Study On Mechanical Behaviours Of Asphalt Pavement Structures Under The Braking Force Of BRT Buses

The rapid development of urban public transportation has promoted economic and cultural exchanges and facilitated the travel of citizens.As a new type of public transportation,BRT effectively relieves the pressure on urban traffic and is also conducive to the improvement of urban air quality.The rut,crack,mud-pumping and other diseases occurred on the asphalt pavement are related to driving comfort and driving safety.The in-depth study of the mechanical response of the asphalt pavement under the temperature field and the dynamic load and the causes of the disease formation are important to improve the asphalt pavement performance.This paper uses Lanzhou BRT asphalt pavement as the background and uses the ABAQUS finite element software to build a three-dimensional finite element model to analyze the temperature field,temperature stress,and the dynamic response of the pavement structure under the action of temperature field and moving load.The development rules of rut and crack on asphalt pavement are discussed.The main work is summarized as follows:(1)Select the typical meteorological conditions in Lanzhou in summer and winter to calculate the temperature field and temperature stress distribution of the pavement structure.By setting the thermophysical parameters of the asphalt mixture of surface layers with different levels,including heat capacity,solar radiation absorption rate,and road emissivity.The effects of changes in various physical parameters on the distribution of high temperature fields in summer are analyzed.Studies show that increasing the thermal capacity and pavement emissivity of asphalt mixtures and reducing the solar radiation absorption rate can reduce the temperature of asphalt pavements.(2)Taking the area near Lanzhou BRT station as the research scope,the user subroutines—DLOAD and UTRACLOAD written in Fortran language was used to simulate the BRT braking pit stop process,and the summer temperature field result file was imported into the three-dimensional finite element model.The influence of initial speed of the brake on typical mechanical indicators of asphalt pavement is analyzed.In addition,the effect of rutting formation under continuous temperature changes is analyzed through the load action method of "replacing motion with static".Research shows that each dynamic response index increases at the same time as the initial speed decreases.The peak duration of normal stress and shear stress at each structural layer increases with the decrease of the initial speed.The decrease of the initial speed and the increase of the horizontal load during BRT braking can increase the degree of road surface depression and uplift.(3)Set longitudinal surface cracks and transverse surface cracks at the edge of the model load zone and the cross section in the model respectively.Call the user subroutines—DLOAD and UTRACLOAD to implement the process of BRT braking pit stop,and use displacement extrapolation to calculate the stress intensity factor under the combined action of temperatureand load.The research shows that the longitudinal surface cracks are propagated mainly by type ? cracks,supplemented by ? and ? cracks,and the transverse surface cracks are propagated by type ? cracks and supplemented by ? cracks.The changes of initial velocity,temperature field,and horizontal load coefficient during BRT braking process can affect the crack stress intensity factor.