Abstract:The structural composition of long-span cable-stayed bridges in mountainous area is complex. As the static behavior of the whole structure under live loads presents obvious nonlinearities, the structural stability problem is prominent. Therefore,based on a steel truss girder cable-stayed bridge with a main span of 930 m under construction in the south mountainous area of Yunnan Province, China, the ultimate load carrying capacity analysis is carried out by using limit point instability theory where both structural geometric and material nonlinearities are considered. It is aimed at investigating the nonlinear behavior and failure mechanism of such a long-span bridge under live loading. Because of the existence of “canyon effect” for the wind in the mountainous area, the bridge is easy to be affected by wind loads during construction. Subsequently, the ultimate load carrying capacity analysis of the bridge at the maximum cantilever construction state is performed under static wind loading. The results have shown that the geometric nonlinearity has less influence on the structural performance than the material nonlinearity does. The ultimate load carrying capacity of the long-span cable-stayed bridge is controlled by the material failure of the cable. With the increase in live load, the elastic-plastic zones develop gradually. The tensile and compressive plastic zones appear successively on the steel truss girder, forming four yield paths. At the maximum cantilever construction stage, the calculated ultimate load capacity is greater than static wind load of Grade 12 wind speed.

Abstract:In order to study the relationship between mixture gradation variation and road performance, the road performance of asphalt mixture was predicted. In this paper, a typical asphalt mixture grading variation model was constructed, and the screening residual characteristic parameters were proposed to characterize the mixture grading variation characteristics. SPSS software was used to analyze the correlation between the structural parameters of the mixture and the road performance, and a prediction method for the road performance of asphalt mixture was established, with the asphalt mixture structural parameters as the medium. Through regression analysis, the relationship equation between the variable gradation screen residual characteristic parameters and the road performance index is established, and the qualification criteria of each road performance index value is determined. The results show that the prediction of Marshall stability, freeze-thaw splitting strength ratio, creep rate and residual stability of asphalt mixture are in good agreement with the actual results. It can be used to predict the partial pavement performance of asphalt mixture with variable gradation, adjust the construction mix quickly without affecting the construction process, and ensure the pavement performance of asphalt mixture.

Abstract:The fatigue mechanism at the connection between longitudinal ribs and diaphragm of orthogonal anisotropic steel bridge panel is complicated and difficult to analyze. In order to address this problem, the area around the curved opening of diaphragm and U-rib and the weld end of diaphragm is taken as the research location, and the stress distribution law in the area is combined with the in-depth analysis of the stress mechanism to find out the fatigue susceptibility point in this area. Taking the fatigue stress of the construction details as the control index, we propose the construction forms to reduce the fatigue stress such as variable thickness transverse spacer, double internal spacer and reverse arc notch at the connection between the transverse spacer and longitudinal ribs, etc. After the finite element calculations, the results show that: the variable thickness transverse spacer and the double internal spacer have an obvious effect on the fatigue at the arc openings and the end of the weld seam, respectively, the reverse arc notch makes the geometrical linearity smoother and reduces the stress concentration caused by geometrical discontinuities. Geometrical discontinuities, which can significantly reduce the fatigue stresses in the above two types of fatigue details.

Abstract:In order to improve the anti-cracking performance of tuff manufactured sand concrete, the mixing ratio of manufactured sand and stone powder content were taken as the main influencing factors, and the quantitative evaluation method of concrete cracking risk based on tubular cracking test was proposed. At the same time, the working performance, mechanical properties, impermeability and sulfate corrosion resistance of tuff manufactured sand concrete were systematically studied. The test results indicated that the workability and strength of all machine-made sand concrete were the best when the content of stone powder is 5%(mass fraction). The sulfate resistance and impermeability gradually were decreased with the increase of stone powder content, and the possibility of dry shrinkage and cracking were greater. For the concrete mixed with natural sand and manufactured sand, the mechanical properties of concrete decreased gradually with the increase of the proportion of natural sand; Under the proportion of 30% natural sand, it has good sulfate resistance and permeability resistance. Although the fully manufactured sand concrete is not as good as the natural sand concrete in terms of workability, it is superior in strength and crack resistance. Using manufactured sand to replace natural sand can get better benefits, but at the same time, the limit of stone powder content should be strictly controlled (the mass fraction not more than 7%). When natural sand and tuff machine-made sand are mixed, the comprehensive performance of concrete is the best under the mixing ratio of 30% natural sand.

