Research on the Long-Term Degradation Mechanism of the Stability Capacity of U-Rib Stiffened Plates in Offshore Steel Box Girders

The steel box girder structure of the offshore bridge is subject to the coupling effect of marine corrosion and vehicle cyclic load at the same time， and in the long-term service process， both seawater corrosion or wheel load-induced deformations， it will have a certain impact on the stability capacity of the U-rib stiffened. In order to study the mechanism of the degradation of the stability capacity of the U-rib stiffened plate of the cross-sea steel box girder during long-term operation， this paper takes the compressive U-rib stiffener member of the steel box girder roof as the research object， and used the ABAQUS finite element software to establish the finite element model of the U-rib stiffened plate to analyze the influence of the coupling effect of the bending deformation and wheel loads of the member in the corrosive environment on the stability capacity of the U-rib stiffened plate. The results showed that for the U-rib stiffened plate with different wheel load ratios， the bearing capacity gradually decreased with the increase of load ratios in the same corrosion period， and the maximum reduction was 5.27%. Under the same overload ratio， with the increase of corrosion duration， the bearing capacity was reduced， and when the overload ratio with the largest degree of reduction was 4， the corrosion duration wad 100 years， which was 9.12% lower than that of the same overload size and non-corroded components， and the size of the wheel load and the corrosion effect of seawater had a certain impact on the stability capacity of the U-rib stiffened plate. In the operation process of the bridge， due to the effect of the structural dead weight and the wheel load， the bridge deck showed different degrees of plastic deformation， so that the force of the U-rib member is no longer a complete axial compressive force， but an eccentric force， when the bending amplitude was L/500， L/250， the ultimate stability capacity of the component was reduced by 9.03% and 19.16% respectively compared with the bending member with the amplitude of L/1000 The increase of bending amplitude reduced the ultimate stability capacity of the component， thereby accelerating the process of reaching the stability capacity of the component， but did not change the failure mode of the component. When the operation time reached 100 years， the ultimate stability capacity of the component considering the coupling action of corrosion loads and deformations decreased by 18.65% compared to its inital states（0 h）. Under the same circumstances， the ultimate stability capacity considering only corrosion and the coupling action of corrosion and load decreased by 8.75% and 8.65%， respectively. The influence of deformations caused by single or coupled wheel loads and dead weight on the stability of U-rib stiffened plate members was more significant than corrosion effects.