Research On Design Indexes And Material Property Of Low-yield-Point Steel

Low-yield-point steel has been widely used in energy dissipation to bear seismic loads,for the advantages of its low yield strength,good ductility and excellent energy dissipation capacity.As a new type of steel,low-yield-point steel has been found that the mechanical properties are quite different from those of other structural steels.At present,the production of low-yield-point steel is still in the early stage,which is lack of relevant studies.Therefore,it is necessary to conduct a comprehensive search on the mechanical properties of low-yield-point steel.Based on the compilation of Technical specification for application of low-yield-point steel,this paper analysed the material properties comprehensively through factory investigation and experiments,furthermore,the cyclic constitutive model and the fatigue life prediction model have also been proposed.And the main contents of this paper are as follows:(1)The material properties of low-yield-point steels(LYl10、LY160、LY225)producted in Angang Steel Company were studied,and 426 groups of effective data were collected,including the yield strength,tensile strength,elongation,impact work and et al.The statistical parameters of each material properties were obtained,and the influence of the thickness of steel plate has been studied too.Furthermore,the statistical parameters of material uncertainty of domestic low-yield-point steel were calculated considering the influences of loading rate and the compliance of the testing machine.(2)The statistical parameters of the geometry and the model uncertainty were determined firstly.Based on the results above,the statistical parameters of resistance uncertainty of domestic low-yield-point steel are obtained.On the basic of the first-order second-moment method and the software Matlab,considering the uncertainty of loads,the coefficients of resistance of low-yield-point steels used in buckling restrained brace were further obtained.(3)A series of tests of LY100、LY160、LY225 low-yield-point steels have been conducted with various loading programs,including monotonic loading and cyclic loading.And the monotonic performance,hysteretic behavior and ductility performance were studied.Based on the data of experiments,the cyclic constitutive models of low-yield-point steels were proposed respectively according to Chaboche model and Hu model.Furthermore,the accuracy of constitutive models was verified through the software ABAQUS.The results showed that both the constitutive models can exactly predict the elastic-plastic mechanical behavior of low-yield-point steels,which can be effectively used in the design and calculation of engineering.(4)A series of low cyclic fatigue tests of domestic low-yield-point steel with different strain amplitude has been conducted.And the cyclic stress response characteristics of LYP were studied and the fitting curves of cyclic stress-strain were obtained based on the data of tests.The prediction models of low cyclic fatigue life for low-yield-point steel were proposed with Manson-Coffin model and Kuroda model,which have been verified to be reliable.