Study On Coupled Vibration And Lateral Stiffness Of Steel Girder Cable-stayed Long-span Road-rail Bridge

The large-span road-rail bridge is beautiful in appearance,and the characteristics of "one bridge with dual-purpose" is to give full play to the economy and environmental protection.However,at present,there are few researches on vehicle and train load combination,lateral stiffness and random traffic flow of road-rail cable-stayed bridge with main span over 600 meters.Therefore,in-depth research on vehicle-bridge coupling vibration and lateral stiffness of road-rail cable-stayed bridge can provide reference for the subsequent design of similar projects,which has great engineering significance.Based on the engineering background of a combined road-rail bridge with the largest span in the world,this thesis conducts a systematic study on vehicle-bridge coupling vibration and bridge lateral stiffness.The main contents and conclusions are as follows:(1)According to the characteristics of wide deck and large main span of the bridge,the influences of lane location,vehicle speed,vehicle weight,vehicle distance,number of carriages,steel girder stiffness and pylon stiffness on the transverse stiffness and vehicle-bridge coupling vibration of the bridge were comprehensively analyzed.The following laws were obtained: 1)The closer the lane is to the flange plate of the bridge,the greater the influence of partial load will be.2)The lateral stiffness of the bridge can be effectively improved by appropriately limiting the car weight,train weight and the number of train cars.3)As the stiffness of the main beam and pylon increases,the deformation ability of the bridge decreases.For this bridge,when the stiffness coefficient of the main beam and pylon is set between 0.9 and 1.1,the bridge has good economy and safety.(2)In this thesis,the mid-span section is selected as the research section,and a more reasonable combination method is adopted to carry out the combined load of cars and trains.The results show that the most unfavorable load combination of the bridge is the load combination of the whole lane.In the case of the most unfavorable load,the transverse displacement and acceleration of the bridge,the acceleration of the vehicle,the lateral force of the wheel axle,the derailment coefficient and the load reduction rate of the wheel weight are all within the range specified in the code,which indicates that the safety of the bridge,the safety of the vehicle and the comfort of the passengers can be guaranteed.(3)By reducing the transverse stiffness of the bridge and taking the evaluation criteria of vehicle safety and passenger comfort stipulated by the code as the limits,this thesis studies the transverse stiffness limits applicable to long-span road-rail bridges.The results show that when the transverse deflection span ratio of the bridge is less than1/2400 and the transverse displacement of the pier top is less than 30 mm,the safety of the vehicle and the comfort of passengers can still be ensured.When the vehicle-bridge coupling vibration is studied on a long-span road-rail cable-stayed bridge with a speed limit of 72km/h for vehicles and 120km/h for trains,the recommended value of the transverse deflection span ratio is 1/2400 and the recommended value of the lateral displacement of the pier top is 30 mm.(4)This bridge adopts large sample size to study the regularity of bridge transverse dynamic response under the action of random traffic flow.The research shows that the bridge transverse dynamic response under the action of random traffic flow basically conforms to the normal distribution.Therefore,the theoretical maximum of the transverse dynamic response of the bridge under the action of random traffic flow is obtained,and the transverse dynamic response of the bridge under the action of non-random traffic flow is compared,and the rate of change is obtained.Considering the relationship between transverse dynamic response,bridge width and bridge structural system,this thesis takes the bridge width and structural system as variables,and calculates the correlation between the change rate and the lateral width of the bridge under different structural systems,and proposes the transverse dynamic response coefficient of the road-rail cable-stayed bridge with the main span less than 660 meters and the bridge width less than 38 meters under the action of random traffic flow.