Study On The Axial Compression Mechanical Properties Of Rc Short Columns Reinforced With Steel Pipe Self-compacting Recycled Concrete

Reinforced concrete(RC)columns are one of the most important loadbearing elements in modern buildings,and if the load-bearing capacity is insufficient,the safety of the whole building will be endangered.In the environment of a large number of buildings entering the "aging" stage,the reinforcement of RC columns can not only improve the safety of buildings,but also comply with the concept of sustainable development of the construction industry.The method of reinforcing RC columns with steel pipe selfconsolidating recycled concrete has a good prospect in the field of reinforcement and renovation because of its good reinforcement effect,convenient construction,economic and environmental advantages.The materials in this reinforcement method can give full play to their respective advantages and make up for each other’s shortcomings,however,the research on this reinforcement method is extremely limited.Based on this,this paper investigates the axial compression mechanical properties of RC short columns reinforced by steel pipe self-compacting recycled concrete from three aspects: experimental research,theoretical analysis and finite element simulation,and the main research results and contents are as follows:(1)The proportional design of self-compacting recycled concrete and its material properties were investigated.Based on the improved full calculation method,the ratio design of the self-compacting recycled concrete was carried out by fully considering the characteristics of three types of recycled coarse aggregate replacement rates.The self-consolidated recycled concrete prepared by this ratio was tested for material properties and measured to have good working and mechanical properties,but the working and mechanical properties decreased as the replacement rate of recycled coarse aggregate increased.(2)The axial compressive mechanical properties of RC short columns reinforced with steel pipe self-compacting recycled concrete were studied.The axial compression tests of 11 reinforced columns and one unreinforced column were completed,and the effects of the strength grade of the original concrete,the thickness of the steel pipe,the replacement rate of recycled coarse aggregate,the number of layers of CFRP,and the cross-sectional diameter of the reinforced members on their mechanical properties were investigated.The test results show that the axial compressive load capacity of RC short columns strengthened by steel pipe self-compacting recycled concrete is significantly increased,which is about 2.56～5.17 times that of the original square columns.The effect of steel tube thickness,the number of outsourced CFRP layers,and the reinforced section diameter on the bearing capacity is more significant,compared to the original column concrete strength grade and the replacement rate of recycled coarse aggregate filled with self-compacting recycled concrete,which have no significant effect on the bearing capacity.The ductility and stiffness of the reinforced column are significantly increased,and the damage form is shown as ductile damage.(3)Based on the finite element software ABAQUS,a finite element model of the steel pipe self-compacting recycled concrete reinforced RC short column was established to simulate its mechanical properties under axial compression condition.Based on the accuracy of the model,the stress changes and distribution of each component during loading were analyzed,and three groups of parameters were added: the yield strength of steel pipe,the strength of selfcompacting recycled concrete,and the length to slenderness ratio of the components.The comparison between the test and finite element shows that the test data and the finite element simulation data are in good agreement and have high accuracy.The results of parameter expansion show that the ultimate bearing capacity increases significantly with the increase of steel tube yield strength;the ultimate bearing capacity increases with the increase of self-compacting recycled concrete strength,but the stiffness decreases slightly;the ultimate bearing capacity decreases with the increase of member length/slenderness ratio,but the decrease is not obvious.(4)Based on the limit equilibrium theory,the formula for calculating the axial compression load capacity of RC short columns reinforced with steel pipe self-compacting recycled concrete with high accuracy and applicability is proposed.