Experimental Study On Low-Cycle Fatigue Behavior Of HRB400E/316L Hot-Rolled Ribbed Bars Of Carbon Steel And Stainless Steel Compound Bars

With the advantages of excellent mechanical properties,economical cost as well as the convenient supply of raw materials,reinforced concrete(RC)structures are widely used in civil engineering.In the fields of transportation engineering and marine engineering,the working environment of reinforced concrete structures is characterized by strong corrosivity and the corrosion of steel bars will seriously affect the safety and durability of related structures.To improve the corrosion resistance of steel bars and control the production cost meanwhile,the hot-rolled ribbed bars of carbon steel and stainless steel compound bar(HRBSC)was proposed and has been widely researched.At present,most of the research on HRBSC focuses on the corrosion resistance property and process technology,and research on the mechanical properties especially the low-cycle fatigue properties of HRBSC is rather limited.However,under extreme disasters such as tsunami,rare and super rare earthquakes,the longitudinal steel bars in plastic hinge zone will undergo cyclic loads with large strain amplitude and suffer low-cycle fatigue failure.As a result,it is of great significance both in theory and practice to investigate the low-cycle fatigue properties of HRBSC for the disaster resilience analysis and assessment of related RC structures.Against this background,the basic mechanical properties,low-cycle fatigue properties and the strength degradation with fatigue damage accumulation of a type of HRBSC with HRB400 E core and 316 L cover were investigated in this paper,through uniaxial tensile test and a series of low-cycle fatigue tests.The main research contents and conclusions of this dissertation are as follows:(1)Uniaxial tensile test was conducted on the HRBSC and HRB400 E bars with 3 nominal diameters to investigate the yield stress,ultimate stress and elongation.The results showed that HRBSC possesses excellent mechanical properties with the requirements of Chinese code for seismic design and buildings well satisfied,hence,the HRBSC can be used as longitudinal bars in seismic resistance structures.(2)Through a series of fatigue tests,with buckling taken into account,the low-cycle fatigue properties of HRBSC and HRB400 E bars as well as the strain rate on fatigue property of HRBSC were investigated.Test results showed that HRBSC possesses excellent low-cycle properties.It is also found that only under small strain amplitude,strain rate has obvious effect on the fatigue life of HRBSC bars,and under large strain amplitude,the effect of strain rate is quite limited.(3)Based on the statistics and analysis of test results,the low-cycle fatigue life evaluation formulas for HRBSC and HRB400 E bars,the relationship between ultimate stress and fatigue damage accumulation as well as the relationship between stress amplitude and fatigue damage accumulation were proposed with the consideration of buckling.It is found that there is no essential difference between HRBSC and HRB400 E bars on strength degradation.For the two types of bars,the degradation of ultimate stress and stress amplitude varies significantly with the change of strain amplitude.When the strain amplitude is smaller than 2%,no obvious degradation of ultimate stress and stress amplitude can be observed before the fatigue damage accumulation coefficient growing up to 0.9,while when the strain amplitude exceeds 2%,serious strength degradation will continuously occur until fatigue fracture.