Abstract:In order to improve the quality control technology capability of asphalt pavement engineering, CT scanning is used to obtain the shape of coarse aggregate, generate a group of solid coarse aggregate particle models, and then use discrete element software to generate asphalt mixture simulation specimens with coarse aggregate shape and gradation composition characteristics. Digital simulation experiments are explored to achieve digital control of asphalt mixture quality.Marshall simulation specimens were generated by combining four different contact behaviors: coarse aggregate body, mortar mortar, aggregate mortar, and aggregate aggregate with the skeleton structure; The accuracy of the model specimen was verified by indirect tensile splitting test, and applied and analyzed in combination with typical quality control conditions. Taking the low-temperature performance of asphalt mixture as an example, the application analysis of simulation specimens for comparing the replacement performance of equal volume and equal mass with optimized mix proportion is carried out.The research results indicate that Marshall specimens constructed using three-dimensional discrete element method can effectively simulate indirect tensile mechanical behavior and distinguish typical conditions in the quality control process; From the perspective of splitting strength and fracture energy, it is found that the equal volume replacement method is closer to the splitting test performance of the original grade than the equal mass replacement method; The morphology of coarse aggregates with a larger particle size range is more closely related to the structure of the mixture. The solid coarse aggregate three-dimensional discrete element Marshall simulation specimen can be applied to the quality control of asphalt mixture, which has remarkable effect and can make the project management and control work more convenient and faster.

Abstract:To reveal the failure patterns considering time-dependent seismic resilience of bridge piers under zonal corrosion conditions throughout their life cycle, this study examines the time-varying degradation of key material properties, including rebar cross-sectional area, yield strength, and concrete compressive strength, under different corrosion environments and processes. Finite element models of zonally corroded piers were then established based on these computational results, and incremental dynamic analysis (IDA) was applied to obtain pier-top displacement responses. A seismic vulnerability model was constructed using a probabilistic demand model and damage threshold values. Furthermore, through Pushover analysis, the pre-earthquake time-dependent performance indicator was defined by the deterioration of pier seismic capacity over service time. The post-earthquake performance indicators were characterized by quantifying the instantaneous functional loss of the pier caused by seismic actions and subsequent recovery. Accordingly, a full life-cycle seismic resilience calculation model was proposed for piers, considering the partitioned corrosion environment. The results show that the corrosion rate of rebar in the splash zone is considerably higher than that in the underwater and atmospheric zones. Moreover, resilience degradation value of the bridge pier over a service period of 20 to 50 years is approximately twice that of the degradation value observed over 50 to 80 years. Thus, during the early service phase of piers, decision-makers can propose reasonable pre-earthquake reinforcement measures based on actual conditions to enhance seismic resilience.

Abstract:In order to objectively evaluate the bearing capacity condition of the existing subgrade and to eliminate the deviation by the popular back-calculation software due to the initial parameter values.A finite element dynamic model of asphalt pavement was established and optimized the bending basin parameters based on correlation analysis screening, so as to propose a three-parameter subgrade modulus prediction model based on BDI-F₂-d₉. On this basis, a new method was developed to conduct a multi-layer pavement modulus back-calculation, and the effectiveness and accuracy of the model were verified by using the measured data of four different typical pavement structures of the Beijing RIOHTrack. The results showed that there is a good linear relationship (R²=0.910 6) between the predicted subgrade modulus by proposed FWD three-parameter model and the measured value by the bearing plate. The ratio of them is between 0.19 and 0.28, which is consistent with the literature findings. Since this predicted subgrade modulus with more precision is utilized as an input parameter for the dynamic finite element model of asphalt pavement to simulate the real dynamic process of FWD testing, the more accurate results of the modulus of each layer of the pavement will produced by back-calculating. The research results provide the reference for the initial parameters value of modulus back-calculation software and provide the theoretical basis for back-calculation methods to calculate subgrade and each pavement modulus using DBP indexes as well.

