Study On The Normal Stress Distribution Characteristic Of The Main Beam Of A Long-span Wide Mixed-beam Cable-stayed Bridge With A Single Tower

In recent decades,with the emergence of finite element analysis,a large number of wide and thin hybrid girder cable-stayed bridges have been successfully applied in engineering practice.However,due to the increase in bridge span,the stress distribution of the beam of hybrid girder cable-stayed bridges during bridge operation has a significant impact on its bearing capacity,and if the stress distribution of the beam is ignored,the safety and economy of the entire bridge structure may be affected.Based on the project of the single-tower hybrid girder cable-stayed bridge(Huaihe Grand Bridge),this thesis conducted theoretical research on the normal stress distribution of the hybrid girder section using the energy variation method.By using FEA solid model and Midas civil truss model,the normal stress distribution pattern of the hybrid girder section under different working conditions was studied,and a method of "effective distribution height" for dealing with the shear lag effect was proposed.The main research contents and conclusions of this thesis are as follows:(1)Theoretical calculations were conducted on the normal stress of the double-ribbed cross-section beam that bears the vertical load,axial force simultaneously,and lateral force.The Poisson’s ratio was introduced to consider the influence of lateral force on the normal stress of the beam section.The normal stress of the edge beam section of the hybrid girder cable-stayed bridge was calculated using the method of dissection,and the theoretical and simulation results of the main sections were compared.The results showed that,when the axial force remains unchanged,the impact of lateral force on the normal stress of the beam depends on the ratio of lateral force to axial force.The impact of lateral force on the normal stress of the beam of the double-cable surface hybrid beam cable-stayed bridge is relatively small,and the theoretical calculation results are consistent with the civil simulation results,thus verifying the theoretical analysis.(2)FEA and Midas civil software were established to analyze the distribution pattern of normal stress in the main beam of a cable-stayed bridge with a dual-pylon and hybrid girder under different bearing capacity limit state conditions.The study found that under the basic condition 3(including overall cooling + gradient heating),the normal stress of the cross-section of edge-span concrete beams was highest,and the maximum value of the beam section appeared at the junction of the web and the roof,and the junction of the small longitudinal beam and the roof.It was recommended to focus on monitoring the above-mentioned concrete beam section positions during the warming period in the winter when the temperature was relatively low.The small longitudinal beam of the roof of the mid-span steel-concrete composite girder had a reducing effect on the normal stress of the roof,while the secondary small longitudinal beam had the opposite effect,and therefore the area of the middle small longitudinal beam could be appropriately increased.Positive and negative shear lag alternation phenomenon was observed in the hybrid girder,and the non-uniformity of normal stress was more pronounced near the web and small longitudinal beam position.(3)According to the distribution of normal stress on the cross-section of a hybrid girder under the most unfavorable load combination,the shear lag coefficient and effective distribution width of the hybrid girder were calculated and analyzed.Additionally,a new method was proposed for dealing with the uneven distribution of normal stress on the beam section by introducing effective distribution height.The research revealed that the longitudinal I-beams on both sides mainly bore the effective distribution width of the mid-span composite girder deck,and the method of considering the shear lag effect with effective distribution height had the same effect as the method of considering effective distribution width on the engineering structure.