| Reinforced concrete structures are widely used in various civil engineering fields due to its excellent properties.However,inevitable aging damage occur during the service of reinforced concrete structures.Previous studies suggested that corrosion is one of the most important factors affecting the durability of reinforced concrete structures.Localized corrosion is the most common form.The local corrosion decreases the effective sectional area and the strength and ductility of steel bars,ultimately reducing the bearing capacity of structures.In addition,the fatigue test results of steel indicated that the fracture of the material mainly occurs in the corrosion pit position,and the pit erosion has great influence on the formation and development of fatigue crack.On the other hand,the local rust in the rust pits easily lead to stress disturbances,resulting in the vicinity of rust pits stress concentration phenomenon.In order to study the influence of the stress concentration of the rust pit on the mechanical properties of the reinforcing bar,this paper simulates the local corrosion shape by artificially cutting the notch on the steel surface,and analyzes the influence of the rust pit shape and the three dimensions on the mechanical properties of the rebar.On this basis,the corresponding finite element model was established to verify the analysis,the main work was as follows:(1)Axial static tensile and axial fatigue tensile tests of different notches types of rebar were carried out.To make a batch of steel samples with different notches shape and three dimension notches,the appropriate measuring equipment was selected according to the specification and the test loading system was determined.The surface stress concentration coefficients of notched steel bars with different shapes and dimensions were measured by static tensile test,and the quantitative relationship between the yield load and ultimate load and notch depth was obtained.The functional relationship between the fatigue life and notch depth of the steel bar under the stress level of three groups,the functional relationship between the depth to width ratio of the triangle notches and the length to width ratio of the circular notches,were regressed by the axial fatigue tensile test.and the fatigue curve equation of the stress range-fatigue life-notch depth of four kinds of notched steel bars was established.(2)The stress state near the notch is numerically simulated and analyzed.A solid model of the same geometrical shape and three dimensional notched steel bar was established using finite element analysis software ANSYS.The mesh was divided into three-dimensional solid model by using fine grid partitioning technique.According to the finite element model,the stress concentration coefficient measured by the test was tested,the distribution of Mises principal stress near the notch was analyzed,and the cause of the ductility reduction of the steel bar specimen was explained preliminarily.(3)The expression of surface stress concentration coefficients related to notch shape,three dimensional and spatial distribution was established.The empirical expression of stress concentration coefficient Kto of single axial elliptic notch was established by using MATLAB corresponding toolbox.The relationship between the stress concentration coefficient of the triangular notch was established,the relationship between the stress concentration coefficients of the 0° biaxial elliptical notch and the stress concentration coefficient of 90° and 180° biaxial elliptic notch were established by the correlation coefficient α,β,φ and θ.The relationship between the ratio of the stress concentration coefficient of the two elliptic notches with ortho position,the ratio of the stress concentration coefficient of the two elliptic notches with 180 degrees to the single axial elliptic notch and the notch depth d were simply analyzed. |
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