Study On Low-Cycle Constant Amplitude Reciprocating Force Performance Of Corroded Steel Bars

In recent years,earthquake disasters have occurred frequently,and concrete structures have been in service for a certain period of time.Due to various factors,internal steel bars may be corroded,and the protective layer may crack and fall off due to corrosion.If it is under earthquake,the corroded steel bar is the only bearing unit.Alternating load.However,due to the rapid damage of the corroded concrete structure under such load,the performance problems of the old concrete structure under earthquake are urgently needed.Therefore,this paper studies the behavior of low-period reciprocating load of corroded steel bars,and discusses the performance degradation law of corroded steel bars under low-cycle reciprocating load,which provides a theoretical basis for seismic performance evaluation of structural steel bars.The main work and results are as follows:1)In order to study the performance degradation law of concrete after localized pit corrosion under low-cycle reciprocating load,based on the principle of electrochemical corrosion,a test method for forming typical pit corrosion in a short time is proposed.The feasibility study of the three types of steel bars HPB300,HRB400 and HRB400 E used in the test was carried out.Based on the three-dimensional scanning technology,the pit erosion morphology and geometric information of the corroded steel bars were statistically analyzed,and the maximum cross-section loss rate of the corroded steel bars was obtained.2)Through the low-cycle reciprocating load test of three types of pitting steel bars,the variation of different pitting depths and different strain amplitudes,rebar return curve,load cycle times and energy absorption capacity are analyzed to study the three kinds of steel bars.Seismic performance.The results show that for the small strain amplitude pit corrosion steel,the section shape shows a regular 45° bevel surface,and the surface is smooth and flat.However,as the strain amplitude and the degree of corrosion increase,the fracture surface develops by local pit erosion.The effect of the fracture surface is rugged or ruptured.A brittle fracture occurs at the pitted location,which is very disadvantageous against earthquakes.When the fatigue crack width of the steel bar reaches about 0.2 mm,the tensile strength shows a significant degradation,and the tensile strength peak appears before the strain peak is reached.3)Under the small strain(less than or equal to 1.5%)reciprocating load,with the increase of the degree of corrosion,the number of load cycles and the total energy consumed by the pit corrosion steel will be seriously reduced.However,with the increase of the strain amplitude,the degree of corrosion gradually decreases,which indicates that the corrosion has a more significant effect on the performance of the steel specimen under the small strain reciprocating load.4)From the relationship between the maximum load of three different types of steel bars and the number of load cycles,it is found that the steel bars with a small degree of corrosion(the maximum section loss rate is less than 5%)are subjected to a load cycle of 65% or even 50% of the intact steel bars.Under the number of times,only the bearing capacity of the HRB400 E steel bar can reach more than 80% of its unrusted bearing capacity,and almost all the rust bar load capacity can not reach 80% of its intact state.It shows that the performance of HRB400 E corroded steel bar under low cycle reciprocating load is better than that of HRB400 and HPB300 corroded steel bar.And when the old reinforced concrete structure in the earthquake-stricken area reaches a certain service life,it can no longer be considered that its carrying capacity is a constant.When the fatigue crack width of the steel bar reaches about 0.2 mm,the tensile strength shows a significant degradation,and the tensile strength peak appears before the strain peak is reached.5)Based on the experimental data,this paper carries out statistical analysis.Based on the existing low-cycle fatigue life model of steel bars,the influence of pit depth parameters is successfully introduced,and the fatigue life model of corroded steel bars is established,and the experimental data is obtained.The anastomosis is better.