| Combined structural column is a kind of element that combines the advantages of pure concrete column and pure steel column,which is widely used in high-rise and super high-rise buildings.However,there are some disadvantages of this structure,such as the tendency of partial collapse and disintegration of the hoop reinforcement,and the tendency of the protective layer to fall off,resulting in reduced ductility.Compared with reinforced concrete columns,PEC columns are less susceptible to local crushing under vertical loads,while they can consume more energy and have better ductility under horizontal loads.The purpose of this paper is to expand the PEC column member forms and provide technical support for engineering applications.In order to further expand the form of cold-formed thin-walled C-shaped steel partially wrapped concrete composite column(PEC column)members,so that this new type of members to further promote the application,this paper mainly carried out the following research content:1.Three cold-formed thin-walled C-shaped rolled-edge channel steel PEC medium-length column specimens with a length of 1.5 m were designed and fabricated and subjected to axial compression tests,taking into account the effects of section size and section height-to-width ratio on the axial compression performance of the specimens.The study shows that:(1)the cross-sectional size has a small effect on the axial compression load capacity,initial stiffness and ductility coefficient of the specimens;(2)with the decrease of the cross-sectional size,the axial compression load capacity of the PEC column specimens decreases but the ductility coefficient increases,which can better predict the axial compression load capacity.By determining the parabolic boundary of the restrained concrete distribution area,the axial compression ultimate bearing capacity formula of PEC column is established and compared with the finite element analysis results,and it is found that the error is generally small and the accuracy is high,which provides a reference for the axial compression ultimate bearing capacity calculation of PEC column.2.11 cold-formed thin-walled C-shaped rolled-edge channel PEC medium-length columns of 2m length were designed and fabricated and tested for eccentricity,considering the influence of PEC column cross-sectional dimensions,eccentricity distance and spacing of the embellishment plate on the eccentricity performance of the specimens,and comparing and analyzing the validity of relevant standards for predicting the eccentricity bearing capacity of the specimens.The research shows that:(1)the cross-sectional size has a large influence on the bearing capacity of PEC column,the larger the cross-sectional size of cold-formed thin-walled C section,the larger the ultimate bearing capacity and initial stiffness,the larger the cross-sectional size,the smaller the ductility coefficient;(2)the larger the eccentricity distance,the smaller the ultimate bearing capacity and initial stiffness,with the eccentricity distance increasing from 20 mm to 40 mm,the ductility coefficient also increases,and the eccentricity distance increasing from 40 mm to 60 mm,the ductility coefficient decreases.By analyzing the distribution of the effective restraint area of the core concrete and thus calculating the yield axial force of the long PEC column section,it can be seen that:when the eccentricity distance is 20 mm and 40 mm,the yield axial force of the damaged section does not differ much from the test ultimate load,and when the eccentricity distance is 60 mm,it differs from the test ultimate load due to the local compressive damage occurred during the test.At the same time,the bending moment-axis force curves calculated by the calculation methods given by ACI318-14,AISC and EC4 are close to the measured curves of the section,and the difference with the measured curves is small.3.The finite element model of 96 groups of cold-formed thin-walled C-type rolled-edge channel PEC composite columns was established by using the finite element software ABAQUS,and the effects of column section size,eccentricity distance and spacing of embellishment plate on the eccentricity behavior of such members were considered.The stress cloud,ultimate load capacity,initial stiffness and ductility coefficient of the eccentricity test phenomenon and the finite element model of PEC column are summarized.Meanwhile,the comparison and analysis with the test results reveal that the error is generally small and the accuracy is high,which can provide some theoretical reference for the calculation of the bias compression ultimate bearing capacity of PEC columns.Through the one-way compression-bending PEC column in-plane stability bearing capacity formula given by the Technical Specification for Partially Clad Steel-Concrete Combined Structures,the N-M correlation curve of the column specimen is calculated according to the results of finite element analysis,and compared and analyzed with the actual measured curve during the test,the N-M correlation curve calculated by the finite element can be used for the prediction of the compressive bearing capacity of the PEC combined column under the action of bias load,and The prediction results are generally on the safe side. |
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