Abstract:To address the issue of frequent rear-end collisions on mountainous road sections, the risk of vehicle rear-end collisions on curved slope combination sections is assessed based on traffic conflict technology, and the influencing factors of rear-end collisions are identified. Vehicle trajectory and traffic flow data are collected through aerial photography by UAV (Unmanned aerial vehicle) and radar speed measurement. The traditional time to collision (TTC) calculation method has not fully considered the alignment characteristics of the curved slope combination section. According to the characteristics of road alignment and vehicle operation in each component (circle curve section, gentle curve section and straight curve section) of the curved slope combination road section, the vehicle rear-end collision time TTC is modified, and the classification thresholds of severe, moderate, slight and potential rear-end conflicts are 1.23 s, 2.59 s, 3.50 s and 4.0 s according to the cumulative distribution curve of conflict time. The tree structures for identifying the influence factors of rear-end conflicts on circular curve, gentle curve and straight curve road sections were constructed respectively, and the influence of each factor on the severity of rear-end conflicts was investigated by ordered logistic models. The results indicate that: the increase of traffic volume, the mixing of large vehicles, and the increase of vehicle travel speed and acceleration will promote the occurrence of conflicts as well as the severity of conflicts; There are differences in the effects of traffic flow characteristics indexes on rear-end conflicts in each road section; No significant differences in rear-end conflicts were found between vehicles approaching or exiting the direction of curves, and between inside and outside curves on circle sections; however, such differences existed on gently curved and straight sections. The results of this research help active safety prevention and control of rear-end collisions, as well as real-time forecasting to improve safety of travelling on curved road sections.

Abstract:To investigate the system nonlinear redundancy performance of a multi-girder steel plate composite girder bridge under asymmetric extreme loads, three bending failure modes of the system were identified along the force transmission path of the structure and the rebalancing process of the system. A new performance indicator was derived for quantitatively evaluating the elastic distribution and plastic redistribution of the system, and the redundancy evaluation method of time-varying system was established considering the time-varying variability of load mechanism. The management program of time-varying evolution parameter set of element fibers was written based on MATLAB/OpenSEES, and the influence of material deterioration on the rebalancing and internal force redistribution of the system was studied. The overall elastoplastic process analysis of the structure under asymmetric load was carried out based on the numerical increment algorithm. The accuracy of the numerical model was verified by comparing it with the failure tests at the component-system level, and then a nonlinear redundant numerical simulation method of time-varying system based on fiber macro-element was established. Results showed that material deterioration caused the transformation of the system from multi-girder cooperative bearing mechanism to single beam bearing mechanism, and resulted in varying degrees of degradation of member ductility, system redundancy, and reliability. Fewer beams or fewer transverse connections, while better suited for on-site rapid assembly, were prone to insufficient component safety and system redundancy in the service life. The failure of main beam, middle transverse joint, and end transverse joint had a great impact on the bearing performance of the system, which were key members of steel plate composite beam bridge, whereas the sensitivity of other transverse connections was low, which were non-key components.

