Abstract:For improving the rail transit passenger flow prediction models under rain and snow weather conditions, the passenger flow data of Harbin Metro Line 1 from December 2017 to January 2019 was studied, and the indicators of passenger flow benchmark and passenger flow deviation rate were introduced to quantify the passenger flow of rail transit. The fluctuation rule of rail transit passenger flow under rain and snow weather conditions was analyzed, and a WI-LSTM prediction model was proposed based on the temporal and spatial fluctuation of rail transit passenger flow in rain and snow weather. The mean absolute error (MAE), root mean square error (RMSE), and mean relative error (MRE) were used as the evaluation indexes of the prediction model. The proposed model was compared with SARIMA prediction model, support vector machine (SVR) prediction model, and the LSTM prediction model without considering rain and snow weather. Results show that the WI-LSTM model considering rain and snow weather could make full use of the fluctuation rule of rail transit passenger flow in rain and snow weather, and achieved higher accuracy and reliability than the other three prediction models. The proposed WI-LSTM model further improves the accuracy of rail transit passenger flow forecast in rain and snow weather, and can provide data support for the operation and management of rail transit enterprises.

Abstract:To investigate the main factors affecting the anti-frost properties of asphalt mortar and provide classification and selection principle for limestone powder, we carried out freezing-thawing cycle tests on asphalt mortar with different types of mineral powder. The chemical composition, microscopic morphology, microscopic mechanical property, and rheological property were detected during the freezing-thawing cycles, and random forest analysis was conducted on the test results. Results showed that the addition of mineral powder improved the anti-aging properties of asphalt mortar during freezing and thawing. After freezing-thawing cycles, the decrease in mortar roughness and the increase in surface modulus showed a downward-parabolic trend with the content of CaCO₃ (mass fraction), while the adhesion decreased linearly with the content of CaCO₃. The CaCO₃ content of mineral powder should not be less than 85%, so as to maintain the stability of asphalt mortar properties after freezing-thawing cycles. Asphalt pavement moisture damage was more likely to occur in seasonal frozen area than in non-seasonal frozen area. Compared with non-seasonal frozen area, the CaCO₃ content of mineral powder in seasonal frozen area should be increased by 10%. Random forest analysis showed that the ranking of influence factors of physical and chemical indexes of mineral powder on the properties of mortar were specific surface area (SSA) > CaCO₃ content (CC) > fineness index (X₉₀) > index of plasticity (IP). Specific surface area affected the reaction rate of asphalt and mineral powder, while CaCO₃ content affected the adequacy of the reaction. The technical requirements of limestone rocks and the comprehensive classification technical standards of mineral powder were proposed, which can guide the classification, selection, and production of mineral powder for road usage.

Abstract:For the orthotropic steel-ultra high performance concrete (UHPC) composite bridge deck, the early shrinkage of UHPC is relatively large. Under the constraint of the interface of the composite deck, high-order internal forces can be generated, and there is a risk of cracking, thus endangering the safety and durability of the structure. On the basis of the actual engineering background, the shrinkage effect of the composite bridge deck with wet joints was monitored for 90 d under normal temperature curing in natural environment. The development and distribution of UHPC shrinkage of composite bridge deck and the induced secondary internal force were investigated, and the influence of age difference on the development of the shrinkage effect of wet joint area was explored. The finite element model of plate and shell was established, and the shrinkage effect before and after the wet joint pouring of composite bridge deck was simulated by linear superposition of multiple models. Test and finite element analysis results showed that under hot and humid curing environment, the shrinkage development of UHPC experienced four stages: early expansion, rapid shrinkage after initial setting and hardening, slow shrinkage, and stability. The initial setting and hardening of UHPC occurred about 6 h after pouring. Taking the strain at this moment as the reference, the measured shrinkage of UHPC for the first 72 h was about 700×10^-6, and the maximum compressive strain of the steel deck flange measured during this period was about 78×10^-6. UHPC shrinkage was larger in the area near the edge of the bridge deck and smaller in the area near the center of the deck. The shrinkage measured at the wet joint after initial setting and hardening was smaller than that in the surrounding area. The wet joint was well connected with the surrounding area, and the UHPC tensile stress caused by shrinkage tended to increase near the wet joint. The research results can accumulate monitoring data and foundation for the study of shrinkage of composite bridge deck with wet joints.

