Study On The Performance Of Recycled Aggregate Concrete Filled Square Steel Tubular Long Columns Under Eccentric Compression

Recycled aggregate concrete is a green concrete material for the sustainable development of the construction industry, which has realized the recycling of waste concrete and reduced environmental pollution. The recycled aggregate concrete meets national notion about human and environment harmonious development. But, compared with the ordinary concrete, the recycled aggregate concrete has low bearing capacity, poor durability and large shrinkage and so on. In this case, in order to improve the defects of mechanical properties of the recycled aggregate concrete, experts and scholars have conducted a lot of research at home and abroad. they have found that the recycled aggregate concrete filled steel tube has good mechanical properties, which could make up for defects on mechanical properties of recycled aggregate concrete to provide a broad prospect for the practical application of recycled concrete. Research on recycled aggregate concrete filled steel tube started late in China. At present, the research about recycled aggregate concrete filled steel tube mainly focuses on axial compression, but the research on eccentric compression is relatively little.To understand the failure process and the failure mode of eccentric compression specimens in detail,8 recycled aggregate concrete filled square steel tubular long columns under eccentric compression loading have been designed to be tested step by step, in which the load bearing capacity, axial load-axial deflection carves, axial load-mid-span deflection carves of eccentric compression specimens have be obtained to study the influence of recycled coarse aggregate replacement percentage, thickness of steel tube, eccentricity and slenderness ratio on the mechanical behavior of eccentric compression specimens. At the same time, the axial load-mid-span longitudinal strain curves of eccentric compression specimens and the lateral deflection curve changes of eccentric compression specimens have be analyzed. The results of study show:(1) The failure mode of eccentric compression specimens is significantly affected by the eccentricity ratio. Most of the failure mode of specimens under large eccentricity ratio is local buckling failure, in which the ends of tube wall are serious flexion and external drum. A few of the failure mode of specimens under large eccentricity ratio is overall buckling failure, in which flexion and external drum is in the middle of specimens. The failure mode of specimens under small eccentricity ratio are local buckling failure, in which slight bending is only in the middle of specimens, and the ends of the specimen tube wall is slight flexion and external drum.(2) The recycled coarse aggregate replacement percentage has certainly influence on the load bearing capacity of eccentric compression specimens, which is in proportion to the thickness of steel tube and in inverse proportion to the recycled coarse aggregate replacement percentage, eccentricity and slenderness ratio. The eccentricity and slenderness ratio have no obviously influence on the initial axial stiffness of eccentric compression specimens, which is in proportion to the thickness of steel tube and in inverse proportion to the recycled coarse aggregate replacement percentage. The recycled coarse aggregate replacement percentage has no obviously influence on the mid-span deflection of eccentric compression specimens, which is in proportion to the thickness of steel tube, slenderness ratio and eccentricity.(3) In the elastic stage, the longitudinal strain in the tension side and in the compression side is in the compression state in the middle eccentric compression specimens. The elastic-plastic stage, the longitudinal strain in the compression side is up to yield strain in the middle eccentric compression specimens, start yielding. After reaching the ultimate load bearing capacity, the longitudinal strain is in approximately inverse proportion to the load bearing capacity in the middle eccentric compression specimens. The final failure when the longitudinal strain in the compression side is negative, the longitudinal strain in the tension side is positive.Finally, the simulation of the test process was conducted by using the finite element analysis software ABAQUS 6.10 to establish the finite element model. The load bearing capacity, the failure patterns, axial load-axial deflection carves, axial load-mid-span deflection carves of finite element simulation have obtained to be compared with the test results. The analytical results show that the finite element simulation results are in good agreement with the experimental results, verifing the reliability of finite element analysis software ABAQUS 6.10.