Abstract:A domestic sea-crossing suspension bridge is a vital traffic artery connecting local islands. The massive transportation of flammable substances like LNG (liquefied natural gas) on the bridge poses a significant safety hazard to the operation of the bridge. This paper is based on existing oil pool combustion experiments in China, using the fire dynamics simulation software FDS and finite element analysis software ABAQUS to simulate LNG tanker fire and conduct the whole bridge mechanical analysis in the fire, in order to predict the structural impact of the LNG tanker fire and to provide reference for preventing and responding to emergencies of fuel tanker fire on the bridge. The simulation is aiming at a small probability fire accident of two LNG tankers rear-end burning in the middle of the main span of the bridge. The simulation results show that when an LNG tanker fire occurs on the bridge, the main cable and some slings are directly affected by the fire: the main cable loses part of the structural performance and two slings are damaged by heat and fail. In addition, the bridge deck pavement in high temperature area is also damaged by high temperature and the main beam steel structure under the pavement is relatively less affected by heat. The deflection of the bridge increases 0.234 m in the fire, and the forces on the east and west sides of the bridge are no longer balanced. According to the fire prevention research on key components in the high temperature area in the fire, the heat transfer analysis of ABAQUS shows that main components of the bridge can be effectively protected in the fire by the design of a double-layer 5 mm thick thermal insulation aerogel protective layer.

Abstract:The load-shedding culvert changes the transmission path of the fill load on the culvert roof, causing the fill load to concentrate on the load shedding blocks, thereby reducing the earth pressure on the culvert roof. However, the soil and compressible material in the load shedding hole will creep with time under long-term fill load, leading to stress redistribution. In order to clarify the variation law of earth pressure and load reduction effect of the load-shedding culvert under the long-term fill load, the model test on rigid foundation was used to explore the load transfer law of the load-shedding culvert during the sand filling construction, and the correctness of the numerical model was verified according to the test results. Then the verified numerical model was conducted to analysis the long-term variation law of earth pressure of the load-shedding culvert by considering three different creeps conditions (i.e., the creep of EPS material in the load shedding hole, the creep of embankment fill, and both creeps). The results show that, on rigid foundation, considering the creep of EPS slab, the earth pressure at the top of the culvert decreases by 25.4% in the 30 years of post-construction compared with that at the end of soil filling, the load reduction effect of the earth pressure at the top of the culvert increases with time, it suggests that the vertical earth pressure coefficient on the culvert top can be taken as 0.45. When considering the fill creep or both creeps, the earth pressure at the top of the culvert fluctuates and finally approaches to the self-weight pressure of the fill soil, the load reduction effect gradually decreases with the increase of time, it suggests that the vertical soil pressure coefficient on the culvert roof can be taken as 1.1. For cohesive soil embankment, if the earth pressure redistribution caused by fill creep is not considered in the engineering design, the load reduction effect of the load-shedding culvert probably be overestimated and resulting in structural damage.

Abstract:Large cantilever prestressed concrete bent caps (hereinafter referred to large cantilever PC bent caps) typically incorporate corbels at the root of the cantilever to ensure the mechanical behavior. However, there is currently a lack of a rational framework for determining the appropriate size of these corbels. In this paper, the shear stress calculation theory of large cantilever PC bent caps with corbels is proposed by equating the corbels to arc segments; a 1∶4 scaled model experiment is carried out to analyze the influence of corbels on the shear stress distribution and stress performance of the cantilever root; The formula for calculating the minimum corbel length ratio under different design parameters of compression edge inclination, cantilever lengths and prestressing level is given according to the bending and shear strength requirements. The findings indicate that the shear stress calculation theory proposed in this study for variable cross-section beams with corbels provides a more accurate representation of the impact of corbels on the longitudinal distribution of shear stress. Additionally, the most critical location for shear stress has shifted from the cantilever root to the changing position of bottom inclination. Furthermore, as the corbel length ratio increases, the stress peaks at the upper and bottom edges of the beams decrease. Therefore, it is essential to control the size of the corbel to ensure the strength of the compression edges. The formula for the minimum corbel length ratio, as presented in this paper, ensures its effective accuracy when applied to large cantilever PC bent caps with varying parameters. This formula demonstrates practicality in construction applications.

Abstract:To improve the energy dissipation efficiency and optimize the geometric parameters of a new type of butterfly-shaped steel plate damper, the calculation formulas for the initial stiffness and yield capacity of the new damper were firstly derived. Then, quasi-static tests were conducted on 8 damper specimens to comparatively investigate the failure modes, mechanical parameters, and hysteresis performance. Finally, through numerical simulation analysis of 67 models, the influence of parameters such as the width ratio a/b and height thickness ratio H/t of the energy dissipating ribs, number of energy dissipation ribs n, and number of steel plates N on the mechanical performance of the damper was explored. The results show that the mechanical performance of the new damper is stable with a plump hysteretic curve. The ultimate drift of the damper is greater than 10%, and the maximum equivalent viscous damping ratio exceeds 0.4. The mechanical performance of the damper is proportional to the number of energy dissipation ribs n and the number of steel plates N, which is convenient for standardized design. The initial stiffness, yield strength, and equivalent yield displacement of the damper can well be predicted by theoretical analysis, and the average calculation errors of the theoretical formulas are 14.0%, 8.4% and -10.9%, respectively. By designing the size of the energy dissipation ribs reasonably, the deformation state of full-section yielding can be achieved, resulting in a maximum energy dissipation per unit steel volume of 0.217 J/mm³. When the geometric parameters of the energy dissipation ribs satisfy the requirements of a/b=0.25-0.50 and H/t=20-30, the optimal energy dissipation economy of the new damper can be realized.