Abstract:In order to study the effect of different positions and quantities of tension bands on the stability of geocell retaining wall upder earthquake action, a numerical model of geocellular retaining wall supporting slope was established with the help of FLAC^3D software, and the results of shaking table test were used to verify the numerical model. The calibrated numerical model was used to systematically study the influence of different positions and quantities of tensile strip on the dynamic response of slope. The results show that under different layout schemes, the confining pressure presents a two-stage pattern of “increase-decrease”along the wall height. The displacement distribution pattern along the wall height varies with the location of the stretching belt. The horizontal peak acceleration presents a three-stage pattern of “increase-decrease-increase” along the wall height, and the maximum value appears at the top of the slope. From the slope shoulder to the depth of the slope, the settlement of the slope top increases first and then decreases in a“V”shape, and the maximum value appears at the junction of the wall and the slope. When two, three and four layers of reinforcement tape are laid, the optimal positions are (H/3, H), (0, H/3,H), (0, H/3,3H/4, H)； The plastic zone of the slope increases with the increase of the number of reinforcement zones, but the permanent horizontal displacement of the wall, the horizontal peak acceleration and the settlement of the slope top decrease gradually. The constrained confining pressure and horizontal peak acceleration of the cell at the position of the reinforcement strip increase first and then decrease from the wall to the slope. The maximum value appears at the junction of the wall and slope, and the acceleration of the wall is less than that of the wall. The cell and its packing have a certain attenuation effect on the propagation of acceleration. The results can be used to guide the seismic design of geocell flexible retaining wall under earthquake.

Abstract:In order to study the impact of sampling size and spacing on the roughness evaluation results of rock mass structural planes on high and steep slopes, a high and steep rock slope on the left bank of a certain railway station in southeastern Tibet was selected as the research area, and multi-angle approach photogrammetry technology of UAV was proposed to acquire millimeter-level point cloud data to establish a high-precision three-dimensional model of rock mass on slopes in the study area. 27 planar structural planes with point cloud information were clipped from the typical region, and the Delaunay triangulation principle was used to reconstruct the structural plane meshing. Based on this, a new method was proposed to replace the vertical projection plane in the R_S characterization method with point cloud fitting plane, and the variation law of structural surface roughness under different sampling sizes and sampling spacing was studied. The results showed that: different triangulation methods have little impact on R_S characterization values. The structural surface roughness has the size effect and the spacing effect, and the characteristic value of the roughness tends to be stable with the increase of the structural surface size, and decreases with the increase of the sampling spacing of the structural surface. Some structural planes with size effect have “false effective sampling size” and “true effective sampling size”. Therefore, the effective sampling size obtained should be “true effective sampling size” when conducting roughness evaluation.

Abstract:A real-time, efficient, and accurate grasp of road network traffic status is the premise of effective control of road traffic networks. Based on the data of the license plate recognition system at road intersections, this paper measures the road network operation status using the congestion index based on the average shortest path length and then uses the K-means clustering algorithm to classify the remaining supply of the network in different periods according to the spectral distance index and the congestion index. On this basis, according to the real-time road traffic data, the congestion index is calculated, and the real-time remaining supply capacity classification of the road network can be obtained. According to the actual remaining supply capacity of the classified real-time road network, different network traffic control schemes are designed, which can effectively alleviate traffic congestion. Taking the local road network of Changsha Wuyi Square as an example, the research results show that the local road network of Changsha Wuyi Square can be divided into four types throughout the day, and the congestion indicators are 1.2,1.3,2.207, and 3.069, respectively corresponding to good, average, poor and extremely poor remaining supply capacity of the road network. In the morning and evening rush hours, the remaining supply capacity of the network is mostly in a poor state, and the network may be in an extremely poor state in the evening rush hours. Compared with weekdays, the remaining supply capacity of the road network performs well in the rush hours on weekends. After the targeted traffic control measures are taken, the simulation results show that the total social cost of congested paths is reduced by more than 5%.

