Study On Mechanical Properties Of GFRP Tube Confined Recycled Concrete-encased Steel Stub Columns Under Compression

Crushing the abandoned concrete into recycled aggregates to be used in recycled aggregate concrete(RAC)is an important approach to achieve the effective utilization of solid waste in construction,which is of great value of environmental protection and sustainable development.Nevertheless,numerous studies have verified the characteristics of low strength and poor durability of RAC due to the recycled aggregate.Therefore,most of the past applications of RAC were only limited to non-structural components.In order to promote the in suit application of RAC for structural purposes,it has been widely used in composite structures which have better mechanical performance.This paper presents a new composite column consisting of an FRP tube,encased steel and RAC filled in between.The FRP tube provides confinement in hoop direction,making the core RAC in a three-way compression state and leading to higher compressive strength.The buckling of the encased steel is restrained by the core concrete,hence the utilization of steel can be increased.This paper proposes an analysis model to predict the uniaxial compressive behavior of GFRP tube confined recycled aggregate concrete-encased steel short columns.Five aspects were compared with experiment date including the behavior of specimens,GFRP tubes,the core RAC,the confining stress and the contribution of each component to the bearing capacity of specimens.It was shown that the analysis model can accurately predict the behavior and the interaction between different materials of GFRP tube confined recycled aggregate concrete-encased steel short columns under uniaxial compression.In order to further study the mechanical performance of this new composite columns,a total of 21 specimens were tested under eccentric loading and the effects of the eccentricity,the replacement ratio of recycle coarse aggregate(RCA),the thickness of FRP tube,the fiber winding angle,the volume ratio of steel were investigated,respectively.The experimental phenomena and failure modes,the axial and hoop strain distribution,the load strain curve and the load deflection curve were analyzed.The conclusions are as follows: 1.Obvious characteristics can be seen before failure which caused by the rupture of GFRP tube;2.The axial strain distribution follows the stress plane section assumption and the hoop strain is larger on the compression side than that on the tension side;3.The load deformation curve of the specimens can be divided into three stages and all specimens showed excellent ductility;4.The bearing capacity generally decreased with increasing the replacement rate of RAC and the eccentricity,but enhanced with increasing the layers of GFRP tube,the fiber winding angle and the volume ratio of steel;5.The deformation was generally strengthened by increasing the replacement rate of RAC,the eccentricity and the layers of GFRP tube,but weaken with increasing the fiber winding angle and the volume ratio of steel.