Experimental Studies On Cyclic Behavior Of Reinforcing Bars Including Buckling

It is expected that during strong earthquakes, longitudinal reinforcing steel inreinforced concrete structural elements may undergo large tension and compressionstrain reversals, if tie spacing is insufficient, this repeated loading into the inelasticrange under damaged concrete extrusion may lead to large lateral deformation ofreinforcing bars, referred to as buckling. Reinforced after buckling, it will exert a greatinfluence on reinforced concrete structural elements, especially on high pressure column.As buckling of reinforcing bars in RC members is not uncommon during seismicexcitations, proper consideration of buckling is necessary for seismic performanceevaluation. Even though the problem of reinforcement stability has been studied byseveral researchers domestic and overseas, most of these studies have been based on amonotonic behavior, limited research has been conducted considering the cyclicbehavior of reinforcing bars including buckling. Therefore, it is necessary to studycyclic stress-strain behavior of reinforcing steel including effect of buckling.The main contents of this paper are：①First the anthor completes16repeated cycle load test of reinforcing bars,emphatically analyze the effect of unsupported length-to-bar diameter ratio L/d (withL is the distance between the two supporting points of reinforced, here simulate stirrupspacing, d is representative of bar diameter) and material properties on the cyclicstress-strain behavior of reinforcing steel including effect of buckling.②Through the constrast and selection on some extensive using hysteretic modelsdomestic and overseas, introducing five classical reflect the characteristics of reinforcedcycle hysteretic model, which focuses on Monti-Nuti model and Dhakal-Maekawamodel including buckling, and use the two model validate contrast with Monti-Nutiexperiment.③Based on3D structure nonlinear analysis and performance evaluation softwarePERFORM-3D, make detailed simulation analysis on the buckling of this paper andMonti-Nuti experiment.Though the studies of reinforcing bar experiment and simulation analysis usingPERFORM-3D, the main conclusions of the study：①The inelastic buckling behavior of a reinforcing bar is very sensitive tounsupported length-to-bar diameter ratio L/d. For a given bar size, with the L/d ratio increasing, the earlier onset of buckling occurs, the more obvious buckling, thepostbuckling stress’s degenerative will be accelerated.②The postbuckling behavior of reinforcing bars also depends on the materialproperties of the steel. For a given L/d ratio, when the specimens are in reversecompression, with an increase in yield strength, the degradation of residual stressincluding buckling speed up, residual stress of HRB500is less than that of HRB335.-③The elongation of reinforcing bars under cyclic repeated loading is less than thatof steel under monotonic loading, it is related with stress state and cyclic times. Undertension-compression state, the elongation is less than that under tension-tension state;steel under tension-tension state, cyclic times are more than that under tension-compression state. The result shows reinforcing bars under tension-compressionincreasely damage.④This article focuses on Monti-Nuti model and Dhakal-Maekawa model, whichverification contrast with Monti-Nuti experiment, the results show that Monti-Nutimodel and Dhakal-Maekawa model can reasonably reflect the buckling of reinforcingbars. By contrast, Dhakal-Maekawa model which describles complete path-dependent ismore accurate.⑤Based on3D structure nonlinear analysis and performance evaluation softwarePERFORM-3D, this article takes simulation analysis of cyclic test and Monti-Nuti test.The analytical results show good agreement, meanwhile the author thinks inPERFORM-3D, if get a fix to initial stiffness, roughly take it0.35~0.4times of initialstiffness, the software can simulate the buckling of reinforcing bars more accurate.