Fatigue Load Model And Fatigue Bahavior Of Medium&Short Span Concrete Bridges

In the current design and maintenance of bridge structure designers and researchers pay more attention to fatigue problems of steel structures and ignore fatigue behavior of concrete structures. Due to the rapid growth in traffic, carrying capacities of these concrete bridges are degrading over time as well as occurring of fatigue safety problems. As the weak part of mluti-beams concrete bridge, hinge joint suffers from all kinds of diseases more easily under corrosion and fatigue loads.Supported by the technical project of Department of Transportation, this paper surveyed traffic condition of typical national highway and provincial highway in Quzhou Province and deduced standard fatigue load model. Cracking mechanism of prestressed concrete hollow plate girders bridge was investigated. This paper also studied time-varing model of lateral distribution and time-dependent fatigue reliability based on hinge-joined plate method considering shear stiffness of hinge joint. Specific studies and achievements are as follows:1. Fatigue load spectrum and relevant traffic volume were presented based on statistical data of typical national highway and provincial highway in Quzhou Province. Standard fatigue load models of different kinds of roads were deduced according to the principle of fatigue damage equivalence which were highly accurate and suitable and compared with other fatigue load models.2. Based on the standard fatigue load models, numerical analysis of cracking mechanism was conducted from statical behavior and fatigue behavior which shows that statical design load in new code would not lead to deck cracking. The time that fatigue damage of hinge joint leads to deck cracking is rarely short. By the study of influence factors of fatigue, it’s found that larger thickness of pavement and transverse prestress could increase fatigue life of the structure.3. Shear stiffness degradation model of different kinds of hinge joints that suffering from corrosion and fatigue were studied based on the material characteristics degradation model of concrete, steel bars and degradation model of slab-hinge joint bonding stiffness. Numerical analysis of hinge joint shear bearing capacity was conducted. Shear bearing capacity of shallow hinge joint is far less than deep hinge joint. Steel bars in hinge joint have little effect on elastical performance but they could significantly improve shear bearing capacity of hinge joint.4. Using the shear stiffness degradation model of hinge joint, time-dependent deformation of lateral load-distributing influence lines were studied. The results of hinge-joined plate method considering shear stiffness of hinge joint were compared with grillage analytical method and3-D solid finite element model. The results agree well. Furthermore, time-varing model of lateral distribution coefficient was deduced and was applied to the analysis of time-dependent fatigue reliability.