Abstract:To accurately calculate the slip of stud connectors in steel-concrete composite beams during the life cycle, the load-slip calculation model of stud connections under any number of fatigue cycles was studied. 11 push-out specimens of stud connectors were designed and fabricated to perform static slip test, fatigue slip test and residual slip test. The slip growth and distribution characteristics of stud connections during the whole process under fatigue and static load were analyzed by test results. Based on the statistical data in this paper and literature, an exponential stud load-slip model considering the ultimate slip was established under monotonic load. On this basis, considering the reduction of stud diameter and slip due to fatigue damage, and taking into account the cumulative increase in the slip of the stud connector and the degradation of its own bearing capacity, a load-slip calculation model for the whole process of stud connectors under any number of fatigue loads was established and verified by test values. The results show that the slip of stud connections can be divided into cumulative slip during fatigue loading and residual slip after fatigue loading. During fatigue loading, the cumulative slip of the stud increases in three stages of “fast-slow-rapid”. After fatigue loading, the residual slip amount and the total slip amount of the stud decrease with the increase of fatigue cycles, which indicates that the overall deformation performance of the stud deteriorates gradually due to the increase fatigue damage. The calculated values of the proposed full-process load-slip calculation model for studs are quite agreeable to the experimental ones.

Abstract:To investigate the turbulence-sand particle movement characteristics of the flow fields of a railway cutting in wind-blown sand areas and to optimize structural parameters for the protective measures, the numerical simulation analysis of the flow field with a railway cutting was carried out. Based on the Euler-Lagrange framework, the three-dimensional turbulent flow model of LES-DPM was established, and the characteristics of wind-sand flow and the movement of sand particles in the aeolian landform were studied. Two types of the protective measures were designed according to the characteristics of wind-sand movement, At the same time, the optimal design parameters of sand protection measures are obtained by comparing the flow field characteristics and sand prevention effects at different distances and different arrangements. The results show that a large number of small-scale horseshoe vortices appear in the cutting due to the concave structure, and most of the low broken velocity vortices near the rail, the turbulence structure is complex. The wind-velocity near the rail is less than 3.6 m/s, the moving particles is easily affected by the reverse pressure gradient and turbulence to settle into the cutting. The risk of sand burial is significantly increased. Therefore, it has been determined that the most effective protection can be achieved by placing a 2 m high retaining wall on the windward side at a distance of 20 m from the cutting. Most of the particles are trapped in front of the retaining wall, while those that manage to pass through settle in the backflow area behind it, with a particle size less than 0.125 mm. It has been observed that the utilization of a double-row sand retaining wall (2 m/3 m) can further expand the range of low-velocity reflux area and decrease the number of particles entering into the excavation, thereby enhancing its protective efficacy.

Abstract:To investigate the impact of single well precipitation on nearby pipelines, a calculation method of vertical displacement of adjacent pipeline caused by single well dewatering is proposed based on the Kerr foundation model and the two-stage method. In the first stage, the effective stress principle and Dupuit assumption are used to calculate the additional stress caused by dewatering in the adjacent pipeline. In the second stage, the pipeline is regarded as an Euler-Bernoulli beam resting on the three-parameter Kerr foundation to simulate the interaction between the pipeline and the soil and deduce the vertical displacement of the pipeline. The correctness of the proposed method is verified by comparing it with the results of the Winkler foundation model and the in-situ pumping test. The influences of the elastic modulus of soil, permeability coefficient, pipeline-well spacing, and water level drop depth on the vertical displacement of the pipeline are further analyzed. The analysis results show that the Kerr foundation model adopted in this paper considers the continuity of soil deformation and has more advantages than the Winkler foundation model. Soil permeability coefficient and pipeline-well spacing have little effect on pipeline deformation. However, the soil elastic modulus and the water level drop depth have a significant effect. The decrease of soil elastic modulus and the increase of water level decrease both lead to the apparent increase of pipeline deformation and easily cause pipeline displacement to exceed the allowable value. Therefore, prevention and control measures should be taken according to the corresponding factors.

