Research On Failure Mode And Life Prediction Of Steel Structure Coating Under Static Stress And Temperature Varying Loads

The durability guarantee of steel structures is an important consideration factor in the overall life design of bridges.When designing the entire life cycle,anti-corrosion treatment of steel structures is the key to ensuring their service life.During the use of steel bridges,due to factors such as stress and environment,the anti-corrosion coating on their surface is closely related to the steel bridge,and common deformation occurs with the load of the steel bridge.According to the Craze damage theory,coating materials will undergo local permanent damage when subjected to repeated stress and environmental factors.The climate in Gansu region is variable,with frequent sandstorms,which pose a great threat to the durability of steel bridge coatings being used in the region and have a significant impact on their service life.This article selects two different performance coating systems for coating diseases in Gansu Province to study the degradation performance of steel bridge coatings under static stress and temperature dependent loads.The material properties of steel structure coatings were obtained through tensile testing of coated specimens.Using ANSYS software,a local nonlinear model of the mid span position of a steel structure bridge was established to analyze the distribution of coating stress under dead load,live load,and temperature cyclic loads.Based on the Coffin Manson model,the service life of the coating was analyzed.A static load test device was designed based on the structural stress characteristics of steel structure coating.Coating degradation experiments were conducted on ordinary and rust resistant coating systems under the coupling effect of static load and temperature cyclic load to explore the surface degradation process and failure mode of the coating system.Combining fuzzy analysis theory,improve the evaluation method of coating systems and conduct a comprehensive evaluation of the two coating systems.The main research content and conclusions are as follows:(1)Based on the damage mechanism and deterioration influencing factors of anti-corrosion coatings both domestically and internationally,a survey was conducted on coating diseases in Gansu Province.The corrosion of steel structure coatings in Lanzhou area is relatively severe.Choosing a functional combination of different paint layers of ordinary coating system and rust conversion coating system can effectively protect steel structure bridges.(2)By conducting tensile tests on coated specimens,the stress-strain relationship,Poisson’s ratio,and elastic modulus of the steel structure coating were obtained.The results indicate that the actual steel bridge coating material is a ductile material with a yield point,and there are certain differences in the mechanical properties of each layer of paint film.The H06-X2 primer has the highest tensile strength,while the H06-C9 topcoat has the lowest.H04-A7 intermediate paint has the highest fracture strain,while H06-X2 primer has the lowest fracture strain.(3)Based on practical engineering,the coating with the highest stress at the lower edge of the bridge mid span was selected as the analysis object.A local nonlinear model of the steel structure bridge mid span position was established using ANSYS software,and the distribution law of coating stress under different working conditions was analyzed.A modified Coffin Manson model was used to establish a coating life prediction formula.The results show that the bearing capacity of the top and middle paint layers of the coating is mainly controlled by tensile stress,while the bearing capacity of the primer layer is controlled by shear stress.Dead load and temperature load are the main factors affecting the coating life,and the repeated action of live load will reduce the service life of the coating.(4)Conduct coating aging tests on steel structure coatings under the coupling effect of static load temperature cycling,and obtain the surface failure mode,adhesion loss rate,coating failure morphology,and coating thickness changes of two coating systems.The results indicate that both coating systems exhibit varying degrees of decrease in adhesion under temperature loading,and both exhibit cohesive failure modes of the primer.With the increase of static load,the degradation performance of the coating has been accelerated.The ability of the topcoat and intermediate coat to resist temperature cyclic loads is weak,and the bonding performance between the primer and the substrate provides the main protective effect.The degradation rate and degree of the rust conversion coating system are higher than those of the ordinary coating system.(5)Based on the fuzzy analysis method,a flowchart for quantitative evaluation of coating aging damage was obtained,and the factor set,evaluation set,evaluation matrix,weight set,and synthesis algorithm were determined.The rating method applicable to aging damage of steel structure protective coating system was improved.The results indicate that the evaluation model has good accuracy,high consistency with experimental results,and conforms to the laws of corrosion kinetics.