Experimental And Design Method On Axial Compressive Performance Of Partially Encased Lightweight Aggregate Concrete Composite Columns

In the background of promoting building industrialization,assembled composite components have been widely applied in practical projects with flexible forms and outstanding performance.Among them,partially encased concrete composite(PEC)column has the advantages both in terms of convenient connection method and excellent fire resistance,which catch the eyes of some scholars and engineers.On this basis,lightweight aggregate concrete will be used in PEC columns to meet the demand for assembled composite components in lightweight and easy assembly.However,owing to the high deformability of lightweight aggregate concrete,the co-working mechanisms of each part is indefinite.Hence,this paper carried out a relevant study on the axial compression performance of partially encased lightweight aggregate concrete composite(PELC)columns.The main content of this research can be described as follows:(1)The testing of 8 PELC stub columns under axial compression was conducted.The effect of concrete type,lightweight aggregate concrete strength,link spacing,longitudinal bars and section aspect ratio on the failure modes,axial load capacity and ductility of the specimens was investigated.Then,the finite element model of the PELC stub column was established via the verification of test results.The influence of key parameters including lightweight aggregate concrete strength,steel strength,link spacing,link diameter,width-thickness ratio and section aspect ratio was systematically investigated.Afterwards,the mechanical mechanism of the PELC stub column was revealed.Additionally,the contact stress and the cross-sectional stress were discussed to research the impact of the constraint effect.The results indicated that the failure mode of PELC and PEC stub columns is similar but more brittle.Besides,the mechanical properties of the column will improve with the denser link spacing and thicker link diameter.The local buckling of the flange is insignificant before peak load,but it will buckle rapidly after the outside concrete failure.Notably,the strength of the confined concrete will be improved influenced by flange and link restraint.(2)The testing of 3 PELC long columns under axial compression was conducted.The effect of slenderness ratio on the failure modes,axial load capacity and stability factors of the specimens was investigated.Then,the finite element model of the PELC long column was established via the verification of test results.The influence of key parameters including lightweight aggregate concrete strength,steel strength,link spacing and slenderness ratio was systematically investigated.Afterwards,the mechanical mechanism of the PELC long column was revealed.Additionally,the stability factors of the long columns were predicted based on the existing design rules.The results indicated that the failure modes of the long column will change from material strength damage to elastoplastic instability damage to elastic instability damage with the growth of the slenderness ratio.At the same time,the load capacity and stability factors will reduce substantially,and there will be significant longitudinal and lateral deformation of the long columns.Besides,the results calculated by the equivalent design method using code AISC 360 is conservative and accurate with the FE models.(3).In view of the limitations of the current method for calculating the axial load of PEC columns,the theoretical calculation method for assessing the axial compressive capacity of the PELC column was derived via the superposition principle and considering the effect of the confined concrete and flange buckling.The comparison showed the accuracy and applicability of the calculation method.