| With the rapid development of transportation infrastructure,steel bridges are an important development direction of bridge engineering in my country.However,under the influence of external harsh factors,problems such as fatigue and corrosionof steel bridges are prominent,which seriously affect structural safety and significantly increase structural maintenance and repair costs.The corrosion resistance and economy of weathering steel determine that weathering steel is a viable steel material.But because its carbon content is slightly higher than that of ordinary steel and its welding performance is poor,which will result in relatively serious welding defects and low welding quality and poor fatigue performance.During the actual service of the bridge,the vehicle fatigue load and impact load will reduce the combination of the rust layer and the matrix and even cause the rust layer to expand,crack and fall off,which will result in the continued corrosion of the steel matrix that should be protected.The lower flange of the weathering steel beam usually bears a large reciprocating tensile stress,and the welded joint is affected by welding defects,residual stress and stress concentration.The unfavorable shading conditions of this part further increase the corrosion rate,making the welded joint of the lower flange a sensitive area for corrosion fatigue.Aiming at the key scientific issues such as fatigue performance deterioration and structural safety service faced by weathering steel bridges during service,this thesis takes the weathering steel welded joints as the research object based on the existing research results and literature and clarifies the fatigue performance deterioration mechanism of weathering steel bridges and quantify the effect of corrosion fatigue degradation over time on welded weathering steels.The main contents include:(1)The development status of weathering steel bridges at home and abroad have been investigated,the research direction was clarified,The research status of corrosion process simulation and corrosion fatigue life assessment research methods are introduced.(2)The basic theory of continuous damage mechanics,fatigue damage evolution model and the process of corrosion fatigue life evaluation of weathering steel welded joints are introduced briefly.(3)Based on the atmospheric corrosion process and mechanism of weathering steel,a three-dimensional cellular automaton evolution model of weathering steel welded joints is established,which can accurately reproduce and predict the corrosion evolution process of weathering steel welded joints.The model simulation results show that it conforms to the law of corrosion kinetics,the simulated corrosion morphology shows typical corrosion pit characteristics,and the depth distribution of corrosion pits is weibull distribution.(4)The loading process of the actual fatigue cyclic load is simulated based on the cyclic block loading method,and the corrosion evolution model over time is established based on the prediction model.The fatigue test data of the weathering steel welded joints in the literature are used,and the corrosion fatigue sensitivity of the weathering steel welded joints is discussed.The effect of regional location and different corrosion time and corrosion environment on its corrosion fatigue life.The results show that the area 15 mm from the longitudinal edge of the welded joint is the location of the corrosion fatigue sensitive area.With the increase of corrosion time,the corrosion degree deepens,and the corrosion fatigue life decreases continuously.(5)Based on the measured traffic flow data of a steel truss girder bridge in service,a random traffic load spectrum was established,and the stress history of the fatigue vulnerable members was obtained,and the corrosion fatigue life evaluation of the welded joints of weathering steel was carried out.Considering the effect of corrosion,the accumulation of early fatigue damage is relatively slow.With the increase of service life,fatigue damage accumulates year by year,and the deterioration effect of corrosion on the fatigue performance of bridges cannot be ignored.When the corrosion effect is not considered,the corrosion fatigue life is much greater than 100 years,and the fatigue problem is not prominent.The research results have important reference significance and value for other types of in-service steel structure bridges and new offshore and marine weathering steel bridges. |
