Abstract:In order to evaluate the application of the post-combined prestressing method in continuous composite bridge， and compare the post-combined prestressing method with the conventional pre-combined method， the formulas of section stress at the intermediate support from a post-combined and pre-combined composite bridge were derived based on the transformed section method. The field test was also conducted on the first large span post-combined continuous composite bridge constructed in China. The section stress at the intermediate support was measured during each construction stage. The test result shows that the post-combined method will not introduce compressive stress in the steel beam， which improves the efficiency of the prestressing the concrete deck. The concrete stress generated by the post-combined method is 1.3 times that of the concrete stress generated by the conventional prestressing method. The calculation that the post-combined method can achieve the full prestressing state of the concrete deck in the continuous composite bridge with a span less than 70 m， and the concrete deck without cracking can be realized in the continuous composite bridge with a span less than 110 m.

Abstract:In order to study the mechanical behavior of steel-concrete composite beams with different shear connection degree， finite element models of composite beams are established. In addition， the validity and correctness of models are verified by four beam tests. Moreover， factors such as the number， diameter， length and material strength of the studs are selected to conduct the parametric study， by using the orthogonal test method. Furthermore， the influence of shear connection degree is discussed and the fitting formulas of bending capacity and end slip of composite beams are obtained. The results show that the number and diameter of studs have the most significant effect on the interface slip of composite beams. In addition， the bending capacity and beam end slip of composite beams with different connection degrees can be accurately predicted using fitting formulas. Moreover， in bridge engineering， as the studs are usually distributed according to structural requirements， the limit value of interface slip is not the controlling factor when designing composite beams.

Abstract:To study the mechanical properties of the rubber-sleeved stud connector and its influence on the steel-concrete composite girder， 5 groups of 15 push-out test specimens are designed and fabricated. The mechanical behavior of the rubber-sleeved stud connector is revealed by using the static loading test while the influence of the rubber-sleeved stud connector on the steel-concrete composite girder is analyzed by using the FEM（finiti element method） models. The test and finite element analysis results show that the rubber-sleeved stud connector helps to reduce the shear stiffness of the push-out test specimens without decreasing the carrying capacity. Meanwhile， the rubber sleeve has little impact on the mid-span deflection and the stress in the steel girder but magnificently decreases the stress in the concrete slab at the mid-support. For composite bridges using shear connectors with a diameter of 22 mm and 19mm， the tensile stress in concrete slab decreases by 26 % and 13 % respectively. As for the problem of sudden stress change， a transition area of 2m at the intersection of the positive moment region and the negative moment region can reduce the stress mutation by 30 %， which effectively improve the adverse condition in the stiffness changing region.

Abstract:In order to investigate the effects of short stud arrangement on flexural behavior of steel-ultra-high performance concrete （UHPC） composite bridge decks， flexural tests of two full-scale segmental bridge deck specimens with a stud spacing of 200 and 300 mm respectively were performed， and a finite element parametric analysis based on the UHPC plastic damage model was conducted. The test results show that， as the stud spacing of partially-composited bridge decks increases from 200 mm to 300 mm， when the UHPC cracking reaches up to 0.05 mm in width， the corresponding load increases by 12.5 %. The main contributor is the weakening of the steel-UHPC combination effect. The average tensile strain of the UHPC is 1 878×10^-6 as the cracking reaches 0.10 mm in width， accounting for about 59 % of the material ultimate tensile strain. The parametric analysis shows that as the stud spacing increases from 100 mm to 400 mm， the elastic bending stiffness decreases by 14.1 %， while the cracking load increases by 84.2 %. The increase of the short stud spacing makes the partially-composited bridge deck tend to be more mechanical-economical， but attention should be paid to the fatigue damage of the stud because of the too large stud spacing.

Abstract:In order to validate the fatigue behavior enhancement as derived from ultra-high performance concrete（UHPC） reinforcement， typical welded details of rib-to-deck-to-floor beam （RDF） connections in orthotropic steel decks were tested by employing single- and double-wheel loading conditions. Static loading was first conducted to investigate the local stress distributions at critical areas. High-cycle constant amplitude cyclic tests were then conducted to obtain the fatigue behaviors including crack initiation and propagation， fatigue failure mode， rigidity degradation， and fatigue life of RDF connections. The results show that， by introducing the UHPC reinforcement layer， the hot spot stresses at weld toes of specimens weresignificantly reduced by up to 58 %. When compared to the specimens without the UHPC layer， the numbers of fatigue cracks of steel-UHPC composite connections were found to be reduced， and the fatigue crack growth rates and the rigidity degradation speeds were also observed to be significantly depressed during the whole process of test. The S-N curve of category FAT 90 and FAT 100 as provided in international institute of welding （IIW） fatigue design recommendations can be used to predict the fatigue lives of the steel bridge decks before and after UHPC paving.

