Study On Hysteretic Behavior And Seismic Damage Model Of Square Steel Tubular Recycled Concrete Composite Columns

In order to avoid excessive waste of construction resources in China and effectively solve the pollution problem of construction waste,recycled concrete has gradually emerged in everyone’s view.Its green and environmentally friendly properties provide an effective way to solve the above problems.However,defects are inevitable during the preparation process of recycled concrete,which leads to weaker mechanical properties than ordinary concrete,which greatly hinders the development and application of recycled concrete.To improve the recycling rate of building resources,this article combines recycled concrete with steel to form a composite component of square steel tube and steel reinforced recycled concrete.This type of component can effectively prevent the buckling of the wrapped steel pipe,and the construction difficulty is small.The wrapped square steel pipe can also effectively constrain the internal steel and recycled concrete,greatly improving the seismic performance of the component,and has a broad application prospect.This study conducted low cycle repeated load tests on 9 square steel tube reinforced recycled concrete composite columns,and obtained the hysteresis curve and skeleton curve of the composite columns.According to the experimental results,it can be seen that under the action of low cycle repeated loads,the failure characteristics of 9 composite columns are relatively similar.The steel pipe at the bottom of the specimen continuously bulges and deforms during the test process,until the failure occurs.The four surfaces of the steel pipe at the bottom of the composite column show obvious bulging,presenting a "circular disc" shape.The recycled concrete inside the composite column is crushed,and some of the steel pipes in the composite column even crack.The hysteresis curves of the composite columns obtained through experiments show a relatively full spindle shape,indicating that the composite column has good hysteresis performance.A finite element model of the composite column was established through Open Sees,and the experimental curve was compared with the calculated curve to verify that the relative error met the accuracy requirements.After verifying the rationality of the finite element model of the composite column,a series of parameter expansion analyses were conducted on the composite column.The results showed that the hysteresis performance of the composite column was less affected by the replacement rate of recycled coarse aggregate,the strength of recycled concrete,and the strength of steel sections.However,the bearing capacity of the composite column showed a pattern of first increasing and then decreasing with the increase of axial compression ratio;The hysteresis performance is significantly affected by the width to thickness ratio,square steel pipe strength,and steel ratio.Improving the strength of square steel pipe materials can also lead to poor ductility of composite columns;As the shear span ratio gradually decreases,the bearing capacity of the composite column significantly increases,but its ductility also deteriorates significantly,and the model failure mode develops towards brittle shear failure.In addition,this article uses a combination of theoretical derivation and data fitting to establish a skeleton curve calculation model,and further establishes its restoring force model based on the hysteresis law of the composite column.Meanwhile,based on existing damage models,this paper establishes a modified deformation and energy dissipation dual parameter damage model suitable for this type of composite column.Based on the calculation results of damage indicators,the seismic performance level of the composite column is divided,and the damage degree,failure characteristics,and displacement angle limits of the composite column under different seismic performance levels are determined.Finally,establish the corresponding relationship between the failure level,damage degree,and quantitative indicators of the composite column at various seismic performance levels.The research conclusion can provide reference for the engineering application of such components.