Abstract:To study the dynamic water storage performance and evolution mechanism of fractured rock mass in the caving zone under overburden pressure, lateral compaction tests were performed on fractured rock samples of coarse sandstone, sandy mudstone, and mudstone with a self-developed visualization device. The porosity, bulking coefficient, and spatial evolution images of the entire compaction process were obtained. The experimental results indicated that the compaction process of fractured rock mass can be divided into four stages: large gap compaction, small gap compaction, post failure compaction, and compaction strengthening. Among them, the changes in water storage space of rock mass mainly occur in the first and third stages. Due to differences in rock mass strength and water softening characteristics, the three types of fractured rock contain different compaction processes and segmented characteristics, resulting in water storage spaces in sandy mudstone being 3.75 and 7.5 times larger than those in coarse sandstone and mudstone, respectively. As particle size increases, the stability of the fractured rock mass improves, with porosity increaasing by 0.0,0.09, and 0.04 for coarse sandstone, sandy mudstone, and mudstone, respectively. The experimental results can be well explained by particle mechanics, where the compaction process of rock mass is essentially characterized by the formation of slip, compression, and force chains among loose rock blocks. Variations in lithology, overburden pressure, and particle size distribution result in differences in the order and process of occurrence of the three stages, which in turn leads to differences in the water storage characteristic of the rock mass. The research results can provide theoretical support for the accurate evaluation of water storage capacity of underground reservoirs in coal mines.

Abstract:The design parameters are primarily determined empirically for the concrete overlay of steel-concrete composite bridge decks, as the lack of a clear stress analysis mechanism can lead to structural cracking or inefficiency. The transverse performance of the concrete overlay was simulated as a infinitely long beam on an elastic foundation based on the characteristics of orthotropic composite bridge deck. A theoretical analysis model was first established for the transverse behavior of the concrete overlay under wheel load, and the formulas were derived for the deformation, load, and effective range of the wheel load. A full-scale model static load test was then designed and conducted according to the practical orthotropic composite bridge deck. A corresponding spatial finite element model was also established, and the theoretical, experimental, and finite element results were compared to validate the accuracy of the proposed mechanical model. Due to the constraints imposed by the diaphragm and the rigid concrete layer, the torsional deformation of the U-rib under eccentric loading can be neglected. The effective range of the wheel load is limited to the span of 5 U-ribs. Parameter analysis indicated that both the arrangement of studs and transverse diaphragms have a significant influence on the transverse deflection of the concrete overlay. Within the range of commonly used design parameters, the proposed calculation formula is applicable to the design of steel-concrete composite bridge decks.

Abstract:In order to tackle traffic congestion and safety issues in expressway merging areas and to ensure efficient, safe, comfortable, and stable travel of connected and automated vehicles (CAVs) in these areas, this study employs the DQN (deep q-network) algorithm from deep reinforcement learning. By considering factors such as vehicle safety, efficiency, and comfort, a reward function model for neural network training has been established, and a CAV lane-change decision-making method for merging areas has been proposed. Using the open-source highway-env simulation scenario, a simulation environment for expressway merging areas has been set up, and experiments have been conducted on the mainline and ramps. The results of the simulation experiments show that compared to the intelligent driver model (IDM) and the lane-change decision-making method in highway-env, the proposed CAV lane-change decision-making method enables CAVs to quickly reach a stable driving state at a speed of 22.22 m/s. It also reduces frequent lane changes and acceleration/deceleration behaviors, and optimizes the time-headway between vehicles. This significantly improves the efficiency of traffic flow and ride comfort. The research findings provide a new method for vehicle traffic management in urban expressway merging areas under intelligent networked conditions. They also offer a decision-making approach for lane changes in future connected and automated vehicles.

