Research On Dynamic Performance Of Continuous Rigid Frame Bridge With Constant Cross Section And Low Pier

In this paper,taking three spans prestressed concrete continuous rigid frame bridge of Nanchang Hongdu Avenue expressway reconstruction project as the research object to study the influence of heavy vehicles with different axle numbers on the vibration response of the bridge.The vibration equations of vehicle models with different axle numbers were derived,and the bridge finite element models were established by Midas and ANSYS respectively to analyze the dynamic characteristics of the bridge.Based on the vehicle-bridge coupled vibrational theory,the vehicle-bridge coupled vibration equations under single vehicle and multi vehicle loads were established.The traditional Newmark-β numerical integration method was used to solve the vehicle induced vibration response of the bridge,and analyzed the effect of dynamic performance of continuous rigid frame bridge.The main work and conclusions of this paper are as follows:(1)Based on D’Alembert principle and virtual displacement principle,the vibration equations of 2-axle,3-axle,4-axle rigid truck and 3-axle,4-axle,5-axle,6-axle semi-trailer truck on expressway were derived.The vehicle-bridge coupled vibration programs of different vehicle types were compiled by MATLAB software,and the accuracy and applicability of the vehicle bridge coupled program was verified by ANSYS transient analysis.(2)Using ANSYS and Midas/Civil finite element software,the ANSYS solid finite element model and Midas/Civil grillage finite element model of the bridge were established respectively.Changing the bridge structure system,pier height and side to middle span ratio to analyzed the influence of bridge structure parameters on dynamic characteristics.The results show that: the first order vibration mode of continuous rigid frame bridge is the longitudinal displacement of pier and girder;the first order vibration mode of continuous beam bridge is the vertical bending of girder,it is the same as the vertical bending mode of continuous rigid frame bridge,which has the same section type and span,and the frequency difference is 1.3%.The change of pier height has great influence on the mode which is dominated by the pier.The middle span ratio of girder has great influence on the vertical bending and torsional modes of girder.(3)Taking a three-axle truck as the analysis object,the influence of bridge structural parameters(including bridge structure system,pier height,bridge side to mid span ratio and deck irregularity)on the dynamic response of continuous rigid frame bridge was studied.The results show that: the dynamic response rule of the continuous rigid frame bridge is similar to that of the continuous beam bridge,and the mid-span response of the side span is greater than the mid-span response.The closer the vehicle is to the center line of the bridge,the greater the dynamic response of the bridge is.The longitudinal displacement of the bridge increases with the increase of pier height.Changing the height of piers has great influence on the mid-span deflection and little effect on the mid-span bending moment.The change of pier height has a great effect on the negative bending moment at the pier top,and the negative bending moment decreases with the increase of pier height.With the decrease of side-to-span ratio,the negative bending moment of pier-top girder increases,and the mid-span deflection decreases,but the mid-span bending moment changes little.(4)With the same vehicle weight,the more number of vehicle axles,the smaller dynamic response of bridge.When the axle number and weight of the vehicle are the same,the dynamic response of the bridge caused by the trailer is greater than that of the rigid truck.The greater weight of vehicle,the greater the dynamic response of the bridge,but the impact effect of the bridge is smaller.When the vehicle wheelbase and vehicle speed meet a certain relationship,the impact coefficient of the bridge reaches the peak,but for small and medium span bridges,the vehicle action time is short,and the vibration energy transferred to the bridge is limited.For the vehicle with smaller wheelbase,it is easier to cause greater impact effect on the bridge.(5)Under the action of multiple vehicles,the impact coefficient decreases with the increase of the number of transverse vehicles.With the increase of the longitudinal vehicle spacing,the impact coefficient is closer to the single vehicle condition.