Research On Vehicle Load In Special Lanes For Freight Cars On Highway Bridges Based On "Passenger And Freight Separation"

As the most basic and important variable load in highway bridge design,automobile load has an important impact on the safety and durability of highway bridges.At present,highway transportation of China still adopts the operation mode of mixed passenger and freight.With the rapid development of China’s economy,the characteristics of highway traffic flow are also changing.The efficiency of passenger cars is decreased by the increase of the proportion of trucks and the relatively low speed of trucks,and safety acc idents are caused by the mixed traffic of passenger and freight,so the normal operation of the bridge structure is seriously threatened.In order to effectively alleviate the potential safety hazards of the mixed flow of passenger and freight and improve operation efficiency,the "passenger and freight separation" operation mode will be an effective way,which means that passenger cars and trucks are driven separately,and a dedicated truck lane for trucks is established.Aiming at the operation mode of "passenger and cargo separation",this paper studies and explores the adaptability of automobile loads in China’s current general code for design of highway bridges and culverts.The main research contents and results are as follows:(1)The Chinese General Code for Design of Highway Bridges and Culverts was compared with the car load standards in the relevant codes of the United States,Britain,Canada,Japan,and Europe.Through the analysis of the load effect,the standard value of the car load in the Chinese code was obtained.In terms of safety,the conclusion was that it was at the upper-middle level in the world.(2)Through the analysis of the vehicle composition and vehicle weight of the 12 lanes,it was concluded that the proportion of six-axle vehicles in the four lanes accounted for more than 50%of the total number of vehicles in the lane,and the number of vehicles over 49 tons accounted for the total number of vehicles in the lane.According to this,the traffic characteristic data of these four typical freight lanes were selected as sample data to analyze the vehicle load characteristics of truck lanes.(3)Through the statistical analysis of the four selected mixed passenger and freight lanes,the total vehicle and cargo weight,axle load,wheelbase,and headway time,it is obtained that the total vehicle and cargo weight,headway time and axle weight distribution ratio basically obeyed with the conclusion of normal distribution or lognormal distribution,various statistical characteristics of the vehicle load flow on the four lanes were obtained.(4)Taking the continuous truck fleet information on the four mixed passenger and freight lanes as the load flow samples of the truck lanes,and taking the six-axle truck as the representative truck model,statistical analysis showed that the total weight of trucks and cargo and the headway time basically obeyed the normal distribution or the statistical law of lognormal distribution,as well as the various statistical characteristics of the load flow of the continuous truck fleet,and a random load flow that obeyed its distribution was generated by the Monte Carlo method.(5)In order to analyze the statistical characteristics of the continuous truck flow more systematically,the total vehicle and cargo weight and headway data of other vehicle types except for six-axle vehicles on the four mixed passenger and freight lanes were eliminated,and the EM algorithm was used to fill the corresponding position vacancies According to the data,the statistical law of the total weight of trucks and cargo,the headway time basically obeyed the normal distribution,and the statistical characteristics of the truck load flow filled by the EM algorithm,and a random load flow that obeyed its distribution was used by the Monte Carlo method to generate.(6)Taking simple-supported beams and third-equal-span continuous beams as typical bridge samples,the load flows processed by different methods were respectively applied to the main control section internal force influence lines of typical bridge samples with different spans,and the generated control sections were calculated It was compared with the calculated effect value of the vehicle load specified in the code,and the conclusion was drawn:The mid-span bending moment effect of the simply supported beam and the fulcrum shear effect generally did not exceed the effect of the vehicle load specified in the code;the mid-span bending moment effect of the continuous beam and the mid-span mid-span bending moment effect did not exceed the code requirements in general The effect of the automobile load;the bending moment effect of the support section of the continuous beam exceeded the effect of the automobile load specified in the code.Therefore,in order to ensure the safety and durability of the bridge,it was recommended to appropriately increase the vehicle load standard for truck lanes on the basis of the current normative value standard.