Abstract:In order to explore the migration law of lead ions in unsaturated loess under freeze-thaw cycle condition, this paper conducted adsorption experiment and soil column experiment on lead ion migration under freeze-thaw cycle condition. Based on the principle of heat mass conservation, a coupled mathematical model for pollutant migration in unsaturated soil was established. At the same time, the COMSOL multiphysics simulation software was used to numerically solve the model. The reliability of the coupled model was evaluated in combination with soil column experiment, and the variation laws of various physical quantities were explored. Research has shown that under the freeze-thaw cycling condition, the temperature change of the soil column lags behind the change in cycling temperature. Although freeze-thaw cycling significantly reduces soil permeability and sharply decreases liquid water flux, the decrease in liquid water flux does not completely hinder the migration of pollutants to the freezing zone. Ionic diffusion can also cause pollutants to appear in the frozen zone of the soil, leading to an increase in the adsorption concentration of pollutants in the frozen zone. At 96 hours, the mass concentration of pollutants at the top of the soil column reached 0.204 g/L, and the adsorption concentration of pollutants reached 3.62×10^-7 kg/kg; Under freeze-thaw cycle condition, pollutant crystallization occurs at the lower part of the soil column, with a maximum crystal volume content of around 4%. At the same time, the expansion caused by pollutant crystallization accounts for about 9% of the total soil displacement, which is much smaller than the expansion displacement of ice crystals. The negative temperature gradient decreases, the solubility of pollutants increases, and some of the precipitated pollutant crystals dissolve again. Some of the ice crystals also melt again, and the combination of the two causes the displacement of the soil column vertex to slowly increase in a wave like manner.

Abstract:To explore the broken expansion and water storage evolution characteristics and internal mechanism of typical rock masses in goafs during mining, a synchronous test method of broken expansion coefficient and water storage coefficient based on a self-developed rock triaxial fluid-solid coupling test system was developed. A triaxial loading test was conducted on rock samples of coarse sandstone, siltstone, and mudstone to determine the broken expansion and water storage coefficients in complete stress-strain process, and the spatial distribution of internal fractures in the rock was synchronously obtained via nuclear magnetic resonance imaging. The results show that the broken expansion and water storage coefficients of the three types of rock samples gradually increase and tend to stabilize with the loading process, and the corresponding stress-strain curve shows a phased gradient change in four stages. Among them, the water storage coefficient exhibits a good Weibull distribution with strain variation. The initial porosity affects the expansion morphology of newly formed fractures and the water storage space of rock samples to some extent. As the initial porosity of rock samples increases, the water storage coefficient shows a linear increasing relationship before 80% prepeak, and then an exponential increasing relationship. The theoretical value of the water storage coefficient calculated based on the expansion coefficient is consistent with the evolution law of the experimental measured value, but the difference in value can reach up to 0.7%, indicating a clear characteristic of first broken expansion followed by water storage. The broken expansion and water storage coefficient of rock samples are influenced by the coupling effect of stress loading and initial porosity. In the initial stage of loading, the initial porosity dominates, gradually transitioning to stress dominance, and is ultimately determined by both stress and the degree of penetration of rock pores and fractures.

Abstract:The study investigates dynamic response of vehicles driving on mountainous roads by developing a three-dimensional (3D) road roughness model using the random sine wave superposition method, integrated with MATLAB and TruckSim software. The roadbed structure is modeled as an infinite multi-layer plate on a viscoelastic half-space foundation. The three-dimensional interaction forces between the vehicle and the road, as well as the vehicle′s driving dynamics, are analyzed during the continuous uphill operation of a three-axle loaded vehicle. A self-developed generalized integral calculation program is employed to determine the vertical displacement of a four-layer pavement. The results reveal significant differences between 3D and 2D pavement models in terms of the maximum and root mean square values of longitudinal and lateral forces, with the lateral force on 3D pavement being 42.95% higher than on 2D pavement. When navigating circular ramps, the three-dimensional interaction forces exhibit notable variations. Specifically, when traversing a concave ramp, the peak longitudinal force can exceed the average longitudinal force by up to six times, while the lateral force demonstrates a pattern of initial increase, followed by a decrease, another increase, and eventual stabilization. Furthermore, the displacement impact of multiple tires on the road is not simply additive but must be evaluated based on factors such as tire position and effective distance. The findings provide valuable technical insights for the operation of heavy vehicles in scenarios involving continuous slope climbing, arch bridges, and culverts.

