Study On The Mechanical Behaviour And Structure Optimization Of Steel Box Girder Deck Pavement

With the rapid development of the long-span bridges construction, steel box girders based on the orthotropic slab become more and more popular, which made the pavement on the steel box girder become one of the key point for the bridge construction. Many researches, which have got some achievements, are based on the mechanical analysis of the pavement in and out of China. However our country's traffic conditions are very complicated, for overloaded and oversize vehicles are very common for the transportation, which results in the effect that even expensive epoxy asphalt can not make the steel bridge pavement reach its life span. It can be concluded that the pavement material improvement is not likely to be broken through. Moreover, structure designs of steel box girder are mostly considered for the structural safety, and designs for the optimizing of the pavement's loading are very scarce, which encouraged new model and design method for the pavement design of the steel box girders.Aimed at the current pavement design situation for the steel box girder, this paper proposed a new pavement design method for the steel box girder based on reducing the dangerous loading condition by improving the box structure. Firstly, by fully and systematically investigation of the effects of key elements of the box structure on the stresses in pavement and the analysis of the economy, we recommend a new method to improve the loading condition of the pavement by the modification of the box structure, and furtherly we study the new integrative design of the pavement and the box girder, besides, some experiemtns and actual engineering tests were carried out. The details of research works are as following,(1) A three-dimensional finite element model for the steel box girder pavement system has been established based on the shell-entity elements to find out the most dangerous loading positon which led to the destruction of the pavement. The mechanical response indexes are studied by parameters of pavement deck, steel box girder, loading conditions, temperatures, and a neat and feasible empirical formula is derived for the maximum transverse tension strain. From the economic analysis for the improvement of the pavement, a new design method is required.(2) Compared to the researches which focused on the mechanical behaviors of the pavement, this paper considered the box girder and the pavement structure as aintegrative system, and proposed a method to improve the loading conditions of the pavement, which focused on improving the roof's rigidity of the box girder by optimizing the box structures. Two methods are recommended respectively for the new bridge and the old bridge reinforcement. The method has been verified in the Pearl River Huangpu Bridge by adding small stiffening ribs at the roofs of the box girder. Moreover, a neat and feasible empirical formula is derived for the maximum transverse tension strain of this new structure.(3) Based on the three-dimensional finite element model with fishbone beam model, this paper used FEM software ANSYS to analyze the mechanical behavior of the wholes bridges, and analyzed the mechanical response of the pavement system by considering the internal forces in a bridge. We set up pavement-girder integrative local models by applying the internal forces as boundary conditions on the local models to study the mechanics responses under multiple combined loads. The analysis results are compared with these by orthotropic slab models, which shows that orthotropic slab models can reflect the mechanics behaviors approximately though the shear stresses and longitudinal tensile stresses have obvious differences. The analysis of pavement-girder integrative local models of the cable-stayed bridge and the suspension bridge also derive that the internal stresses in the pavements of the two bridges have significant different distributions, it means that it is not appropriate to analyze the two pavement stresses by the orthotropic slab models uniformly.(4) A new design method of accelerated loading test on reduced scale for the pavement material is proposed for the better meeting the engineering stress states, which helps to the choose the more duitable pavement material in the engineering.