| When running the bridge,the high-speed train will cause the vibration of the bridge,and the vibration of the bridge may affect the vibration of the train,the interaction problem called vehiclebridge coupling vibration problem.When the vehicle runs on the bridge,the vehicle not only causes the vibration of the bridge structure,but also this dynamic effect can increase the load effect of the train on the bridge,and intensify the damage to the bridge structure,and this vibration problem increases with the increase of the speed.In recent years,with the large-scale construction of highspeed railways,large-span bridges have been widely used,so the vibration problem of the bridge becomes increasingly important when the high-speed train run across the bridge.The mechanical properties of Extradosed Cable-stayed Bridge(ECSB)are between the continuous girder bridge(continuous girder rigid frame bridge)and the ordinary cable-stayed bridge,The cable of the ECSB is similar to the external prestressing force of the prestressed concrete,which can greatly reduce the stress amplitude of the cable,at the same time,the vertical component of the cable can balance the load caused by the self weight of the beam,so as to reduce the height of the main beam,the horizontal component can better offset the tension caused by the negative bending moment of the main beam near the bridge tower,and ECSB has good aesthetic effect.In recent years,the ECSB has been used in the bridge engineering of high-speed railway,intercity rail and other lines.Within 160-300 m span,the railway ECSB with prestressed concrete have a strong competitive advantage.Therefore,it's of practical significance to study the mechanical behavior of the railway ECSB under vehicle induced vibration.Based on the vehicle-bridge coupling vibration theory and structural finite element theory,the dynamic model that can analyze the internal force behavior of the bridge structure under vehicle-induced vibration was established,the following research works of ECSB were conducted:(1)In order to quantitatively describe the internal force of the ECSB when the vehicle passes through the ECSB,the concepts of bending moment live load ratio,shearing force live load ratio and cable force live load ratio were proposed.The live load ratios of bending moment,shearing force and cable force were about 10%,3% and 1% when the EMU pass the ECSB,respectively,and about 30%,10% and 3% when using ZK load.Based on the established vehicle-bridge coupling analysis model that can analyze the internal force of the bridge,the internal force changes of ECSB of the Rigid Frame System(RFS),Fixed System between pylon and girder(FS),and Supportting System(SS)when the EMU passes through,the results show that compared with the RFS,The maximum displacement of the beam of the FS and the SS increases by 151.35% and 118.57%,the maximum shearing force increases by 9.82% and-15.23%,and the bending moment increases by 73.16% and 58.75%,respectively.The overall mechanical performance of the RFS was better than the FS and the SS.(2)In order to study the Impact Factor spectrum(IFs)of railway ECSB,a railway ECSB of 180m-long was used as an example to establish a vehicle-bridge coupling analysis model.The results show that at the same position of the grider,the shearing force IF > bending moment IF and bending moment IF > displacement IF.Taking four railway ECSBs as examples,the hypothesis testing theory in mathematical statistics and probability distribution was introduced,through statistical analysis,the IF of railway ECSB follows estremvalue type one distribution.The IF of the internationally accepted method with a confidence of 0.05 was used as the IF of the bridge,through regression analysis,the IFs based on the fundamental frequency,span,and speed of the girder displacement,positive bending moment,negative bending moment,and shearing force of railway ECSB were obtained,respectively,the IFs was compared with the measured displacement IF of a ECSB,the results show that the absolute errors of the displacement impact factors respect to fundamental frequency,span and speed were 6.94%,0.43% and 4.59% respectively compared with the mesaured values.The IF of span was closer to the measured value.In order to comprehensively consider the impact of the fundamental frequency,span,speed and other factors on the IF,a formula of railway ECSB IFs that can considering fundamental,span,speed and track irregularity at so on factors was established,A railway ECSB example of 288m-long was analyzed,and the final IFs was 1+?=0.5v/(7.2fL)+ 1.01,which was compared with the calculated value of the existing specifications.The results show the formula could well calculate the displacement IF,shearing force IF and bending moment IF.(3)In order to study the influence of the stay cables on the girder of ECSB,the effect of the stay cables on the internal force and IF of the grider was studied with multiple ECSBs as examples.The result show that the displacement,bending moment,and shearing force of grider decreased by 61.01%,24.51%,and 51.84%,but the stay cables did not change the law of grider IF with speed.Cable breaking as a special load,the breaking of any cable can increase the bending moment,shearing force of the grider,and other cable forces of the stay cables by a maximum of 0.26%,0.26%,11.29%,and the effect of IF of the cable breaking on the grider was relatively small.The overall rigidity of the railway ECSB was controlled by the grider itself.(4)In order to study the difference between railway ECSBs and ordinary cable-stayed bridges,two distinction methods based on Displacement Response Effect Ratio(DRER)and Cable/Grider Live Load Ratio(CGLLR)of cable-stayed bridge from vehicle-induced vibration were proposed respectively.The results show the maximum DRER of railway ECSB was 0.62,that is,if the DRER of railway cable-stayed bridge is less than 0.62,the bridge will is considered to be ECSB;when the main span of the ECSB is about 200 m,the CGLLR of cable-stayed bridge is less than 0.5,that is,if the CGLLR of railway cable-stayed bridge is less than 0.5,the bridge will is considered to be ESCB.The CGLLR is less than 2 for a pan of about 300 m,that is,if the CGLLR of railway cable-stayed bridge is less than 2,the bridge will is considere to be ESCB.(5)In order to study the influence of design parameters on the internal force of ESCB,taking the largest span railway ESCB with concrete girder as an example,the influence of ratio of side to main span,height to span ratio of bridge pylon,height to span ratio of main beam section,cable section area,bending rigidity of bridge pylon,bending rigidity of bridge pier on the mechanical properties of key parts of ESCB and cable/grider live load ratio.The results show that the height of bridge pylon,cable area and main briger height has great influence on the mechanical properties of key parts and cable/grider live load ratio. |
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