Abstract:For the improvement of emergency management, the degree of material demand for different disaster-stricken sites was quantified, and an optimal route planning method for vehicles was proposed considering the urgency of demand. The K-means clustering algorithm was utilized to determine the selection of emergency material distribution centers and the division of disaster-affected points. With the shortest total time in the emergency rescue process, the minimum total cost of the rescue, and the maximum urgency ranking index of the disaster-affected points as the goal, a multi-objective emergency vehicle routing optimization model was established, and an improved cuckoo-ant colony hybrid algorithm was designed to solve it. Taking the Wenchuan earthquake as the background, the effectiveness of the proposed model was verified. Results show that compared with the vehicle routing scheme without considering demand urgency, the routing optimization scheme considering demand urgency increased the urgency ranking index by 11.2% on the premise that the total transportation time and the total cost of rescue process increased by 1.92% and 3.43%. The vehicle routing optimization model considering the urgency of demand not only ensures the rescue efficiency of sudden disasters, but also considers the material demand degree of different disasters-affected points, and improves the fairness of emergency material transportation.

Abstract:For the coordinated development of urban rail transit network and urban spatial structure, a spatial simultaneous equation was utilized based on multi-source spatiotemporal data to analyze the spatial interaction between jobs-housing spatial structure and rail transit network. The jobs-housing self-contained index was employed to measure the urban jobs-housing balance. On the basis of the actual road network, the Gaussian-based two-step floating catchment area (2SFCA) method was used to calculate the accessibility of rail transit stations. A spatial simultaneous equation was utilized to reveal the spatial interaction effect between jobs-housing balance and rail transit accessibility. The spatial autocorrelation analysis was introduced to explore the coupling between the urban jobs-housing space and the rail transit network in Xi′an. Results show that the Gaussian 2SFCA method based on the actual road network can evaluate the accessibility of rail transit more reasonably. There is mutual feedback effect mechanism between regional jobs-housing balance and rail transit accessibility: both of them have positive spatial spillover effect, and there is a positive interaction spatial spillover effect between them. From the perspective of local coupling effect, the planning and construction of rail transit in the north and southwest of the main urban area of Xi′an should be strengthened. The urban spatial structure can be optimized through the guidance of urban rail transit on urban development. The research results can reveal the interaction between urban rail transit network and jobs-housing space and play a reasonable role in guiding urban rail transit to optimize urban spatial layout.

Abstract:To verify the feasibility of 915 MHz microwave frequency for regenerative heating of asphalt pavement materials, on the basis of analyzing the microwave heating mechanism, the horn antenna parameters were designed and optimized, and the heating effect of single antenna and array antenna on asphalt mixture under two microwave frequencies of 915 MHz and 2 450 MHz was compared by using CST simulation software. The influencing factors such as antenna spacing, heating height, and mixture thickness on the heating effect were simulated. Results show that the asphalt mixture heated by 915 MHz microwave frequency had better uniformity and a smaller temperature gradient in the depth direction. The variation of the antenna spacing, heating height, and mixture thickness caused changes in the microwave interference phenomenon in the heating box, which in turn affected the heating effect. Under the conditions of mixture thickness 250 mm, antenna spacing 70 mm×70 mm, and heating height 70 mm, the heating effect was the best, the average temperature of the mixture was the highest, and the discrete coefficient was the lowest, with good temperature uniformity and less asphalt aging phenomenon. For large-scale microwave regenerative heating equipment, due to the requirements for large heating thickness and high output, 915 MHz is recommended.

Abstract:To study whether the connection of precast piers can form a reliable force transmission mechanism and its seismic performance, based on a set of quasi-static tests of precast piers, we established finite element models of the test piers by ABAQUS and verified the effectiveness through test results. Then, the seismic dynamic responses of cast-in-place pier, precast pier with grouted corrugated duct connection, and precast pier with tenon-grouted corrugated duct connection were analyzed. Finally, the influence of axial compression ratio and reinforcement ratio on the seismic dynamic response of the precast pier with tenon structure was further studied. Results show that the dynamic responses of precast pier and cast-in-place pier were basically the same under the same structural form and seismic load. The displacement response, residual displacement, and plastic damage of precast pier with tenon were smaller than those with plane joint, and the seismic performance of precast pier with tenon was improved. Through parameter analysis, it was found that with the increase in the axial compression ratio, the displacement response and plastic damage of the pier were larger, and the shear response and seismic energy consumption were greater. With increasing longitudinal reinforcement ratio, the displacement response and plastic damage of the pier decreased, and the shear response increased, while the influence on the seismic energy dissipation was not significant in the range of 1% to 2%.

