Damage Behavior Of Track Slab Under Non-uniform Corrosion Condition Of Steel Bars

The ballastless track structure is exposed to the natural environment for a long time.It not only bears the train load and temperature gradient,but also is eroded by the chemical substances in the environment,causing the steel bars to rust,which leads to cracking of the track slab.While research results on the corrosion of steel in concrete abound,there are few researches on the rust expansion cracking of track slabs.In order to study the rust and cracking characteristics of the track slab,the boundary conditions as well as material parameters in the mechanical analysis model are determined,and the concrete constitutive model and the load loading method are selected based on the characteristics of reinforcement corrosion in the concrete and the design characteristics of the track slab.Based on the above results,the mechanical analysis model of the damage of the track slab under the non-uniform corrosion condition of the steel bar are established.Based on the mechanical analysis model of track slab and by controlling the radial displacement of rust,the growth law of rust expansion crack of the track slab and the critical radial displacement of the crack are obtained.The effects of steel bar diameter,concrete cover and concrete tensile strength on rust expansion cracking were analyzed,and the critical radial displacement calculation formula was obtained by regression analysis.The rusting damage behavior of the track slab under the train load and the temperature load are analyzed.The critical displacement of the track slab under the train load and temperature load is calculated.The results of this study are as follows:(1)The rust crack of the track slab is inverted “T” type,and the crack is divided into the following stages: crack initiation,internal crack,internal crack growth,external crack,internal and external crack growth.The critical displacement of internal crack is 0.002 mm and the critical displacement of the external crack is 0.016 mm.(2)The calculation formula of critical radial displacement of internal crack and external crack shows that the critical radial displacement of cracking is positively correlated with concrete tensile strength and concrete cover,and negatively correlated with steel diameter.In order to suppress the crack damage of the track slab,under the premise of meeting the structural design requirements,small-diameter steel bars should be used as much as possible,the thickness of the concrete cover should be increased,and the concrete with high tensile strength should be used.(3)When the train load acts on the track slab,both internal and external cracks are developed.When the train load acts on the middle of the two steel bars,the critical radial displacement of the external crack is reduced to 0.015 mm;when the train load acts on the steel bar,the critical displacement of the external crack is reduced to 0.012 mm.(4)Both positive temperature gradient and negative temperature gradient will aggravate the damage of the track slab.With the additional effect of temperature gradient,the stronger the constraint,the larger the lateral damage and the smaller the vertical damage.Negative temperature gradient can induce the formation of external cracks;positive temperature gradient will increase the existing damage,but will not induce the formation of external cracks.Affected by the negative temperature gradient,the critical radial displacement of the external crack is reduced to 0.012 mm;with the effect of the positive temperature gradient,the critical radial displacement of the external crack is unchanged.