| In long-span steel or concrete-steel cable-stayed bridges, anchorages between cable and steel girder are key mechanical parts. And there are many types, of which tensile anchor plate is being widely used because of its outstanding advantages, such as simple in structure, convenient to install and maintain, clear in force-transfer, etc. However, its complicated weld distribution and severe stress concentration lead to fatigue problem under traffic loads. In this dissertation, tensile anchor plate of Wujiang Bridge is taken for example, and theories of fracture mechanics, finite element analysis and structural reliability are comprehensively used to establish assessment of fatigue life for anchor plate based on fracture mechanics, providing an effective method for anchor plate s fatigue life assessment.Specific research works in this dissertation are described as follows:(1)Research status of fatigue problem in steel bridges is expounded. Research history and current fatigue design methods are summarized; the basic anti-fatigue design flow is presented; application situation and research status of tensile anchor plate are presented, in addition, its structural and loading features are analyzed, based on which typical fatigue structural details are identified.(2)Research in fracture mechanics is carried out. Calculation methods of stress intensity factor are studied, then analytical and finite element methods are applied to calculated stress intensity factors in typical fatigue structural details, and their variation trends are analyzed.(3)Research in assessment of fatigue life for anchor plates based on fracture mechanics is carried out. First, the whole bridge finite element model of Wujiang Bridge is built, according to which the representative anchor plate is determined; Then fatigue load models in the new standards are loaded according to the cable force influence line, obtaining the fatigue load spectrum; finite element model is combined to obtain the stress pulse of each typical fatigue structural detail; Finally, integral of Paris formula in fatigue crack growth model is calculated to obtain fatigue life.(4) Research in fatigue reliability is carried out. According to fatigue reliability theory, reliability model based on fracture mechanics is established, then distribution characteristics of the basic random variables and the reasonable value of the target reliability index is discussed,which is applied to obtain the curve between anchor plate s fatigue life and reliability index. |
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