Research On The Calculation Method Of Impact Factor Of Large Span Continuous Girder Bridge Under Different Traffic Flow State

Large-span continuous girder bridges are widely used in the central and western regions of my country due to their adaptation to the terrain and their beautiful linearity.So far,there have been many studies on the dynamic response of bridges under typical vehicle models,but the dynamic response changes are more complex due to different traffic flow states under natural traffic conditions,but what does not match is that there are relatively few relevant research results for this kind of situation at present.Therefore,it is of great relevance to conduct research in this area.As an important part of the key R&D project of Shanxi Province(No.201803d31076),the paper takes the three-span continuous girder bridge as the background,and investigates the coupling analysis model of the bridge under different traffic flow conditions.The random traffic flow and bridge dynamics models under typical traffic flow patterns in accordance with the bridge design code are established respectively,and the spatial bridge deck roughness model considering the asymmetry of left and right wheels is established,Based on the displacement compatibility equation and mechanical coupling relationship between vehicles and bridges,the vehicle bridge coupling analysis model under different traffic flow conditions is established.The vehicle bridge coupling analysis system is developed with MATLAB software,and Newmark based on time-varying dimension preprocessing is proposed-βIterative solution method;Based on the continuity of bridge dynamic response,a calculation method of bridge impact coefficient based on screening method is proposed,and the dynamic response of bridge under fleet speed and bridge deck roughness is analyzed.The results show that the impact coefficients have an undulating distribution,for the bridge dynamic response and impact coefficients are relatively little affected by the changes in the fleet travel speed,while the impact of bridge deck roughness is relatively large.Under the condition of grade C～D bridge deck,the increase of bridge impact coefficient is large,which exceeds the value of impact coefficient in different countries.It is suggested to increase the impact of bridge deck roughness in the subsequent revision of the code.Through the research on the dynamic response of long-span continuous girder bridges under different traffic flow conditions,this paper can not only provide reference for the calculation of vehicle bridge coupling dynamic response and impact coefficient of such bridges,but also provide technical support for the design,reinforcement,maintenance and operation management of similar bridges.