Mechanical Analysis And Safety Evaluation Of Bridge Damaged Cable

Cables (or slings) are the important parts of cable bridge structure such as long span cable-supported bridges and half-through or through arch bridges. Many accidents show that the cable damage often causes the bridge mechanical characters change, even threaten the bridge safety. Due to the complexity of cable system and the lagging study on damaged cable, there is not a systematic research for cable about mechanism analysis, damage identification, mechanic calculation and safety evaluation of damaged cable. In this paper, theoretical analysis, simulation calculation and bridge example are associated to study some key problems about static calculation, dynamic analysis and safety evaluation of damaged cable system. The main contents are as followings:(1) In order to solve the problems of short cable tension test and calculation, the analysis model of short cable is built on the basis of the reasonable simulation for the boundary conditions of cable, the calculating formula is deduced and solved by Matlab program. The concept of boundary condition coefficients is put forward and the influence factors for boundary conditions of short suspenders are determined. Moreover, YiChang Bridge as an example, the analysis results of three models are compared and analyzed to verify the availability of complex boundary conditions.(2) Based on the finite-element theory and matrix perturbation theory, sling damage is simulated as the 1^st perturbation of sling system, the general tendency of damage suspender tension is analyzed in theory. Meantime, a 3D finite-element model of a concrete-filled steel tube arch bridge is built to research the redistribution factors of cable tension about single and multi-cable damages system, some correlative conclusion is drawn.(3)According to the analysis for the change rates of cable before and after damaged, a quick damage identification method which combined the structure integral frequencies with the local cables tension, is put forward, at the meantime, a quick cable damage positioning method is presented, which the weighted products of the coordinate change rates in Z orientation are taken as the damage identify indicators. And a simulation calculation is carried out to verify their availabilities. (4) The attenuation regularities of wires intension caused by Daniel effect are analyzed, a cable safety evaluation model is built based on safety factors. And the matrix form of limited state function is built to simplify the calculation process by computer, the random samples are generated according to their distributing characters, then the Monte-Carlo method is used to assess the cable safety, then a critical number of broken wires is determined and applied to the rapid assessment of cable safety.(5) According to cable corrosion mechanism and damage evolvement process, the life cycle of corrosion cable is reduced into four stages, which includes jacket ageing stage, zinc coat corrosion stage, steel wire uniform and pitting corrosion stage and fatigue corrosion stage. Based on the research of Faraday and Paris, the time models of four stages are built, the life cycle of corrosion wire and every stage time proportion are analyzed, and the cable corrosion life is evaluated approximately.