Abstract:

To effectively investigate the fatigue performance of stabilized soil base， a framework combining analytical models and numerical simulations that considers field humidity distribution was proposed in this paper. First， based on the solution of equilibrium matric suction and the estimation of the resilient modulus， the nonlinear mechanical properties of the material caused by stress dependence and moisture sensitivity inside stabilized soil roads were characterized. Subsequently， based on the energy-based mechanistic（EBM） approach and the damage mechanics theory， the fatigue performance simulation of unsaturated stabilized soil was constructed. Finally， the PDE-FE method in Comsol Multiphysics was used to conduct the multi-field coupling simulation analysis of the fatigue performance of unsaturated stabilized soil base. The results show that the framework proposed could effectively simulate the fatigue damage analysis of stabilized soil base under field humidity distribution.

Abstract:

To address the discrepancies between existing laboratory aging simulation methods and the actual aging gradient and service temperature of asphalt pavements， this paper proposed a novel indoor long-term aging method based on the pure oxygen accelerated aging， aiming to simulate the aging behavior of asphalt mixtures at service temperatures. The investigation of the aging properties of asphalt mixtures with time and space was conducted using Fourier transform infrared spectroscopy（FTIR） and dynamic shear rheometer（DSR）. The results show that the novel aging method proposed can effectively simulate the aging behavior of compacted asphalt mixtures within the service temperature range， achieving an aging degree close to that of standard long-term aging tests. With the increase of aging time and temperature， the aging degree of AC-13 and SMA-13 mixtures both increases， and the aging degree of SMA-13 mixtures is only 1/5 of that of AC-13 mixtures. Concurrently， the high temperature performance of the two mixtures increases， while the fatigue life decreases. With the increase of aging depth， the aging index and high-temperature performance of AC-13 and SMA-13 mixtures gradually decrease， whereas the fatigue life significantly increases. Under different aging conditions， SMA-13 mixtures show a superior aging resistance and fatigue resistance than AC-13 mixtures， particularly at low strain levels. ANOVA indicates that the aging time significantly impacts the sulfoxide index and high-temperature performance， but has no significant effect on the carbonyl index， high-temperature performance， and fatigue life. The aging depth only significantly impacts non-recoverable creep compliance at 0.1 kPa， with no significant effects on the other evaluation indexes.

Abstract:

In response to the insufficient reliability of material mechanical parameter values in current asphalt pavement design， and based on the tensile and compressive difference characteristics of road materials， this paper conducted a study of nonlinear characteristics and quantitative relationship of tensile and compressive parameters of asphalt mixtures under the influence of multi-factor coupling. The results show that the tensile and compressive stress-strain characteristics of asphalt mixture in the elastic stage conform to the bilinear characteristics of the bi-modulus theory. The tensile and compressive mechanical parameters first increase sharply with the increase of loading speed and then tend to flatten out， and show a power function relationship. It has a negative exponential relationship with temperature， and the higher the temperature increase， the greater the decrease in mechanical parameters. The relationship between the asphalt dosage and the exponential decay model function is that the change in asphalt dosage at high temperatures （>30 ℃） has a relatively small impact on the mechanical parameters. The asphalt dosage corresponding to the maximum mechanical parameter is basically consistent with the optimal asphalt dosage obtained from the Marshall test. In terms of the degree of influence， temperature has the greatest influence on the mechanical parameters， while factors have the most significant effect on strength. The tensile strength parameter is more sensitive than the compressive strength parameter， based on which the quantitative value model of the tensile and compressive parameter of asphalt mixtures under the influence of multifactorial coupling has been established. At the specification common temperature of 15 °C （20 °C）， the ratio of compressive strength to tensile strength and the ratio of compressive modulus to tensile modulus can be 6.5 （7.5） and 1.6 （1.7）， respectively. The ratio of compressive modulus to compressive strength and the ratio of tensile modulus to tensile strength can be 400 （1 700） and 450 （2 000）， respectively.