Abstract:The balconies of fourth-generation buildings are covered with a large number of vegetations, resulting in a noticeable alteration of their aerodynamic profiles. The airflow is disturbed by the vegetation, leading to more complex variations in wind pressure on the building surfaces. To investigate the influence of vegetations on the non-Gaussian characteristics of wind pressure on high-rise buildings, rigid model pressure tests were conducted to analyze the probability distribution of extreme wind pressures and standardized wind pressure coefficients on the building facade under different coverage areas of vegetations. Empirical criteria and distribution characteristics for non-Gaussian wind pressures were provided, revealing the influence of vegetation on extreme wind pressures on the building facades. The results indicate that the presence of vegetations changes the separation point position of incoming flow on the windward side of the building, causing the edge measurement points to transform from non-Gaussian to Gaussian. Conversely, crosswind wind pressure shows non-Gaussian, which is less affected by vegetations. The extreme wind pressure on narrow surfaces is less affected by vegetations, while vegetations arranged on relatively wide facades have a greater impact on the flow field in the area. The reduction of extreme wind pressure is more significant under different vegetation coverage rates. Furthermore, the effectiveness of greenery in reducing extreme wind pressures initially increases with the coverage area, reaching its maximum reduction effect at a coverage of 13.5%. The results can provide reference for wind-resistant design of similar structures.

Abstract:In order to analyze the characteristics of axial distribution of borehole wall pressure along the borehole in rock blasting, the axial distribution of borehole wall pressure along the borehole of coupled charges with different borehole diameters was studied by combining theoretical analysis, model testing, and finite element simulation. Firstly, based on the theory of spherical detonation wave, a model of the detonation wave propagation in the borehole was established. Based on the relationship between the incidence angle of the detonation wave and the diameter of the borehole, the theoretical calculation formula of the borehole wall pressure under different propagation stages of detonation was derived, and the change curve of the borehole wall pressure along the axial borehole wall with different borehole diameters was obtained. In order to verify the rationality of the theoretical analysis, the concrete thick wall cylinder model test was further used to monitor the pressure of the borehole wall by using a high-speed multichannel dynamic strain test system. Meanwhile, finite element numerical simulation of different borehole diameters was established to obtain the axial distribution of borehole wall pressure results of different borehole diameters. And the model test and numerical simulation results were compared with the theoretical analysis results. The results show that the coupled charge borehole wall pressure presents an uneven distribution along the axial direction of the borehole, and the borehole wall pressure near the detonation point increases sharply, begins to decrease exponentially after reaching the maximum peak pressure, and finally tends to fluctuate steadily. There is a positive correlation between the borehole wall pressure and the borehole diameter. The maximum peak pressure and the stable fluctuation stage of the borehole wall pressure increase with the borehole diameter. The relative error between the theoretical calculation value of the axial borehole wall pressure at d=40 mm and the results of the model test and numerical simulation is small, which verifies the rationality of the theoretical analysis.

Abstract:Marshy-lacustrine clays with bonding characteristic, soil structure and initial anisotropy were formed by shrinkage of lake wetlands and ancient lake wetlands. In order to effectively describe the stress-strain relationship and yield characteristics of marshy-lacustrine clays, an elastic-plastic constitutive model of soil taking into account evolution of bonding strength, soil structure and initial anisotropy effects was established. A bonding strength evolution law used for three stress states including isotropic compression, shear and a combined action of compression and shear was proposed, based on the variation law of bonding strength under shear stress path and the corresponding relationship between yield surfaces and bonding strength with isotropic compression. On the basis of the Modified Cambridge model, the hardening law was improved by considering the evolution law of bonding strength and the influence of volumetric strain hardening and shear strain hardening. To reflect the effect of initial anisotropy, anisotropic parameters η_NCL was introduced and polar coordinate transformation was performed for the p′-q space. A structured and anisotropic constitutive model considering bonding for soil was presented by using the correlated flow rule. All parameters of the structured and anisotropic constitutive model considering bonding can be obtained through isotropic compression tests, triaxial test, and K₀ consolidation tests. The comparison between model predictions and experimental results shows that the proposed model can reasonably capture the influences of bonding strength, soil structure and initial anisotropy on the stress-strain and yield characteristics of marshy-lacustrine clays. The structured and anisotropic constitutive model considering bonding for marshy-lacustrine clays can effectively reflect the gradual degradation of bonding strength during loading and the improvement of bonding strength on soil tensile strength under unloading stress path. This model takes into account the influence of bonding strength, soil structure and anisotropy, which can reasonably characterize the mechanical response of marshy-lacustrine clays.