of hydropower engineering management,we constructed three kinds of graphics models sorted by hierarchy for system modelling,employed the construction simulation system to simulate the real-time construction behaviours,introduced the graphics rendering system to organize and update the virtual scene,and designed the interaction system to respond to the user-initiated and simulation-initiated events.So,the real-time,interactive visualization aided system of hydropower engineering management is developed.Eventually,the effectiveness and capabilities of the system are showed through the application examples in China.