| Hollow concrete-encased concrete filled steel tubular(CFST)columns have the advantages of open cross-section,light weight,and good ductility,which can meet the needs of large span,towering,heavy load and harsh environment in bridge structures,and have been applied in the main arch and high pier of bridges.The use of internal octagonal steel plate instead of internal longitudinal reinforcement can be used as internal formwork to simplify the construction during casting,and the internal steel plate can provide support for concrete to improve the ductility of the member.However,there is no research on the basic mechanical properties of square hollow concrete-encased CFST column with internal steel plate.Meanwhile,there is no relevant code to provide reference.In order to accurately predict the bearing capacity of square hollow concrete-encased CFST columns with internal steel plate under axial and eccentric compression,the mechanical behaviour of short members under axial compression were experimentally and numerically investigated.The mechanism and parameters of the beam-columns were carried out in this paper.The main research contents and results include:(1)Four square hollow concrete-encased CFST columns with internal steel plate were tested in axial compression.For comparison,four square hollow concrete-encased CFST columns,four reinforced concrete(RC)composite columns with internal steel plate,and two RC columns were tested.The damage mode of each specimen under axial compression and the effects of internal steel plate and CFST components on the ductility,stiffness and bearing capacity of the stacked columns were investigated.Results showed that the damage mode of each type of short column is similar to each other,showing the bulging of the middle section in the specimen and accompanied by concrete spalling.(2)Based on the ABAQUS finite element software,the finite element models of the square hollow concrete-encased CFST columns with internal steel plate and the related comparative members under axial compression were established.Based on the verified models,the stress mechanism of the typical members such as the whole process of stress and contact action of each component was studied.Meanwhile the parametric analysis of 81 square hollow concrete-encased CFST members with internal steel plate were also carried out.The effects of cross-sectional dimension,concrete strength inside and outside the steel tube,steel strength as well as the distribution of longitudinal reinforcement and steel tube on the axial compression,stiffness and ductility were emphatically analyzed.Results showed that all components worked well together during the whole load process;the cross-section size and concrete strength had significant effects on the axial performance of the member,while the effects of steel strength and steel quantity distribution were insignificantly.(3)The finite element model of square hollow concrete-encased CFST beam-columns with internal steel plate were established.The analysis focused on the force characteristics of typical members under various pressure conditions,the whole process of force and the internal force distribution of each component.Meanwhile,the influences of CFST component ratio D/B,eccentricity ratio e/B and length/slenderness ratio λ on the beam-columns,and the Nu-Mu correlation curve of members were studied.Simultaneously,the bearing capacities and Nu-Mu correlation curves of hollow concrete-encased CFST beam-columns with internal steel plate and the correlation members were compared.The results showed that,within the range of the parameters studied in this paper,the balanced failure of each beam-column occured at the eccentricity e/B=0.75 and the bearing capacity of beam-columns increased with the increase of D/B,while decreased with the increase of e/B and λ.(4)Based on the test and parameter analysis results,the design method of axial compression load capacity of square hollow concrete-encased CFST column with internal steel plate was proposed in combination with relevant codes at home and abroad.The equivalent section method was used to suggesting the formula for calculation of combined compression and bending load capacity at different neutral axis positions of such members.The results showed that the formula for calculating the axial compression and combined compression and bending load capacity could yield good prediction of square hollow concrete-encased CFST beam-columns. |
