Experimental Study On Corrosion Damage Of Stay Cables’ Anchorage System Under Salt Fog Environment

As an important component of the cable bearing system bridge,the cables’ anchorage system has found a lot of damages over the years.The frequent cable breaking accidents of the bridge are also closely related to the corrosion damage of the cable steel wire in the anchorage system.Limited by the technical and economic levels,there are many shortcomings of Chinese early built suspension bridges and cable-stayed bridges in design,manufacture and installation of the anchor system,leaving great potential hazards to the safety of bridge structure.With the increasing service life,such problems are more and more evident,causing severe economic losses and bad social impacts on the country and society.Therefore,this paper,focusing on the stay cables’ anchor system of cablestayed Bridge and boom arch bridge,introduced a corrosion damage test of the stay cables’ anchor system under salt-spray environment,under the support of the National Natural Science Foundation Project "Research on corrosion fatigue damage mechanism and life prediction model of stay cable under the coupling action of alternating load and erosion environment"(No 51478071)and the National Key Research and Development Project "Monitoring and early warning system and safety risk control technology for over limit load of urban expressway bridge"(No.2017yfc0806001).The main researches and conclusions are as followers.1.Summarized and analyzed the corrosion environment,disease and detection and evaluation method of the bridge cables’ anchorage system.Based on the atmosphere and stress corrosion environment of the anchorage system,the common damages and relevant reasons were summarized,and two corrosion environments that may exist in the damaged anchorage system were analyzed.Its main test and assessment methods were summarized,and the shortcomings were analyzed2.The overall CASS test was conducted for the anchorage system of the cold cast pier head of parallel wire stay cable and cut it after the test to analyze the internal and external corrosion degree and distribution characteristics,and the reliability of the anchorage system of the cold cast pier head was studied.3.The CASS test of cable steel wire in anchorage system was carried out,and the corrosion damage mechanism and corrosion mode of steel wire in anchorage section under two kinds of corrosion environment were revealed.The stay cable wires in the anchor system and their two corrosion environments were simulated,and CASS test with different test periods was conducted for cable sections.Based on corrosion appearances of stay cable wire under different corrosion extents,the corrosion process of cable was divided into 4 stages and the corrosion extent was divided into 6 grades.4.The spatial distribution characteristics of the corrosion of the cable steel wire in the anchorage section were revealed through the comparative analysis between the experimental study and the practical bridge detection.The PE sheath and polyester fiber woven tapes of the stay cable were stripped to disperse stay cable wires,and the spatial distribution cloud diagram of the corrosion extent of the cable cross-section was drawn after the corrosion grade estimation which based on wire corrosion classification;in addition,the grey processing was conducted for the image of corroded wires by MATLAB and other image processing software to get the corrosion spatial distribution characteristics of stay cable wire,and compared with the practical bridge test results,the correctness of the test conclusion was verified.5.Experimental study on mechanical properties of corroded cable steel wire was carried out,after the tensile test and the analysis of the shape and appearance of the fracture of corrosive stay cable wires,the relationship of corrosion distribution which on the steel wire surface and the strength,ductility and fracture of the wire were revealed.6.The corrosion damage evolution model of anchorage system is proposed.Based on the particle diffusion mechanism of the porous medium and the pore structure features of stay cable wire,the dispersal pattern of corrosion factors in stay cable wires was analyzed,the corrosion factor diffusion model was established under Fick’s laws,and based on the classical calculation model of steel wire corrosion,the calculation model of cable diameter loss was established.7.Combined with the practical engineering,the application of corrosion damage evolution model of anchorage system cable was studied.Introduced the application process of the calculation model of stay cables’ wire corrosion damage in the actual detection and evaluation of stay cables’ anchorage system,and took an engineering case as an example,calculated the concentration distribution of stay cables’ corrosion factor and the distribution of diameter damage in the anchorage system in a period of time by using MATLAB,and obtained the process of stay cables’ corrosion damage.