Abstract:This paper reviews the hot research topic of the performance deterioration and preventive maintenance of in-service concrete bridges. As complicated structural systems, concrete bridges have characteristics of multiple causes of structural damage, complex degradation mechanisms of materials, and difficult assessment of the structural performance. Due to the combined action of the environmental and loading effects, the properties of steel reinforcement and concrete materials deteriorate, which leads to a decrease in the load-carrying capacity of the structural components and ultimately affects the structural performance of the whole concrete bridge. This paper discusses the performance deterioration and preventive maintenance of the in-service concrete bridges in many aspects, such as the material degradation mechanism, the simulations of the mechanical performance dete-rioration of materials and structures, the evaluations of service performance, the predictions of remaining service life, and the determination of preventive maintenance strategies. Meanwhile, the advantages and disadvantages of the proposed models and methods are compared and analyzed. Consequently, from different levels of materials, components and structures of the existing concrete bridges, it analyses the degradation characteristics of bridge materials at the meso-scale level, investigates the damage mechanisms and failure process of the bridge components, and further examines the deterioration laws of the mechanical performance of the in-service concrete bridges at macro-scale level. Finally, based on the analysis and review of the existing investigations, it proposes the current issues in the performance deterioration and preventive maintenance of the in-service concrete bridges, provides new frameworks for future research, and offers the scientific basis for the smart operation and maintenance management throughout the whole life cycle of bridges.

Abstract:【Objective】The vibration of track structure has always been a problem to be studied and solved in related fields. The traditional vibration isolation device is limited by its own weight and the safety of train operation, so it is difficult to realize the broadband control of the bending wave of the track structure.【Method】By introducing the amplitude amplification mechanism, a lever-type track integrated vibration isolation device is designed. Taking the CRTSⅢ slab ballastless track structure as the research object, the energy functional variational method and artificial spring technology are used to establish the periodic track structure fluctuation analysis model and vibration response analysis model with and artificial spring technology. The control ability of track comprehensive vibration isolation device to bending wave is studied,and the relationship between the working ability of track comprehensive vibration isolation device and amplitude amplification coefficient is analyzed.【Result】The results show that the amplitude amplification mechanism can effectively increase the inertial mass of the vibration isolation device, enhance the damping characteristics and stiffness characteristics of the vibration isolation device, and then significantly improve its working ability.【Conclusion】The ultra-wideband bending wave control design goal of the track integrated vibration isolation device low frequency vibration isolation and high frequency vibration absorption is realized.

Abstract:【Objective】The aim of this study is to uncover the bonding mechanism between ribbed steel bars and high-strength cementitious soil. Thirty-three cubic pull-out specimens with dimensions of 150 mm×150 mm×150 mm were produced using an existing cementitious soil solidifier ratio.【Method】Through direct pull-out tests, the influence of anchorage length, cementitious soil cover thickness, and steel bar diameter on the bonding performance between steel bars and cementitious soil was analyzed.【Result】The experiments indicate that the bonding strength at the interface between steel bars and cementitious soil decreases with the increase of anchorage length. The optimal cover thickness for steel bars and cementitious soil is between 2 to 3 times the diameter of the steel bar.【Conclusion】As the diameter of the steel bar increases, the impact of the diameter growth on the bonding strength decreases, especially when the diameter exceeds 10 mm.

