Dynamic Response Analysis And Fatigue Performance Assessment Of Composite Bridges Considering Resonance And Cancellation Effects

With the continuous development of economy and society,the scale of China’s railway network will be further expanded.The railway operation also tends to be "high-speed and large-capacity",which sets higher requirements for railway bridges.Steel-concrete composite bridges,with their unique properties and advantages,have been widely used in western countries such as Europe and the United States,but are rare in China.Therefore,it is of practical significance to study the dynamic response and fatigue performance of steel-concrete composite bridges under moving train load,providing gudielines for the design and maintenance of steel-concrete composite bridges in China.The vertical and torsional resonances and cancellation effects of simple supported beams under the eccentric moving train loads are considered in this paper.Based on vehicle-bridge coupling dynamic model,the dynamic response and fatigue performance of steel-concrete composite bridges are mainly studied.The main conclusions of this dissertation are as follows:(1)Vertical and torsional resonance and cancellation effects of simply supported beams under eccentric moving train loadThe load of eccentric moving train is equivalent to a series of concentrated forces and torques.The analytical solutions for centroid vertical and torsional responses of simply supported beams under single load,equidistant load sequence and whole train load are derived respectively.Starting from the analytic solution,the formulas of vertical and torsional resonance and cancellation speed are given respectively,and their respective mechanisms are illustrated.Numerical examples are given to validate the theoretical derivation.The research shows that the resonance speed is related to the full length of the vehicle and the natural frequency of the bridge;The cancellation speed is related to the axle distance between bogie centers of the vehicle,the wheelbase between the two wheel sets of a bogie,the length and the natural frequency of the bridge.(2)Vehicle-bridge coupling dynamic modelThe vehicle-bridge coupling system is divided into a vehicle sub-model and a bridge sub-model,and the two are coupled together by the wheel-rail contact relationship.The vehicle sub-model is established by multi-rigid body theory,and the bridge sub-model is established by the modal synthesis method.The osculation assumption is used to simulate the relationship between vertical and horizontal wheel-rail contact,and track irregularity excitation is also considered.According to the above theories,the vehicle-bridge coupling dynamic model is established by Matlab programming,and the model verification is carried out by the measured data of high-speed railway bridges.(3)Dynamic response analysis of steel-concrete composite bridgesSelecting a steel-concrete composite bridge of high-speed railway as an example,the effects of train speed on the centroid vertical response,torsional response and eccentric vertical response of the composite bridge are studied based on the vehicle-bridge coupling dynamic model established in this study.The influence of track irregularity and damping ratio on the dynamic response of the composite bridge is also analyzed.The results show that:①the centroid vertical or torsional response of the composite bridge will be magnified when the speed of the train meets the vertical or torsional resonance conditions,and the lower resonance order,the more obvious magnification effect;② the torsional effect has obvious influenced on the eccentric vertical acceleration responses of the composite bridge;③ the track irregularity excitation has an adverse effect on the dynamic response of the composite bridge;④increasing the damping ratio can reduce the dynamic response of the composite bridge.(4)Shear stress analysis of studs in steel-concrete composite bridgesThe calculation method of the stud longitudinal shear stress caused by vertical bending of steel-concrete composite bridge and the stud lateral shear stress caused by torsion of steel-concrete composite bridge are deduced.The effects of torsional effect,section position,train speed,track irregularity and damping ratio on the stud shear stress response of the composite bridge are studied respectively.The results show that:①the torsional effect has little influence on the shear stress of the stud;②the beam-end of the composite bridge is the most unfavorable position for the stud shear resistance;③the stud shear stress increases when the composite bridge resonates;④the track irregularity has an adverse effect on the stud shear stress;⑤increasing the damping ratio can reduce the stud shear stress.(5)Fatigue performance assessment of steel-concrete composite bridgesThe Miner linear cumulative damage theory based on S-N curve is used,the stud is selected as the significant fatigue detail of steel-concrete composite bridge,then the fatigue performance assessment method of the composite bridge considering vehicle-bridge interaction is proposed.The effects of section position,train speed,track irregularity and damping ratio on the stud fatigue behavior of the steel-concrete composite bridge are studied respectively.The research shows that:① the beam-end of the composite bridge is the most unfavorable position for the stud fatigue performance;②the fatigue damage of the stud increases when the composite bridge resonates;③the track irregularity has an adverse effect on the stud fatigue performance;④increasing the damping ratio can reduce the stud fatigue damage.