Abstract:To provide a theoretical basis for quantifying the moisture damage of asphalt pavement from the perspective of water vapor and explore the influence factors of water vapor diffusion in semi-rigid bases, the two main influencing factors (material thickness and temperature conditions) were determined through theoretical derivation, and the test device and test plan were designed to explore the influence of material thickness and temperature conditions on water vapor diffusion in semi-rigid bases. Results show that the water vapor diffusion in the semi-rigid base layer had no relation with the relative humidity difference between its two sides, but was related to temperature conditions and material thickness. The water vapor diffusion flux gradually decreased as the material thickness increased, and the decreasing trend gradually slowed down; while the water vapor diffusion coefficient increased as the material thickness increased, and the increasing trend gradually slowed down, which indicates that the increase in material thickness hinders the diffusion of water vapor in the semi-rigid base layer to a certain extent. The water vapor diffusion flux increased with the increase in temperature, and the increasing trend gradually intensified; while the water vapor diffusion coefficient increased with the increase in temperature, and the increasing trend gradually intensified, which indicates that the increase in temperature can provide more energy for the diffusion of water vapor and aggravate the diffusion of water vapor in the semi-rigid base layer.

Abstract:To study the influence of expansion joint parameters on vehicle-induced dynamic response of long-span concrete-filled steel tube (CFST) arch bridge, this paper proposes a vehicle-bridge coupling dynamic response analysis method (vehicle-gap-bridge coupling dynamic response analysis method) considering the influence of expansion joint parameters. Taking a long-span half-through CFST arch bridge as the research object, the influence of expansion joint height difference, support stiffness, and joint width on the vehicle-gap-bridge coupling dynamic response was investigated. Results show that under the design parameters of expansion joint, the vertical impact of vehicle on expansion joint first decreased and then increased with the increase in the vehicle speed, and the vehicle-induced impact on the expansion joint was more significant than that on the main beam. With the increase in the vehicle speed, the vehicle-induced impact coefficient of the main beam showed an increasing trend. Considering the influence of expansion joint parameters, the vertical impact of vehicle on the main beam was related to the spatial position, and the impact coefficient of the main beam measurement point close to the expansion joint position was greater. Under variable expansion joint parameters, the rise of the middle cross beam led to the increase in the impact of the vehicle on the expansion joint, and the rise or fall of the middle cross beam could both cause the increase in the impact of the vehicle on the beam end, resulting in the increase in the bearing reaction. When the support stiffness of the expansion joint decreased or the width of the joint increased, the impact of the vehicle on the middle cross beam of the expansion joint increased. The expansion joint parameters had little effect on the displacement response of the 1/4 cross-section and 1/2 cross-section of the main beam.

Abstract:For the efficient selection of a feasible cooling method before the design of external cooling system for a converter valve, the local climate environment and converter station equipment conditions were analyzed, and a residual network model based on stacking heterogeneous (SH-ResNet) was built to classify cooling methods. The model integrated supervised classifiers and unsupervised clustering algorithms, and ResNet was regarded as a meta-classifier to deeply explore the potential connections of the output results. The climate environment, converter valve cooling system requirements, equipment layout, and the corresponding cooling methods adopted in different regions in recent years were investigated, and a total of 209 samples were used to train and evaluate the proposed model. Results show that the classification accuracy rate of SH-ResNet reached 0.97, which was an average increase of 11.46% compared with the base classifiers. It indicates that the model maintains strong generalization ability and improves the classification accuracy in spite of small training sets. Finally, the interactive window of the cooling method recommendation system based on the proposed model was designed. It not only gives the recommended proportion for each cooling method, but also visualizes the relationship between the characteristic parameters and the cooling method, which provides an optimal method for the design of external cooling system of converter valves.

Abstract:For the carbonate soil in the western part of Jilin province, considering different methods of modifying soil using lime and lime + fly ash, the engineering and strength characteristics of carbonate soil improved by lime and lime + fly ash were studied via limit moisture content test, compaction test, and triaxial shear test. Combined with the analysis of consolidation compression test, the deformation characteristics of the improved saline soil were discussed. Results show that the lime and lime + fly ash modifiers could effectively improve the plasticity and compaction characteristics of the carbonate soil. With the addition of lime and lime + fly ash modifiers to the carbonate soil, the shear strength of the improved soil was increased. When the dosage reached 9%, the strength of lime-modified soil decreased, while the strength of the soil modified by lime + fly ash varied with different salt contents, resulting in different improvement effects. The improved saline soil transformed from medium compressive soil into low compressive soil. With the increase in the maintenance age, the compressive deformation of the soil decreased. The compressibility of the saline soil could reach the best by adding a reasonable amount of modifier.

Abstract:For constructing the urban public transportation network that is more in line with the actual transfer willingness of residents, on the basis of the space-M method of complex network theory, the connecting edge rule of two-layer network with carrying capacity as edge weights was proposed considering the travel characteristics of urban residents in alpine area. The weighted two-layer network model of subway-bus network was constructed, and the statistical characteristics and carrying capacity calculation method were given. According to the survey of transfer willingness of residents, the transfer willingness of subway-bus stations varied obviously in different seasons. Then, taking the subway-bus network in Harbin as an example, the overall carrying capacity, edge carrying capacity, and node carrying capacity in winter and other seasons were compared, and the robustness of the network was analyzed. Results show that the overall carrying capacity of Harbin subway-bus network in winter was 7 960 594 person/h, which was lower than that in other seasons (8 338 903 person/h). Therefore, for alpine cities, more favorable management and control measures for subway and conventional public transportation should be implemented in winter to improve network carrying capacity.