Abstract:【Objective】Study on the optimization of foam agent and its solution and the optimal proportion. 【Method】Through systematic experimental research on the research methods of surface tension,foaming ratio, half-life and stability of foam produced by several typical foam agents, the performance index and concentration value of foam agent for optimization were proposed. On this basis, with the C40 cement soil mix ratio as a reference, the prepared foam and C40 cement slurry are mixed according to different injection volume ratios, their dry and wet weight are measured, and the proportioning scheme of lightweight foam concrete under different design weight conditions is determined. Further, unconfined compressive strength tests were conducted to determine the compressive strength of lightweight foam concrete test blocks under different gravity conditions,and electron microscope scanning tests were conducted to understand their microstructure.【Result】The results showed that the optimal concentration of different types of foam agents was about 3%, the foaming ratio was 25, the surface tension was 32 mN/m, and the half-life was 15 minutes; The density and strength of lightweight foam concrete decrease significantly with the increase of foam injection rate,and the corresponding bubble group content and pore size dispersion increase significantly.【Conclusion】Dry density of lightweight foam concrete and the injection rate are in an exponential relationship of attenuation type, and the unconfined uniaxial compressive strength and the dry density of lightweight foam concrete are approximately in an exponential relationship of non gentle increase type.

Abstract:【Objective】To better evaluate the prestress loss of in-service prestressed concrete bridge structures, 【Method】this article takes the 32 m prestressed concrete box girder, which is widely used in domestic highspeed railways, as the research object. 26 test model beams using C50 concrete were produced by converting the box girder into a T-shaped section at a scale of 1:16. The strain and elongation of the prestressed steel strand in the experimental beam were continuously and continuously monitored to determine the actual value of prestress loss, which was then compared and analyzed with the values calculated by commonly used prestress loss calculation specifications at home and abroad.【Result】The findings demonstrate that prestress loss mainly occurs in the early stage, which is instantaneous loss, accounting for about 70% of the total loss. 84.6% of the anchoring losses of the experimental beam account for over 70% of the total instantaneous losses, with a maximum of 80.57%. The long-term loss of the experimental beam fluctuates dramatically in the first 10 days after anchoring and gradually stabilizes in the later stage. Comparing the calculation results of the five specifications with the measured values in the experiment, the data shows that the measured data is most consistent with the calculation results of the "Code for Design of Railway Bridges and Culverts" (TB 10002—2017).【Conclusion】The research results can provide reference for the calculation of prestress loss of prestressed beams in practical engineering.

Abstract:【Objective】Aiming at the problem of poor real-time performance and low precision of traditional pavement crack detection.【Method】This paper uses the advantages of deep learning network in target detection, and proposes an improved YOLOv5 algorithm, which is called YOLOv5s-attention in this paper, to realize the automatic detection and recognition of pavement cracks. Firstly, the collected crack images are manually labeled with LabelImg annotation software, and then the network model parameters were obtained by improving the YOLOv5 network training. Finally, the model is used to verify and predict the cracks. In addition, F₁ and mAP are used to compare the performance of the original YOLOv5s and YOLOv5s-attention models in detecting and identifying pavement cracks.【Result】The comparison between YOLOv5s and YOLOv5s-attention showed that the precision of YOLOv5s attention increased by 1.0%, F₁ increased by 0.9%, and mAP increased by 1.8%.【Conclusion】It can be seen that the network has certain practical significance in realizing the automatic recognition of road cracks.

Abstract:【Objective】In order to study the longitudinal force and deformation law of CWR of ballastless track on the continuous rigid bridge of the metro,and to provide theoretical guidance for the design improvement, operation and maintenance.【Method】Based on the principle of beam-plate-rail interaction, a spatial fine coupling model of CWR of the integral track bed type ballastless track on the continuous rigid bridge of the metro was established,and under stretching, bending,braking and broken rail conditions, the displacementtrack and longitudinal force of track structure and bridge were calculated, and the static characteristics of the track structure were compared and analyzed. This paper provides a reference for the design of CWR track structure on continuous rigid bridge of metro.【Result】The results show that when the midpoint of the double-line train load coincides with the end of the middle beam, the vertical load of the train is the most unfavorable working condition, and the force of the rail and the displacement of the rail and bridge are the largest, and the values are 70.3 kN, 0.6 mm and 0.8 mm, respectively. When the tail of the double-line brake load train is located at the end of the beams on both sides, the most unfavorable working condition of the train braking load, at this time,the longitudinal force of the rail and the longitudinal displacement of the rail and the bridge are the largest, and the values are 107.8 kN, 1.6 mm and 1.7 mm, respectively.【Conclusion】Under expansion force, each end bridge joint is a weak part, and attention should be paid to the structure at the end bridge joint of the beam in the usual maintenance to prevent rail breakage due to excessive expansion force; When the rail is broken under cooling conditions, the longitudinal force and longitudinal displacement of the broken rail are abruptly changed at the fracture, which seriously affects the safety of the line.