Abstract:

Based on the potential physicochemical spatial crosslinking properties of SBS modifier and polyurethane-precursor chemical modifier（PRM）， the SBS-PRM composite modified asphalt was prepared. The high viscosity characteristics of the asphalt samples were clarified by penetration， softening point， ductility， and dynamic viscosity test. Rheological characterization of modified asphalts was investigated using frequency sweep test， multiple stress creep recovery test， linear amplitude sweep test， and bending beam rheometer test. The physicochemical composite modification mechanism was explained using Fourier transform infrared spectroscopy， atomic force microscopy， and fluorescence microscopy. Finally， the pavement performance of asphalt mixtures was verified. The results show that PRM changes the molecular structure of asphalt through chemical reaction which contributes to improving the compatibility of SBS with asphalt. The formation of spatial crosslinked network structure enhances the viscosity， resistance to high-temperature permanent deformation， low-temperature cracking， and fatigue damage of asphalt. In addition， significant advantages are obtained in high temperature rutting resistance， low temperature cracking resistance， and moisture damage resistance of SMA-13 mixtures prepared with composite modified asphalt.

Abstract:

In order to deal with the problem of backfilling in the narrow area of the underpass in the high-load flight area， a large amount of construction waste and silt produced by the reconstruction and expansion of Jinan Yaoqiang Airport was used as the main aggregate to prepare the controlled low-strength materials（CLSM） with the characteristics of high fluidity， self-compaction， and high strength. The test results show that the strength of the test group mixed with construction waste or stone debris increases significantly compared with the only silt used. The modification effect of construction waste is about 80% higher than that of stone debris. It is more economical to add construction waste than stone debris， but not for the increase of the cement content. The dry - wet cycle strength of the best mix ratio decreases and stabilizes at about 1 MPa， with the mass loss rate stabilizing at about 1%. The compression performance is the same as soil with a 6% cement quality score， and the compressive deformation after the dry - wet cycle is much less than that of silt， which meets the long-term bearing requirements of the foundation in flight area.

Abstract:

This paper designed a skeleton dense recycled brick-concrete materials（RBCM） using recycled brick-concrete materials. The mechanical characteristics of RBCM under compressive， tensile， and penetration stresses were synthesized by various tests. Considering the actual working conditions， two types of durability environments， i.e.， the specimen cycle and the particle cycle， were designed， and the durability evolution of RBCM was quantified by an unconfined compressive strength test. The engineering application performance of the RBCM cushion was verified based on the field test section. The results show that the permeability of the RBCM cushion is poor， and it is appropriate to pave a permeable cushion on the upper part of RBCM cushion. The increase in cement content significantly improves the compressive strength and failure mode of RBCM， the compressive strength and penetration strength are higher， but the tensile strength is lower. The durability coefficient of RBCM after 30 cycles is still more than 50% after adding a little cement. Even without cement， the compactness and mechanical properties of the RBCM cushion still meet the requirements of the current cushion design index.

Abstract:

This paper established a simplified vehicle-bridge coupling model of urban viaduct via nonlinear contact element to simulate the contact relationship between vehicle tires and bridge deck， and to investigate the influence of vehicle mass， frequency， ground motion spectrum characteristics and peak acceleration on the dynamic response of vehicle-bridge system subjected to selected vertical ground motions with wide-range of spectral characteristics. The results show that the vehicle mass， vehicle vibration frequency， and ground motion spectrum have a great influence on the vehicle bridge coupling system. The vehicle bridge separation phenomenon occurs in 221 of 1 866 cases. Vehicle bridge separation is unfavorable to the displacement response of the bridge in most cases， and also greatly increases the impact force on the bridge deck. Statistically， the average value of peak acceleration of vehicle bridge separation increases with the increase of vehicle mass， decreases with the increase of vehicle frequency， and decreases with the increase of average period of ground motion.

Abstract:

The influence of the appropriate spacing between reinforcement and ballast on the performance of pullout resistance in multi-layer reinforced soil structures were explored. By improving the conventional single-layer geogrid-ballast pullout numerical test model， discrete element simulations of synchronized pullout under equivalent displacement amplitudes for multi-layer geogrids were achieved. The rigid clump particles were used in the numerical model to mimic the non-spherical characteristics of the ballast particles， and bonded particle strings were incorporated to simulate the uniformly loaded triaxial geogrid， by considering both particle interlocking effects within the ballast and the tensile behavior of the geogrid. Using criteria such as average pull-out force， interfacial strength at specific layer positions， and strain in the reinforcement， the interfacial coupled behavior between multi-layer geogrid-reinforced ballast was scientifically determined， and the interlayer interference mechanism within the system was investigated at the particle scale. The results show that the pull-out force and its rate of increase in multi-layer geogrids are lower than those in single-layer geogrids， especially at high normal stresses， and there is non-uniformity. As the number of reinforcement layers increases， significant differences in the resistance of the reinforcement are observed， along with an increase in the frictional energy dissipation. Overlapping interlayer particle displacements weaken the macroscopic mechanical response of the reinforcement because of insufficient development of particle force chains. Subsequent investigation of normal contact forces indicates that inter-layer interference in multi-layer geogrid-reinforced structures may lead to instability in the distribution of normal contact forces.

Abstract:

This paper proposes three types of tuned mass damper（TMD）， i.e.， cross shaped mass damper （CTMD）， X shaped mass damper （XTMD）， and tourbillion shaped mass damper（TTMD） with free motion in the plane. The stiffness changes， modal， and vibration responses under harmonic excitation of the three TMDs are compared and analyzed using the finite element model. The analysis results indicate that when the excitation direction of a TMD is perpendicular to the spring， the spring force exhibits a nonlinear behavior， and compared with other TMDs， TTMD has a better robustness and higher utilization efficiency. When the mass ratio is greater than 3%， the vibration suppression of TTMD is more significant.

Abstract:

To address issues such as slag dumping and limited slag transportation under the action of upper vacuum dewatering， a dewatering method of applying a vacuum load at the bottom of the waste slurry is proposed. A series of model tests were conducted on waste clay slurry under four different dewatering loading conditions by using a self-developed dewatering device that can apply a vacuum load at the bottom of the waste slurry. The rule of physical quantities such as settlement at the interface between slurry and water， pore water pressure， water content， and the total amount of water discharged after dewatering are analyzed. The results show that the fourth dewatering loading method has the best dewatering performance. After the fourth dewatering loading method was used to dewater the waste clay slurry with an initial water content of 103.00%， the water content distribution range was 37.10%?62.65%， and the minimum internal pore water pressure was -73.09 kPa， which was close to the vacuum value of -80.00 kPa applied at the bottom. In addition， compared with the other three dewatering loading methods， the average settlement was increased by 106.40%， 2.91%， and 6.15%， respectively， and the total amount of dewatered water increased by 122.0%， 8.0%， and 5.1%， respectively. Meanwhile， a numerical calculation model for vacuum dewatering of waste clay slurry is provided based on piecewise-linear finite difference CS2 model. The sedimentation at the slurry-water interface during the dewatering process of waste clay slurry was numerically simulated， and the effectiveness of the numerical calculation model was verified.

Abstract:

Different consideration methods of vegetation model are introduced， which are discussed from water flow resistance， bed resistance， vegetation growth and so on. Based on hydrodynamic and sediment transport numerical models of engineering scale and laboratory scale， the research progresses in flow velocity， turbulent energy， coherent structure， wave propagation characteristics of different incident wave shapes， suspended sediment concentration， and morphological evolution influenced by vegetation are reviewed. Combined with a lot of numerical model study， the future research prospects are proposed.

Abstract:

This paper selects the most basic “one-fold” plane as the research object for office buildings. It takes basic parameters such as width， depth， and angle as the boundary conditions to generate the plane shape by collecting the data of polyline cases mainly in Hangzhou and Shanghai. Using Python tools for mathematical modeling， it generates different forms of “one-fold” plane building models. Using the Designbuilder energy consumption software based on the EnergyPlus platform， it dynamically simulates the annual energy consumption of each model. Using the Spearman coefficient method for correlation analysis， it obtains two plane morphological parameters that have the greatest impact on energy consumption， the width-to-depth ratio M₁， and the oblique depth M₂. Finally， performing regression fitting and regression evaluation on the model data， it obtains the changing trend of the mutual mapping between the morphological parameters M₁， M₂ and the total energy consumption E₁， and draws the contour map of M₁-M₂-E₁ accordingly.

