The Evaluation And Maintenance Study Of The Existing Steel Box Girder Bridge

With rapid growth of our national economy and high-speed development in highway transportation, both the quality and the quantity of steel products made by our country have been improved greatly. The technology of bridge design and construction also develops entirely. Steel box girder, a traditional and new-pattern bridge type, with light weight, well stability, high anti-torsion stiffness, convenient construction and maintenance, has been widely applied and popularized in highway bridges.The development history of steel box girder bridges in our country has been nearly half a century, which belongs to the middle aged existing bridges. They can hardly adapt to the high-speed development of transportation, especially for the increasing trend of traffic and heavy load, because of aging, damage and lower design grade. There are urgent needs to carry out some researches on the evaluation and maintenance of the existing steel box girder bridges, whose failure mode are fatigue-damage failure under the action of random alternating time-dependent loads. Fatigue and corrosion are two main factors related to the structural behavior and service life.This thesis is to study fatigue failure behavior and fatigue life of existing steel box girder bridges, based on the fatigue-damage accumulation theory. It makes a summarization of the compilation methods and key points of fatigue spectrum by investigating the fatigue load spectrum home and abroad. It makes observation of traffic loads and does statistical analysis to get the characteristics of vehicles for highway bridge. The numerical simulation loading on a 3-dimentional finite-element model is carried out based on Monte-Carlo theory to get related parameters by sampling, such as vehicle type, weight and spacing. Random sampling programs are developed by the mathematical software MATLAB. Rain-flow counting method has also been adopted in another program to get the stress spectrum at critical positions from statistical analysis on random waveform. Afterwards, traditional damage-accumulation theory and deterministic damage-tolerance assessment are respectively used in the decision of the damage conditions and life-span to calculate the intervals of maintenance of steel girder bridge. In the end, anti-corrosion coatings of steel box girder bridges are summarized from the accomplished home and aboard on outer surface, inner surface and deck surface. It is found that to keep the coatings well is important in maintenance of steel box girder bridges.In addition, the methods of the thesis are demonstrated correct and feasible by using the numerical examples of simply supported steel box girder, providing reference for the practical application of the study on evaluation and maintenance of the existing steel box girder bridges.