Performance Of Recycled Aggregate Concrete-Filled Steel Tubular Members And K-Joints Under Impact Loading

Recycled aggregate concrete(RAC)-filled steel tubular(FST)structure is a new type of composite structures which offers advantages of saving natural aggregate,desirable load-carrying performance and favorable constructability,leading to a promising prospect in engineering application.However,previous research concerning the issues of the interfacial property of RAC-FST,the stress-strain relationship of RAC,mechanical behavior of RAC-FST members and K-joints under combining effects of chloride corrosion,sustained loading and lateral impact loading are still limited.The research work achieved in this dissertation is fourfold:1.A series of push-out tests are conducted on 56 RAC-FST specimens.The bond mechanism between steel and RAC is revealed,and the key parameters affecting the interfacial property as well as their influence are determined.Based on the regression analysis of the experimental results,empirical formulas for bond strength calculation are proposed.2.A series of axial compressive tests are conducted on 38 RAC-FST stub columns.The passive confinement effect between steel and concrete is analyzed,and the compressive stress-strain model of RAC is proposed accordingly,which creates conditions for further detailed analysis of mechanical behaviors of RAC-FST members and K-joints.A finite element(FE)model is established based on experimental results.The FE model is subsequently utilized to investigate the effects of material strength,steel ratio and replacement ratio of recycled coarse aggregate on the axial behavior of RAC-FST members,and a simplified model for the ultimate strength calculation is proposed.Based on the established database of RAC-FST stub columns,the reliability index is calculated and the partial factors for the axial compressive strength are calibrated.3.A total of 25 RAC-FST members are tested in a drop hammer rig,with main parameters of replacement ratio of recycled coarse aggregate,whether to employ conditions of chloride corrosion and sustained loading,et al.The shrinkage and creep deformation of core RAC is measured for 515 days,and the influence of sustained loadimg on the structural performance of RAC-FST members is analyzed.Considering the effects of combined chloride corrosion and sustained loading,the FE model of RAC-FST member under lateral impact is built up and the feasibility of this model is verified using the experimental data.It is then employed to investiage the full-range response of RAC-FST member during the impact process.Based on the parametric analysis,a simplified model considering the effects of chloride corrosion and sustained loading is obtained to calculate the dynamic flexural capacity of RAC-FST members under impact loads.4.A total of 25 RAC-FST K-joints are tested using a drop hammer.The effects of web axial load level,chloride corrosion and sustained loading are discussed.The FE model of RAC-FST K-joints under impact loading is subsequently established and verified.The full-range respoinse of RAC-FST K-joints under conbined effects of chloride corrosion,sustained loading and impact loading is analyzed,and the structural mechanism of K-joints is summarized.On the basis of the parametric analysis,a simplified model is illustrated for the dynamic flexural capacity calculation of the chord of RAC-FST K-joints considering the combined effects,and the structural measures for the K-joints are also suggested.