| The rapid development of long-span bridges in China has made continuous breakthroughs in span and quantity.Ensuring the safe service of bridges is a major demand for the healthy development of the national economy and society.As the key bearing part of long span bridge,the suspender is prone to corrosion in unfavorable environment.The suspender is composed of protective measures,suspender body and anchoring system,which is in a high stress state for a long time.With the increase of traffic volume and vehicle axle load,corrosion fatigue damage is gradually becoming the main reason affecting the service safety of bridge.In this paper,according to the practical requirements of safety assessment of suspenders with high corrosion disease,the corrosion fatigue damage mechanism of suspenders is revealed,the corrosion fatigue failure criterion of suspenders is constructed,and the multi-scale analysis method of corrosion fatigue of cables of long-span bridges is proposed.The main research works are as follows:(1)The static and fatigue properties of high-strength steel wires with different damages were tested.The influence of corrosion pit morphology on steel wire properties was revealed,the relationship between notch size and fatigue life of steel wire specimens was clarified,and the function expression of notch morphology-length ratio and life was established.The detailed three-dimensional solid numerical model of the damaged steel wire was constructed,and the stress distribution characteristics of stress concentration near the notch root were defined.The shape factor and conversion factor were introduced to characterize the stress concentration coefficients of different notch types,and the critical distance of the notch root was determined based on the local stress gradient near the notch.The fatigue life prediction model of notched steel wire considering the mean stress amplitude and critical distance is proposed.The fatigue life prediction method based on critical region method is verified by the fatigue life test results of notched steel wire.(2)The life evaluation method of corroded steel wire based on equivalent initial crack size is presented.The effect of corrosion rate and stress ratio on fatigue life of high strength steel wire was investigated.The three-dimensional contour model of corroded steel wire based on three-dimensional scanning technology was constructed,and the relationship between the maximum pit depth of corroded steel wire and corrosion rate was clarified.The numerical model of corroded steel wire was established,and the quantitative relationship between stress concentration factor and corrosion rate was revealed.The stress concentration caused by corrosion pits was introduced into the stress intensity factor model.Based on the principle of equivalent initial crack size,the fatigue life prediction model of corrosion steel wire was proposed considering the corrosion growth stage and fatigue crack growth stage,which provided a new idea for corrosion fatigue life evaluation of suspender steel wire.(3)A numerical simulation method of steel wire fatigue crack propagation based on linear fracture mechanics theory is presented.The fatigue crack growth tests of steel wires under different stress ratios were carried out.The strip fracture morphology was obtained by the stepby-step fatigue loading method,and the effect of the stress ratio on the crack growth rate was clarified.The crack growth fatigue cycle number curve under different stress ratios was established,and the change rule of the fatigue crack growth model parameters with the stress ratio was revealed.Based on SEM analysis,the fatigue fracture mechanism of steel wire is clarified,and the critical fracture characterization parameters required for numerical simulation are statistically analyzed.Combined with ABAQUS and FRANC3D,a numerical model of fatigue crack growth was established.The numerical model was verified by the experimental data of this study and the open literature.The parameter sensitivity analysis of the numerical model was carried out,and the influence of various parameter factors on the fatigue life prediction of corroded steel wire was discussed.(4)A Bayesian network updating method for steel wire fatigue crack propagation evaluation was proposed.The corrosion fatigue crack growth test of suspender steel wire under different stress ratios was carried out,and the prior probability distribution of fatigue crack growth rate model parameters was obtained.ABAQUS and FRANC3D software were combined to simulate the crack growth of steel wire.The fatigue crack growth model of suspender steel wire induced by local corrosion is developed.Bayesian network is used to infer and characterize the uncertainty of the parameters of the corrosion fatigue coupling model.Markov Monte Carlo simulation is used for posterior inference to update the model parameters.Combined with the corrosion fatigue test parameters and numerical simulation results of suspender steel wire,the proposed probabilistic fatigue damage assessment framework is verified and analyzed.(5)A multi-scale evaluation method for corrosion fatigue of bridge suspender was proposed.The influence of parameters such as initial crack size,fatigue crack growth threshold,fatigue crack growth parameters and fracture toughness on steel wire life was revealed,and the distribution law of each parameter was clarified.The Weibull distribution model of steel wire fatigue life based on probabilistic fracture mechanics was established,and the influence of corrosion on the model parameters was discussed.Based on the fiber bundle theory,the wiresuspender system is regarded as a series-parallel model,and the probability distribution of suspender under different corrosion rates is calculated by using the P-S-N curve equivalent damage path simulation method.Then the parameters of the model were analyzed to clarify the influence of various influencing factors on the fatigue life prediction of corroded suspenders,and the P-S-N curve of suspenders under different corrosion rates was established. |
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