Static Behavior Of Recycled Aggregate Concrete Filled Circular Steel Tubular Columns

Reusing the crushed waste concrete as recycled coarse aggregate (RCA) inproducing the recycled aggregate concrete (RAC) reduces the disposal of wasteconcrete in landfills as well as the consumption of natural resources. Despite ofthese, the application of RAC in structures is limited due to its low strength and highshort-and long-term deformations. Encasing RAC into steel tube makes it possibleto expand the use of RAC as a structural solution because the mechanical behaviourof RAC will be improved as a result of the confinement effects and sealedenvironment provided by the outer steel tube. Meanwhile, the scatter of themechanical properties of recycled aggregate concrete filled steel tubular (RACFST)columns will be reduced due to the contribution of the steel tube. Up to date,extensive efforts have been dedicated to the compressive behaviour of the axiallyloaded RACFST stub columns. As an innovative structural member, limitedattention has been devoted to the compressive behaviour of the RACFST slendercolumns. This paper intends to provide the experimental and numerical analysis onthe static responses of RACFST columns under axial and eccentric loadings.As part of this work, the experiments for the15RACFST columns under axialcompressive loading were carried out to investigate the axial load versus axialshortening (circumferential deformation) responses, the axial load versus lateraldeflection responses and the failure modes of the specimens. Slenderness ratio andthe source of aggregate were considered in the tests to evaluate the influence on theaxial compressive rigidity, bearing capacity and ductility of the specimens by thesefactors.Another series of experiments were also conducted on39RACFSTbeam-columns under eccentric compressive loading to investigate their compressiveresponses which is the same as the aforementioned in the tests of the axially loadedspecimens. Besides, the assumptions of ‘the deflection curve of the member is a halfsine wave’ and ‘cross-sections remain plane’ under the whole loading process havebeen verified by the test results. Different slenderness ratio, load eccentricity ratio,RCA replacement ratio and ratio of steel area over concrete area were considered inthe experiments to evaluate how these parameters influence the compressiveresponses of these specimens.Fiber-based model was developed by numerical programming to analyze thebehaviour of RACFST slender columns under the combined actions of axialcompression and bending moment. The reliability of the numerical results was thenverified by the experimental results. An extensive parametric analysis was conducted to investigate the compressivebehaviour of RACFST slender columns. Considered parameters include theslenderness ratio, RCA replacement ratio, ratio of steel area over concrete area andyield strength of steel tube. Besides, the results of the tests presented herein werecombined with those from previous studies, and compared with existing designprovisions for concrete filled steel tubular columns with conventional concrete. Thedesign expressions from current European, American, Japanese, British and ChineseStandards were assessed. On the basis of the comparisons, design recommendationsfor RACFST slender columns under axial and eccentric loadings have been putforward.