Abstract:【Purpose】In order to optimize the emergency response and address the inefficiencies observed in traditional dispatch models, this study tries to develop a scheduling method, which considers a range of emergency dispatch modes.【Method】Considering the characteristics of emergency parking lot dispatching capacity, vehicle transportation capacity, and vehicle rescue time, a multi-objective combination scheduling optimization model is constructed with the goal of minimizing the evacuation cost of emergency public transportation vehicles and minimizing the average passenger delay. Based on the characteristics of the model, a fast non dominated sorting genetic algorithm (NSGA-Ⅱ) was proposed to solve the problem. In order to improve the diversity of the population and the performance of the algorithm, corresponding improvements were made to the algorithm. The Pareto distribution optimization solution set was obtained, and the optimal compromise solution was selected from it using a membership function. Finally, the Nanchang Rail Transit Line 1 was used as an example to separately evaluate the emergency bus combination dispatch plan and the single scheduling scheme are solved separately.【Result】Results show that the proposed combination dispatch plan reduced passenger delay time by 20.48% and transportation costs by 16.96% compared to traditional single dispatch plans. Additionally, the improved NSGA-Ⅱ algorithm further reduced passenger delay time and transportation costs by 6.72% and 3.59%, respectively.【Conclusion】Sensitivity analysis shows that, with clear demands of stranded passengers, fleet size negatively correlated with the average delay time of stranded passengers and positively correlated with emergency bus transportation costs.

Abstract:【Purpose】In order to solve the problem of image classification models lacking open set generalization due to traditional closed set training methods when facing open set recognition problems, we propose a separate independent classification network structure.【Method】Each category contains an independent linear feature layer. The neural nodes designed in the feature layer can capture the category features more accurately under limited data samples. At the same time, a class of negative samples without labeling is introduced in the model training, so that the model not only relies on the feature difference of the known categories when constructing the decision boundary, but also increases the open set generalization of the model decision boundary without adding additional labeled samples.【Result】The results show that both the ICOR model structure and the open-set adaptive training strategy can effectively improve the OSR performance of traditional models; with the increase of openness, it can demonstrate better robustness; can more effectively reduce the OSR risk of the model. 【Conclusion】The proposed independent classification network combined with open-set adaptive training algorithm has better open-set recognition performance than existing open-set recognition algorithms.

Abstract:【Objective】Visible-infrared person re-identification is a very challenging image retrieval problem due to the huge modal difference between visible and infrared images.【Method】In order to further reduce the difference between the two modalities and focus on pedestrian information, a network structure based on dual attention mechanism is proposed for visible-infrared person re-identification. On the one hand, through the dual attention mechanism to mine personal spatial information of different scales and enhance the channel interaction ability of local features. On the other hand, through learning multi-granular feature information through using global and local branches, different granular information can complement with each other to form a more discriminating feature.【Result】Experimental results on two public datasets show that the proposed method has a significant improvement compared with the baseline, and shows ideal performance on both the RegDB dataset and the SYSU-MM01 dataset.【Conclusion】The proposed method can provide an effective reference for solving the problem of modal difference of visible-infrared person re-identification in the future.