Abstract:In order to predict the nonlinear time series of geotechnical engineering more precisely， a wavelet-optimized LSTM-ARMA model is proposed. First， the monitoring series are decomposed into a trend term and a noise term through wavelet analysis. Then， the trend term is predicted by the long short-term memory network （LSTM）， while the noise term by the autoregressive moving average model （ARMA）. Finally， the sum of the predicted values of both terms is taken as the total predicted results. The performance of the method is validated through the case analysis of an ultra-deep foundation pit which also indicates that the combined model gives a more precise and stable prediction than the LSTM network. Besides， the elastic-plastic finite element method is also used to predict the ground settlement induced by foundation pit excavation， and its results are compared with those of the artificial intelligence method， verifying the rationality of the latter. The analysis shows that the prediction error of the artificial intelligent method will increase significantly when the deformation mechanisms of the previous and the subsequent working conditions change suddenly， but it will decrease gradually with the progress of the subsequent working conditions.

Abstract:Based on a case of a super large underground complex construction adjacent to a historical building in Shanghai， a three-dimensional finite element model considering small strain characteristics of soil was established to examine the deformation characteristics and stress path of soils during excavation. The field measurement data were utilized for the validation of model parameters， and six different construction conditions were calculated and analyzed. The results showed that the effect of only optimizing the excavation sequence on controlling the deformation of the foundation pit was limited and not comprehensive. It was necessary to consider the influence of integral stiffness of underground structure and boundary condition change during the whole construction process. The comparison that the optimal construction scheme was to excavate smaller pits first， followed by the completion of the underground structure and the construction of larger pits， which could reduce the lateral displacement of the retaining structure close to the sensitive building by 30 % compared with the adverse condition. In addition， different excavation sequences， boundary conditions， and drainage conditions made the stress state of soils inside and outside the pit more complex and varied. The soils inside the pit presented diverse stress paths in different unloading conditions， while the soil outside the pit showed a multiple unloading stress path. The application of the servo prestressed steel support could control the deflection of the retaining wall close to the protection object within 0.1% H_e （excavation depth）， and the retaining wall might move towards the outside of the pit under the combined action of steel supports at each level. Moreover， the soil outside the pit would exhibit the stress path of horizontal unloading first and then loading.

Abstract:The effects of initial relative density， fine particle content and consolidation mode on static liquefaction of sand were studied by using consolidated undrained triaxial shear test. For pure Toyoura sand， the stress-strain relationship of medium dense and dense samples shows continuous strain hardening characteristic， and the pore pressure first increases and then decreases to negative values. The continuously strain softening occurs only in the very loose sample （D_r=5 %）. The results indicate that when the content of fine particles is low， the sand is more prone to strain softening. Based on the test results and the calculated second-order work， the stress ratio corresponding to the triggering point of static liquefaction instability of sand is obtained. The stress ratio increases with the increase of initial compactness and decreases with the increase of fine-grained content， indicating that loose specimen with a high fine-grain content is apt to trigger static liquefaction instability.

Abstract:With consideration of the differences of vehicle emissions limits standards and testing driving cycles between China and the United States， a method of MOVES（motor vehicle emissions simulator） localization is proposed， and a case study of Shanghai is made. The result reveals that although the vehicle emission control in China lags behind， it develops rapidly. For example， the emission characteristic years of light-duty vehicles in the United States corresponding to the carbon monoxide emission limit standards of China I to China VIa are 1995， 1999， 2002， 2007， 2010 and 2012. The estimated light duty vehicle emissions factors are compared with the real test results.

Abstract:For the layout of auxiliary stopping areas （ASAs） considering complex scenarios， taking the line with multi-target speed profiles as research objects， aimed at minimizing the number of ASAs and the train tracking interval， a multi-objective optimization model constrained with the safe operation of trains is established. In addition， a fast and elitist non-dominated sorting generic algorithm （NSGA-II） is designed and discussed. Moreover， to make the algorithm has a better performance， a population initialization strategy considering the layout characteristics of ASAs is proposed. The simulation results verify the effectiveness of the model and the algorithm on solving the layout problem of ASAs in complex scenarios. This paper can provide a new idea for solving related problems.

Abstract:To effectively evaluate and predict the fatigue life of the W300-1 fastening clip during service， a finite element model was established， by considering the elastic-plastic mechanical properties and nonlinear contact relations of the clip. The strain characteristics of the clip at different installation loads were analyzed， and the test results were verified based on digital image correlation （DIC） technology. The fatigue life of the clip was calculated by applying the fatigue load in combination with the strain-life curve based on the actual measurement wheel-rail force time-history curve of Beijing-Shanghai High Speed Railway. The influence of installation torque， fatigue cycle load amplitude and the matching relations between them （the stress ratio） on the fatigue life of the clip was analyzed. The results show that the lowest fatigue life is found at the heel of the clip， and plastic deformation occurs no matter in a state of slightly under-tightening installation， normal installation， or over-tightening installation. The fatigue life decreases with the increase of installation torque and fatigue load amplitude， but it is linearly proportional to the stress ratio at the dangerous point of the clip. Therefore， to ensure the actual service life of the clip， especially in high speed or serious corrugation lines， it is recommended that the installation torque of the clip should not exceed 300 N·m.