Abstract:

This paper aims to quantify the spreading risks of infectious disease in public transport vehicles under various distributions of the passengers. Using the spreading characteristics of COVID-19 in 2020 as an example， first， the patterns of customized bus seat choice behaviors before and after the outbreak of the disease ranging from 2019 to 2020 were analyzed. Then， based on weighted encounter network， a susceptible-exposed-infectious-recovered（SEIR） model for epidemic dynamics was constructed， while the risks of spreading of disease with various distributions of passengers were studied. Finally， a comparative analysis was conducted to quantify the impacts of different infectious disease control policies such as seat assignment optimization， ridership control， and personal protection guidance. The results demonstrate that at the beginning of the outbreak of the diseases， customized passengers spontaneously increase their distances by 15% which effectively reduced the risks of infection by over 30%. In terms of the epidemic control policies， in addition to personal protection with significant impacts on reducing the risks， the implementation of ridership control with seat assignment can also largely decrease the risks of spreading of infectious disease in public transport systems. With the optimized allocation of seats， using the current average ridership as the reference， the risk of infection may decline by about 40%.

Abstract:

In order to improve the matching accuracy between the compressor and the turbocharger under the unsteady flow condition， the internal joint operation law method was proposed based on the turbocharger operating conditions， and the unsteady flow characteristics of the compressor with different structures and performance correction were studied. The results shows that among the three structures of compressors， except for the high speed and high flow rate joint point operation condition， the unsteady flow performance of the equal-length blade compressor with a 1 mm reduction in inlet diameter has obvious advantages and a better surge performance. After the correction of compressor performance based on the unsteady coefficient， the performance of the compressor was closer to the real working condition.

Abstract:

This paper investigates the effects of turbulence model parameter， one-way coupling model parameter， and break-up model parameters on spray penetration and droplet size based on the VOF-spray one-way coupling model. The results indicate that the RANS constant C_ε1 and the RT model size constant C_RT have the greatest effect on the spray penetration， and size constants C_KH and C_RT have the greatest effect on the droplet size. Based on the above analysis， it establishes a high precision spray model for different working conditions. The error between experiment and simulation is within 3% for standard Spray G condition， and around 10% error for different ambient gas densities.

Abstract:

Different nonlinear acoustic impedance models at high sound intensity are compared， and the influence of incident sound pressure on the acoustic impedance are investigated. An improved transfer matrix method is proposed to calculate the acoustic impedance of double-layered perforated panels. A comparison of the calculation by different nonlinear acoustic impedance models and experiment results at different incident sound pressure levels indicates that the results obtained by the Park model and the Maa model agree with the measurement results well when SPL is lower than 140 dB， while Laly model can get better results when SPL is 140–150 dB. For structure composed of double-layered or multi-layered perforated panels at high sound intensity， according to the improved transfer matrix method， the sound pressure level of each layer is calculated by transfer matrix， and acoustic impedance of each layer is calculated based on sound pressure level and perforation parameters. Results of double-layered perforated panels calculated by improved transfer matrix method coincide with measurement results for incident sound pressure level at 120–150 dB.

Abstract:

Based on the transfer matrix method， the calculation of absorption of multi-layer micro-perforated panels（MPP） is conducted. Properly increasing the number of layers with different impedance in given cavity depths can improve sound absorption performance. The 4-layer and 5-layer micro-perforated panels with optimized parameters obtained by genetic algorithm can significantly broaden the sound absorption frequency bandwidth and improve the absorption coefficient of the whole frequency range， with an average absorption of 0.7 and 0.8 respectively in the range of 200–3 150 Hz which covers the main noise frequency range of high-speed train at 250–350 km?h^-1 . For 5-layer absorbers， absorption coefficients can be higher than 0.8 at 400–4 000 Hz.

Abstract:

This paper addresses key issues such as difficulty in describing window geometry and structural parameters by combining building point clouds with facade image. It uses machine learning algorithms to identify and extract windows in the image， and performs line feature extraction and fitting on the window image to obtain the required window structure type. In addition， it conducts grid division and window contour extraction on the building point cloud to obtain the required geometric parameters. Moreover， based on the extracted structure type and geometric parameters， it retrieves the model template from the window model library and modified to achieve efficient modeling of building windows. The windows extraction accuracy of the proposed method can reach 89.5%， and the geometric accuracy is within 5 cm.