Abstract:【Objective】In terms of the rail material, residual stress, temperature stress and other factors, work conditions are respectively designed to explore the influences of rail bottom crack expansion.【Method】Based on the theory of fracture mechanics, combined with rail bottom measurement, the model of rail bottom crack expansion has been established and indicators such as critical crack size, average crack extension rate as well as remaining life has been quantified.【Result】It is found that there exists positive correlation between the fracture toughness of rail material and the remaining life. The remaining life of U95Cr H is less than U78CrV H, which is less than U75V H. Taking U78CrV H, used in the line under test, as an example, when the residual stress grows from 0 to 300 MPa, the critical crack size grows by about 2.5% and the remaining life decreases by about 6%; and when the residual stress is 200 MPa, with the temperature stress from 0 to 200 MPa, the critical crack size does not change much and is within 1%.【Conclusion】The research results of the article can provide reference for the research and maintenance of rail bottom crack propagation.

Abstract:【Objective】In order to investigate the lubricity of methanol and isopropanol under the same load and the different rotational speed, and the effect of rotational speed on the lubricity is mainly emphasize investigated. 【Method】The tribological properties of methanol and isopropanol under 98 N, 400, 500 r/min and 600 r/min are conducted using four-ball wear machine.【Result】The experimental results show that in terms of lubrication system of methanol, the run-in stage is shortened with increasing rotational speed, and the smallest wear scar diameter is obtained at 500 r/min. In terms of the lubrication system of isopropanol, friction coefficient is kept the constant with increasing the rotational speed, but the wear scar diameter initially decreases and then increases with increasing rotational speed, and the smallest one is obtained at 500 r/min.【Conclusion】The low friction and wear of the lubrication system of methanol is attributed to the micro-bearing consisting of tungsten oxide (WO₂ and WO₃), methanol, friction-induced amorphous carbon and tribo-pairs. And the excellent tribological performance of the tribosystem of isopropanol is assigned to the effect of amorphous carbon with lubricity that induced by tribochemistry. Combination of optical microscope, Raman spectra, transition electron microscope, the lubri-cation mechanism of methanol and isopropanol is well investigated. The research results can provide references for the application of alcohols in the field of precision equipment.

Abstract:【Objective】In order to solve the problems of insufficient feature extraction and weak ability of multitarget defect detection of YOLOX algorithm in steel surface defect detection, a multi-dimensional feature fusion strip material surface defect detection algorithm based on improved loss function is proposed.【Method】First of all, apply SPP_SF to the Backbone part to retain multi-scale feature information and improve classification accuracy. Secondly, the multi-dimensional feature fusion module MDFFM is added in the Neck part to integrate the channel, space and position information into the feature vector to strengthen the feature ex-traction ability of the algorithm. Finally, the introduction of Varifocal Loss and α-CIoU is weighted with positive and negative samples to improve the regression accuracy of the prediction box.【Result】The experimental results show that YOLOX-αSMV in NEU-DET data set mAP@0.5:0.95 reaches 47.54%, which is 3.43% higher than YOLOX algorithm. 【Conclusion】The algorithm significantly improves the recognition and localization of fuzzy defects and small target defects while keeping the detection speed basically unchanged.

Abstract:The low-carbon development of cities is an important lever in China's ecological civilization construction, and the“strong provincial capital”strategy has had a significant impact on the coordinated development between regions, which puts forward new requirements for the low-carbon economic development and industrial selection of cities in the Yangtze River Economic Belt under the“strong provincial capital”strategy.【Objective】The study describe the low-carbon economic effects of the industries in the prefecture level cities of the Yangtze River Economic Belt, and discusses the problem of industry selection.【Method】The study uses the random forest model.【Result】The carbon emission reduction potential of urban industries in the Yangtze River Economic Belt is significant, with the construction industry being the largest. Under the strategy of“strengthening provincial capitals”, Shanghai, Wuhan, Chongqing, and Chengdu have relatively full development of low-carbon industries, while small core provincial capitals such as Nanchang, Guiyang, Kunming, and Changsha have great potential for emission reduction in manufacturing and some social service industries.【Conclusion】Provincial capital cities should focus on developing social service industries, while non provincial capital cities should select industries with their own characteristics for key development based on their own resource endowments.