Abstract:Simulation-based scenario testing methods have drawn significant research interests， and how to find critical testing scenarios among the infinite number of concrete scenarios becomes a critical issue. To solve this problem， this paper proposed a critical scenario generation and automatic testing method for the decision and planning system based on optimization and search algorithms. The method was verified through a hardware-in-the-loop platform， and the efficiencies of different search algorithms were compared. The experiment results show that the number of critical scenarios generated by the Bayesian optimization algorithm and the genetic algorithm is increased by 3 times and 2.5 times， compared with the random search algorithm. Combined with automatic testing， the method can quite improve testing efficiency.

Abstract:Under engine idling condition， the mechanism of rattle between damping spring and secondary side and the rattle between secondary side spline and transmission input shaft when dual mass flywheel matched with dual clutch transmission were studied. The knocking energy was proposed as an index to evaluate the rattle noise. The design of experiments （DOE） method was used to guide the simulation， and the influences of the key parameters of the dual mass flywheel on the impact energy were clarified. The solution of optimize basic friction to restrain rattle were proposed. The effectiveness of DOE simulation test was verified by experiments， and the consistency between the proposed impact energy evaluation method and subjective evaluation results was verified.

Abstract:Due to the importance of the pantograph for high-speed train， the aerodynamic and noise simulation analyses of the pantographs with circular cylinder and twisted cylinder were conducted. Compared with the pantograph with circular cylinder， although the average resistance of the pantograph with twisted cylinder is slightly increased， its average and pulsating lift force is greatly reduced， which is helpful to improve the operation stability and current quality of the pantograph from the viewpoint of aerodynamic. The cluster analysis of the pantograph wake flow field indicates that there are three closed-loop conversion paths in the wake flow field of pantograph with circular cylinder and twisted cylinder. Compared with the circular cylinder， the second conversion path of the twisted cylinder is slightly shorter， but the third conversion path is slightly longer. When the lower arm changes from the circular cylinder to the twisted cylinder， the single vortex transforms to multiple alternating positive and negative vortices in the vertical direction. The pantograph with the twisted cylinder can eliminate the peak noise of the pantograph with the circular cylinder and reduce the total sound pressure level by 1.5 dB， which is beneficial to improve the aerodynamic noise performance of the pantograph.

Abstract:This paper presents a feedforward-feedback control system based on the double neural network. The operation data of the single gimbal control moment gyro（SGCMG） system under different conditions is collected and processed by Kalman filter. A virtual generalized controlled object model covering the information of the control channel and the disturbance channel is constructed based on neural network， and a neural network feedforward compensator is designed. The composite control system of feedforward compensator and original feedback controller is realized， which reduces the constraint that the traditional feedforward-feedback composite control needs to obtain the disturbance channel information accurately， and can overcome the influence of the complex disturbance existing in the SGCMG system on the control performance. The simulation results show that the scheme can improve the steady-state accuracy of the system， reduce the steady-state error and improve the control dynamic performance.

Abstract:Workflow scheduling in multi-cloud environment is a research hotspot and challenge in recent years. The dependencies in workflow are usually represented by the transmission of data， which also determines the execution order of tasks. Existing studies for workflow scheduling usually map each task to a different cloud resource， which is difficult to solve the problems of increasing make-span and cost， and the possible failure risk caused by frequent data communication. In order to reduce the impact of data communication between tasks， this paper proposes a workflow slicing and multi-cloud scheduling solution based on clustering coefficient. Preliminary slicing of workflow is conducted by using a clustering algorithm， and the clustering coefficient is introduced to evaluate and optimize the slicing effect. In the process of finding the optimal scheduling solution， the slicing result is adjusted dynamically according to the actual situation of cloud instances. Experimental results show that the proposed method can effectively reduce the high cost and make-span caused by large amount of data communications in workflow.

Abstract:This paper introduced the geolocation equations and solution procedures of synthetic aperture radar （SAR） imaging geodesy in details， and conducted precise positioning of point targets in SAR images based on the weigh-centroid method. Regarding to the poor geolocation accuracy and solution stability caused by very short spatial baselines with single track SAR images， a height constraint was added to the geolocation model. By adopting multiple high-resolution TerraSAR-X and Sentinel-1 SAR images， the absolute geolocation was implemented to six corner reflectors（CRs） located at Wuhan and Shanghai， respectively. The experiments demonstrate that the absolute geolocation accuracy of CRs at centimeter-level can be achieved by using TerraSAR-X SAR images， and decimeter-level positioning accuracy by using Sentinel-1 SAR images.