Abstract:To improve the safety and reliability of lithium-ion battery operation and maintain the stable operation of the system, we proposed a prediction method for remaining useful life (RUL) of lithium-ion batteries based on adaptive hybrid model and improved particle filter (PF) algorithm. An adaptive hybrid model was established by combining empirical model and neural network model to describe the degradation trend of battery capacity, and beetle antennae search (BAS) algorithm was used to optimize the PF resampling step to solve the problem of loss of particle diversity, so as to improve the estimation accuracy and achieve accurate RUL prediction. Two groups of different types of lithium-ion batteries published by NASA and CALCE were selected as the research objects to verify the validity of the model and the accuracy of RUL prediction via comparing PF and improved PF algorithms. Experimental results show that the adaptive hybrid model was more expressive in terms of battery capacity change, which can reflect the variation of the internal parameters as well as the external environment of the battery. Compared with the traditional PF algorithm, the BAS-based improved PF (BAS-PF) method had higher estimation accuracy and more accurate RUL prediction results with the prediction errors of 5.88%, 3.92%, 1.96%, and 3.75%, 1.25%, 0%, respectively, for the two test batteries from different prediction points. The adaptive hybrid model can describe the characteristics of battery capacity more effectively, and the BAS-PF algorithm based on adaptive hybrid model has better prediction ability and greater reliability for battery RUL, which is helpful to improve the prediction accuracy and performance for RUL.

Abstract:To clarify the safety performance of downward movable scaffolding systems (MSSs) in strong wind environment, this paper takes a downward mobile scaffolding system with span of 50 m (MSS50) in the southeast coastal area as the research object to systematically investigate its flutter, vortex, and buffeting performance by aero-elastic model wind tunnel test and numerical calculation. Results show that vertical displacement and torsion angle were critical factors of MSS in fixing and moving conditions respectively. In the fixing condition, MSS50 could meet the operation requirements of 8-level strong wind (20.7 m/s) and resist 14-level wind (46.1 m/s). In the moving condition, the main structure could meet the operation requirements of 8-level strong wind in the case of proper measures. The multi-modal coupling frequency domain buffeting calculation method and the equivalent static gust wind load method in Wind-resistant Design Specification for Highway Bridges could be used to calculate the buffeting response of MSS with acceptable accuracy. The multi-modal coupling frequency domain buffeting calculation method has higher accuracy than the equivalent static gust wind load method and is recommended to calculate the buffeting response of MSS.

Abstract:For improving the existing thermal stress calculation methods of asphalt binders, the bending beam rheological (BBR) test was performed to obtain the creep compliance of asphalt material, and the strain-stress relationship of the linear viscoelastic Burgers model was introduced to obtain the rheological parameters at different temperatures. The analytical solution of the constitutive equation of state of the Burgers model was used to calculate the numerical solution of the thermal stress under the asphalt layer (incremental method), and the calculation results were compared with the results of the traditional Hopkins and Hamming′s algorithm. Results show that the two methods were basically consistent, but at a lower temperature (around -30 ℃) the results of the Hopkins and Hamming′s algorithm were smaller than those of the incremental method, underestimating the effect of thermally reversible aging. The hardening effect of low-temperature curing on asphalt was related to the rheological properties of asphalt. The more complex the rheological properties of asphalt were, the more obvious the hardening effect of low-temperature curing was. When under low temperature or long-term loading, the rigidity master curve of the thermo-rheological complicated asphalt deviated from the timek-temperature superposition principle.

Abstract:Considering the problem that the load disturbance and track “step” phenomenon may lead to instability of maglev trains, the active disturbance rejection generalized predictive control (LADRC-GPC) theory was introduced into the levitation system of maglev train, and a new suspension controller was designed. The controller adopted a layered control strategy, and the extended state observer (ESO) was used to dynamically compensate the system in the inner layer. The controlled autoregressive moving average model (CARMA) of the controlled object was obtained to reduce the dependence on the mathematical model of the controlled object. The inner layer was taken as the controlled object by the outer layer, and the generalized predictive control (GPC) was used to dynamically optimize the control system, which improved the tracking performance of the controller. By comparing with PID control algorithm and linear active disturbance rejection control (LADRC) algorithm through simulation and experiment, results show that the LADRC-GPC algorithm had better tracking performance and robustness, and could maintain small error under large load disturbance.