Study On Dynamic Amplification Factor Of Highway Bridge Under Random Traffic Flow

In order to reflect the vehicle-bridge coupling vibration effect in bridge design,the dynamic amplification factor is usually multiplied by the static response of the bridge under the action of vehicles to simplify the effect of vehicle-bridge coupling vibration.Scholars’ research on dynamic amplification factor or the design specifications of bridge dynamic amplification factor in different countries and regions mainly focus on the action of a single vehicle.In fact,bridges are subjected to complex traffic flow,and traffic flow parameters such as vehicle type,vehicle speed,vehicle weight,and vehicle spacing have strong randomness,which makes the impact effect of bridges under random traffic flow load completely different from that of single vehicle,and most bridge dynamic amplification factor design codes do not distinguish different bridge types.Therefore,obtaining a more accurate bridge dynamic amplification factor is very important for bridge design and construction monitoring.Therefore,the main research work of this paper is as follows:(1)The three lanes random traffic flows are simulated based on cellular automata(CA),and the traffic flow is subdivided into three different types: dense,moderate,and sparse according to the Greenshields relationship model,which can accurately simulate and analyze the actual driving conditions.(2)According to the power spectrum expression of road roughness given by the international standards association(ISO),the inverse Fourier transform is carried out to generate the road roughness,and the dynamic coupling equations of 2-axis,3-axis,4-axis,5-axis,and 6-axis vehicles and bridges are deduced.The decoupling program is compiled based on the whole process iterative method and the joint simulation of numerical analysis software MATLAB and finite element software ANSYS,and the results of classical examples show that the analysis program is correct.(3)This paper analyzes the difference of dynamic amplification factor of a simply supported beam under the action of single vehicle and moderate traffic flow,different traffic flow and acceleration or deceleration of different traffic flows,and explores the statistical distribution law of dynamic amplification factor for simply supported beam under the joint action of the randomness of road roughness and randomness of traffic flow parameters such as vehicle spacing,vehicle weight and vehicle speed,Considering the randomness of road roughness,the difference of dynamic amplification factor between single vehicle and sparse random traffic flow is compared and analyzed.Finally,the statistical analysis value of the dynamic amplification factor of simply supported beam under random traffic flow is explored,and compared with the value of bridge design codes in various countries and regions.The results show that the bridge DAF proposed in the code underestimates the vibration and impact of the actual traffic flow.(4)The dynamic amplification factor of each component of the arch bridge under the action of single vehicle and different traffic density is compared and analyzed.The effects of different distribution characteristics of random traffic flow parameters,such as vehicle spacing in accordance with the lognormal distribution,vehicle weight in the Gaussian Mixture distribution and vehicle speed in the normal distribution,on the fitting distribution of dynamic amplification factor of each component of arch bridge are explored.Under the joint action of the randomness of road roughness and the randomness of traffic flow parameters,the fitting distribution law of dynamic amplification factors at different positions of the arch bridge components is given,the results show that it conforms to the normal distribution,and the value of Chinese bridge design code is less than the upper 95% confidence limit of components.