Performance Of Recycled Aggregate Concrete-filled Austenitic Stainless Steel Tubular Members Subjected To Static And Dynamic Loads

Recycled aggregate concrete(RAC)-filled austenitic stainless steel tubular(FSST)structure is an innovative type of concrete-filled steel tubular structure(CFST).Combining the mechanical advantages of austenitic stainless steel and conventional CFST,RAC-FSST generally exhibits superior ductility,sufficient durability and aesthetic appearance,resulting in a promising application prospect.However,researches of RAC-FSST members in terms of the interfacial bond behavior,the capacity ultimate state,the mechanical behavior and design methods under sustained load,cyclic load and lateral impact are still limited,which requires further investigation.Thus,this dissertation conducts research works in the following four aspects:1.Push-out tests on 32 RAC-FSST specimens are conducted.The influence of salient parameters including cross-sectional size,thickness to diameter ratio and roughness of inner tube surface on the bond behavior is analyzed.On the basis of the regression analysis of the experimental data,a calculation model is suggested to determine the interfacial bond strength between the stainless steel and RAC.2.Axial compression tests on 36 RAC-FSST stub columns are carried out,and the long-term deformation of 8 specimens during 892 days is measured.The effects of the nonlinearity and strain-hardening property of stainless steel on the mechanism of composite behavior between stainless steel and RAC are investigated.The calculation models for shrinkage and creep deformation of core RAC are also determined.A finite element(FE)model for RAC-FSST under axial compression is developed,which is subsequently used to analyze the influence of material strength and steel ratio on the load-deformation relationship of RAC-FSST.The determination methods of capacity limit state,ultimate strength and influence coefficient of sustained load are proposed.Based on the collected experimental results,the partial factors for the axial compressive strength of RAC-FSST are calibrated by the reliability analysis method.3.A total of 24 RAC-FSST beam-columns are tested under cyclic loading,with another 10 RAC-FSST beam-columns tested under monotonic loading.The long-term deformation of 4 specimens is measured for 225 days,while the influence of axial compression ratio,shear span ratio,sustained load and replacement ratio of recycled coarse aggregate on the seismic performance of RAC-FSST is studied.Considering the characteristics of material loading and unloading criteria,a FE model is established to analyze the seismic performance of RAC-FSST,and the internal force development and stress distribution are discussed.Based on the parametric analysis,empirical equations are proposed to determine the bearing capacity of RAC-FSST members subjected to compression-bending and the resilience model under cyclic loading.4.A series of 36 RAC-FSST specimens are tested under lateral impact,among which the long-term deformation of 4 specimens is monitored.Effects of key parameters including impact energy,axial compression ratio,boundary conditions,shear span ratio,sustained load and replacement ratio of recycled coarse aggregate on the failure mode and time history development of impact force of RAC-FSST are studied.With material strain rate effects taken into consideration,a FE model of RAC-FSST members under lateral impact is built up.The internal force distribution,material stress and contact stress development and mechanism of energy dissipation are illustrated.On the basis of parametric analysis,the calculation method for dynamic bending capacity of RAC-FSST under lateral impact is proposed.