| With the great spanning capacity and superior economic performance,hybrid-girder cable-stayed bridge has been widely built in long-span highway,and has gradually become the preferred bridge type for long-span railway bridges.Due to the heavy railway load and obvious live load effect of railway bridges,it is necessary to study the fatigue performance of steel-concrete joint section.The fatigue properties of the steel-concrete joint section was stuied based on example of the Bianyuzhou Yangtze River Bridge on the Anqing-Jiujiang Railway with a main span of 672 m.The main research contents and conclusions are as follows:(1)This application and development of hybrid girder cable-stayed bridge are recalled.Research progress on fatigue performance of the steel-concrete joint section of hybrid-girder cable-stayed bridges is reviewed.(2)For regular codes both at home and abroad,the classification of the fatigue details of the steel structure is introduced.The basic theory and scope of application of the nominal stress method and the hot spot stress method are explained.(3)Based on the team’s research results on the mechanical properties of railway of the steel-concrete joint section,the structural and mechanical characteristics of two types of the steel-concrete joint section were compared and analysed.and,the fatigue performance of the short steel-concrete joint section of the Bianyuzhou Yangtze River Bridge was proposed by the finite element analysis method.(4)Starting with the fatigue-prone details of actual bridge steel-concrete joint section,according to the principle of equivalence and the Saint-Venant principle,considering the design traffic density the model test of the steel-concrete joint section was designed and carried out.The scale of the model is 1:2.Based on resuls of the 2.15 million fatigue model test of the steel-concrete joint section,the fatigue performance of the steel-concrete joint section was analyzed,and the bond-slip failure mechanism of the steel-concrete interface and stiffness change laws were discussed.The results revealed that: the overall stress level of the steel-concrete joint section is lower during the design service life,stress at key measuring points maintain almost constant along with the fatigue.The steel-concrete joint section has good fatigue performance.The fatigue performance of the steel-concrete joint section is better than other section.When designing the steel-concrete joint section,avoid the stress concentration occurs at regions with abrupt geometrical changes;Cracks will initiate at low cycles,and the steel-concrete interface will be completely separated at 33% of the design service life.(5)Based on fatigue test results and the nonlinear theoretical model,the fatigue performance of the steel-concrete joint section is evaluated by the nominal stress method and the hot spot stress method.Based on Miner’s fatigue damage theory,the fatigue life of the steel-concrete joint section under the existing traffic volume is calculated,the effect caused by the finite element model simulation details on the fatigue stress amplitude of the steel-concrete joint section is researched,Finally,with the help of the finite element model of the nonlinear theoretical model,based on the principle of control variables,the reasonable value of the structural parameters that have a greater impact on the fatigue performance of the steel-concrete joint section are discussed.The results show that the fatigue strength of the weld of the web and the stifening rib web is greater than that of the category 100 in the Eurocode3.And the fatigue life of the steel-concrete joint section larger than 118-year;when using the hot spot stress method to evaluate the steel-concrete joint section,it is recommended that the mesh size be 2 mm～4 mm;Combin39 nonlinear spring element was used to simulate shear connector;and the bonding force between steel plate and concrete can be ignored.the hot spot stress of weld of the steel-concrete joint section should be calculated by the IIW quadratic method;as the diameter of the stud increases,the fatigue stress amplitude of the steel top plate and the shear connector decreases with quadratic function,hence,the diameter of the shear stud recommended for the actual design should not be less than 19 mm;the thickness change of the bearing plate only has a significant effect on the fatigue stress amplitude of the bearing plate,and its thickness should not be no less than 30mm. |
