| The reference period for most architectural designs in China is 50 years.During the early years after the founding of the People’s Republic of China,a large number of industrial and civil buildings were built,and most of their service time exceeded the design base period.Durability is not considered when designing and constructing.Most steel reinforced concrete components have durability problems such as corrosion of steel bars,cracking or spalling of protective layers,and there are various safety hazards.Part of the components may yield in the late use of irregular or sudden load.If a sudden load occurs again,such as aftershocks and secondary explosions,the structure will collapse and the rescue workers will be safe,Problems such as how to determine the maintenance and reinforcement plan in the later period must be based on the explicit determination of the yield member’s re-stress.Therefore,it is necessary to develop a study on the resistance performance of the damaged member when it is subjected to stress again.Therefore,according to the study of corroded rebar in the early stage of the research group,the mechanical properties of the secondary reinforcement of corroded rebar were first tested.Based on this,using the self-invented concrete counterforce loading test device developed by the research group,the secondary load resistance performance of the load-corroded reinforced concrete beam was studied.The main work and results are as follows:Simulate the degree of corrosion of steel bars by mechanical deficiencies,From the point of view of fracture morphology,primary strength and elongation,Simulating Steel Bar Corrosion with Mechanical System Defects is Applicability and Similarity.The secondary stressed steel shows two types of fractures,The intact steel fracture is flat and related to the depth of corrosion,the size of the unloading force,and the number of days of aging.The nominal yield strength and nominal ultimate strength of the steel bars increase with the corrosion depth of the corroded reinforcing steel under the secondary stress,and the actual yield strength and the actual ultimate strength increase,and the secondary stress of the yield strength is slightly higher than the primary stress,The analysis may simulate the "gap effect" caused by rusty pits.The steel bar was unloaded and loaded at one point in the reinforced section,and no yielding platform appeared.After age hardening,the yielding platform reappeared.In this test,the aging time of light round steel bars and ribbed steel bars was 7 days and 25 days,respectively.After ageing,each strength is further improved.After the secondary stress,the elongation of the steel bar decreases with the increase of the corrosion degree,and decreases with the increase of the load during unloading.After the age hardening,the elongation decreases slightly.A suitable physical model is established by the law of secondary mechanical properties of corroded steel bars and the characteristics of load deformation curves.This physical model is used to analyze the elastic modulus,yield strength,ultimate strength,reinforcement strain and ultimate strain of reinforcement.The mathematical model of secondary stress of corroded reinforcement with certain precondition is obtained.Based on the above results,the experiment was carried out on three load-corroded reinforced concrete beams in the tensile zone.The load level of the reinforced concrete beam in the concrete girder was 45% and the load was unloaded to 25% and the corrosion rate was 5%、9% and 11% respectively.The results show that when the concrete beam is unloaded and reloaded,the whole process is still in accordance with the assumption of flat section.In the stage of load corrosion,no new cracks appear and only the crack width increased.The cracks are all out,and the subsequent loading is unloaded and reloaded.The width of cracks in the purely curved section increases as the degree of corrosion increases.The average crack width at the beam side of the curved section does not necessarily increase with the increase of the rust degree.The load-deflection curve of the beam is almost identical to the trend of the secondary load-deformation curve of the steel bar.As the degree of corrosion increased,the increase in deflection increased,the difference in deflection at the time of yield and deflection at the limit decreased,and the ductility worsened.Measured the relationship between crack width and deformation.And there is a linear relationship between cracks and deflection.And with the extent of corrosion is increased,the slope decreased.Slope of the curve and into a straight line corrosion rate,for three beams of the present rust test.The yield load of the beam after rusting in the pull zone was compared.Same as rusted steel,the secondary yield strength increases,and the degree of improvement is almost the same as the load at unloading.And it has no direct influence and the extent of corrosion.Through theoretical analysis,different conditions may change the beam pattern of damage occurs,therefore,further research is needed. |