Abstract:In order to obtain a reasonable seismic isolation system for typical high-speed railway simply supported bridge in nine-degree seismic regions, an analysis method for seismic hazard contribution parameter of bridge site was proposed, and a calculation method for seismic vulnerability of bridge was deduced by using kernel density estimation theory, then a seismic analysis method for railway bridge based on seismic risk assessment was established. Taking a typical 32 m prestressed concrete simply supported beam bridge in the nine-degree seismic region of Chongqing-Kunming high-speed railway line as the research object, five combined seismic isolation systems were compared and comprehensively evaluated by using the seismic analysis method based on seismic risk assessment. The results show that the seismic risk probabilities of piers and bearings can be controlled within 6% and 3% when the seismic isolation system composed of double spherical aseismic bearings, tenon-shaped metal energy dissipation devices and steel anti-drop-beam devices was used. This system can effectively improve the seismic performance of piers, dissipate the seismic energy, reduce the seismic force of pile foundations, and limit the displacement of main girders, then preventing girder falling and realizing the seismic design of 32 m high-speed railway simply supported bridge in nine-degree regions. It provides a basis for seismic analysis of similar bridges in high intensity seismic regions in the future.

Abstract:In order to explore the tensile strength and the evolution of fracture characteristics of expansive soil, this study aims to provide a comprehensive description of tensile failure characteristics. The applicability of Brazilian splitting test in the determination of tensile strength of expansive soil samples was verified by experiments. Building upon this, effects of dry density and water content on tensile strength and energy evolution during the loading of expansive soil samples were systematically discussed . The results showed that the Brazilian splitting test was suitable for remodeled expansive soil samples within the test range. The tensile strength of soil decreased with the increase of water content, and the reduction is more significant with higher dry density. Besides, the tensile strength increased with the increase of initial dry density, and the increment became smaller with higher water content. The fracture energy of expansive soil samples has a similar trend to the tensile strength, but there is a “critical water content” at which the fracture energy showed an approximate bi-linear decrease with increasing water content. Moreover, the “critical water content” increased with the initial dry density of the samples. The research results have extended the application scope of the Brazilian splitting test and provided engineering insights on using energy index as the auxiliary measures for assessing of soil resistance to destruction.

Abstract:To study the generation mechanism and variation law of ship electric field under navigation conditions, combining electrochemical principles and fluid dynamics related theories, analyzing the theoretical basis of multi-physics modeling such as turbulent flow field and ship electric field, and combining the equivalent resistance change law of the ship shafting mechanical structure in the axial frequency electric field, finally adopts the boundary element method Establish a submarine corrosion mixed electric field model under turbulent medium conditions, and analyze the changes of the ship′s electrostatic field and axial frequency electric field under different propeller speeds and medium flow rates. The results show that when the propeller speed increases from 0 to 1,2, 3,4, the electrostatic field of the ship at 2B(B is breadth of ship) directly below the propeller increases by 66.5%, 13%,3.7%, and 1.19%, and the frequency of the mixed electric field is consistent with the propeller speed. This model provides a theoretical reference for analyzing the changing law of the mixed electric field of a ship in motion.

Abstract:A new class AB operational amplifier was proposed to solve the problems of low slew rate and low gain-bandwidth product of traditional operational amplifiers for low power applications such as the Internet of Things. The current reuse technology based on differential pair transistors was proposed, which reuses the differential current generated by the input transistors. As a result, the output current of the circuit is enhanced, and the slew rate, gain-bandwidth product and DC gain are improved significantly. Moreover, differential input stages with class-AB operation and local common-mode feedback circuit are combined. As a result, the dynamic current of the output stage of the operational amplifier will not be restricted by the static current, and the larger dynamic current can be obtained under the smaller static current. The operational amplifiers is designed with a 180 nm CMOS process. For a 70 pF load capacitance, the simulation results show that the positive and negative slew rates are 23.55 V/μs and -31.47 V/μs, respectively, the gain-bandwidth product is 2.38 MHz, the DC gain is 63 dB, and the static power consumption is only 23 μW. The results show that, compared with the traditional class AB operational amplifier, the proposed circuit achieves higher slew rate, higher gain-bandwidth product and higher DC gain under lower power consumption. The proposed circuit is suitable for low power circuits and systems such as analog-to-digital converter and power management.