| Since the Ministry of Transportation vigorously promoted the steel bridge structure in2016,the steel-concrete composite girder bridges have been developed rapidly in highway construction in China.However,the impact factor characterizing the dynamic effect of traveling vehicle is lack of sufficient research for this type of bridge.The calculation formula of impact factor in the current code is based on the actual measurement of reinforced concrete girder bridges,and it is not clear whether it is applicable to steel-concrete composite girder bridges.Based on this,the vehicle-bridge coupling vibration analysis model is established by ABAQUS finite element model on the basis of a detailed investigation of the regulations regarding impact factors in the domestic and foreign codes and the collection of a large number of the vehicle-running test datas of bridges.After the model is validated by the previous calculation examples and bridge field test,the impact factors of steel-concrete composite girder bridges are studied based on numerical methods,including the steel-concrete composite box girder bridge,the steel-concrete I-shaped composite girder bridge,the prestressed concrete small box girder bridge and the prestressed concrete T-shaped girder bridge.The main research findings are as follows:(1)The regulations regarding impact factors in the bridge design codes of 13 countries or regions such as China,the United States,Canada and Japan are summarized.To date,there is no consensus on the value of the impact factor among countries,and the value of the impact factor varies greatly.(2)This thesis collectes the tested impact factors of 106 bridges,including simply-supported girder bridges,continuous girder bridges,continuous rigid frame bridges,arch bridges,suspension bridges and cable-stayed bridges.For simply-supported girder bridges and continuous girder bridges,when the fundamental frequencies of the bridges are less than 4.0 Hz,the situation that the values of impact factors in current code are less than the tested values often occurs,especially for continuous girder bridges.(3)Four 40 m simply supported girder bridges and four 3×40 m continuous girder bridges,whose design loads are all highway Class I and whose deck widths are similar and range from 12 m to 13 m,are taken as examples.The impact factors of steel-concrete composite girder bridges and prestressed concrete girder bridges under different bridge surface roughness and vehicle speeds are compared.The results show that prestressed concrete T-shaped girder bridge has a large impact factor,while the impact factors of steel-concrete composite box girder bridge,the steel-concrete I-shaped composite girder bridge and the prestressed concrete small box girder bridge are relatively consistent.(4)When the grade of bridge surface roughness is Grade A,the current code in China can be used to calculate the impact factors of steel-concrete composite continuous box girder bridges and steel-concrete I-shaped composite continuous girder bridges.For steel-concrete composite simply-supported girder bridges,the impact factors suggested in the code are available in the sense of average velocity.When the grade of bridge surface roughness is Grade B and Grade C,the calculated values of the impact factors exceed the standard values by more than 100%,and the values of the impact factors in the current Chinese code are unreliable.(5)The effect of vehicle speed on impact factor is complicated.The variation curves of impact factors of simply-supported girder bridges fluctuate and rise with the increase of vehicle speed,and the peak values of the impact factors are obtained at the maximum speed.Impact factors of continuous girder bridges show a fluctuating upward trend overall,and the large impact factors can be generated when the vehicle runs at high speed.When the grade of bridge surface roughness decreases,the impact factors increase sharply.The amplifications of the impact factors increase with the decrease of the grade of bridge surface roughness. |
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