| To effectively alleviate the shortage of construction resources in China,recycled aggregate concrete(RAC)with green and environmental protection has become one of the hot spots in the academic field.However,the strength,deformation capacity,durability and other basic mechanical indexes of RAC were weaker than ordinary concrete,which largely limits the engineering application of RAC.To realize the recycling of construction waste and alleviate the shortage of resources,RAC was applied to composite structure,and the research on composite columns composed of RAC-filled circular steel tube and profile steel was carried out in this paper.This kind of composite columns overcomes the problems of the buckling failure of concrete-filled steel tubular columns,and the complicated construction of steel reinforced concrete columns.Besides,it also makes the circular steel tube have a good restraint effect on the core RAC and profile steel.Therefore,this kind of composite column has great earthquake resistance and engineering application prospect.In this paper,11 composite columns composed of RAC-filled circular steel tube and profile steel were designed,and the low cycle cyclic loading tests were carried out on each specimen.After that,the hysteretic curves and skeleton curves were obtained.Due to the limitations of the current finite element analysis method,considering that OpenSees has the characteristics of easy convergence,high accuracy and high applicability,the finite element model of composite columns was established by OpenSees.Moreover,The fiber division,element selection,material constitutive and solution analysis process were described in detail.After comparing the calculation curves with the experimental curves,it was found that the relative error of calculation was less than 10%,which meets the requirements of precision.On this basis,a series of parameter expansion analysis was implemented.The results showed that the hysteretic performance of composite columns was relatively less affected by the replacement ratio of RAC,strength grade of RAC and steel strength.However,increase in axial compression ratio,the hysteretic performance first increases and then decreases,and the boundary value of axial compression ratio for this phenomenon was 0.4.Futhermore,these factors,diameter thickness ratio,the strength of circular steel tube,the steel ratio and the section form of profile steel,highly confine the hysteretic behavior.In addition,the box section steel was the preferred section form,and the ductility decreases with the increase of the strength of circular steel tube.Moreover,the hysteretic behavior was significantly affected by shear span ratio.Decrease in shear span ratio,the bearing capacity of the model increases significantly,the ductility decreases at the same time.Moreover,the variation range of this trend will be more obvious with the decrease of shear span ratio.The failure mode develops towards brittle shear failure.In general,it is suggested that the design shear span ratio should be greater than 2.50.In addition,the index system for evaluating the hysteretic performance of composite columns composed of RAC-filled circular steel tube and profile steel was not perfect,so it is necessary to propose a model of restoring force suitable for this kind of composite columns.Based on the three-segment model,the calculation model of skeleton curve was established by theoretical derivation and data fitting.The process of solving yield point,peak point and limit point of the model was introduced in detail.Finally,according to the calculation model of skeleton curve and experimental hysteretic curves,the restoring force model was further established,including loading and unloading rules and hysteretic rules.The restoring force model can well reflect the characteristic points and loading and hysteretic behavior.The research conclusions can provide references for the follow-up research of this kind of composite columns. |
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