Investigation On Casing Reinforcement Of Spatial Structures

The stability problem of key compression member in spatial structures receives much concern,and casing reinforcement technique,one of buckling-restrained technique,can be used to improve stability of compression member.Sleeved columns formed from casing reinforcement of compression members always have overhanging kernel segment,and sleeved columns with overhanging kernel segment are different in contact mechanism and failure modes from sleeved columns with their kernels fullyrestrained in length by their sleeves.For this,theoretical research and numerical calculation in section yield criterion and relation between internal force on critical section will be performed in this article,the main content and conclusions are as follows:Firstly,the concept of yield criterion considering cross section plasticity development(CSPD)is suggested in this article to avoid the defect in TCSY,and a way combing section analysis and component analysis is tried to establish CSPD: CSPD can stimulate plasticity development of cross section,and it shows that section yield criterion depends not only section types but also forced state of whole component.Research suggests that CSPD can describe state of stress distribution of yield section more accurately.Secondly,typical contact mechanism of sleeved columns with overhanging kernel segment is summarized,three main factors affecting mechanical properties of sleeved columns are determined: the results of finite element simulation reveal bending-moment amplification of kernel end region leading to buckling of it,effects of different parameters on mechanical properties of sleeved columns are compared.Research suggests that confinement ratio,clearance and slenderness ratio of overhanging kernel segment are three main factors affecting mechanical properties of sleeved columns.Thirdly,a simplified mechanical model for sleeved columns featuring kernel end region buckling is proposed in this article to mainly investigate the relation between kernel length of two-point contact zone and bearing capacity of sleeved columns: firstly,elastic modulus reduction factor is introduced to consider material nonlinearity of kernel;Secondly,by combing theoretical analysis and numerical analysis,confinement ratio is endowed with solid theoretical foundation,criterion to determine weather sleeves can be regarded rigid or not is advised and limit value of confinement ratio after which sleeves can be regarded rigid is given;Lastly,through theoretical analysis,a mathematic formula relating kernel length of two-point contact zone and bearing capacity of sleeved columns is established when sleeved columns works plastically and sleeves of them can be regarded rigid.Research suggests that confinement ratio has its own real meaning,when confinement ratio is greater than 1.8,sleeved columns without overhanging kernel segment will not fail at failure mode featuring overall buckling,and when confinement ratio is greater than 4,sleeves of sleeved columns without overhanging kernel segment can be regarded rigid;when slenderness ratio of overhanging kernel segment is smaller than 3,sleeved columns without overhanging kernel segment will not fail at failure mode featuring overhanging kernel segment buckling.Lastly,discontinuous bending beam model(DBB)is built to investigate axial bearing capacity of sleeved columns featuring kernel end region buckling,by combing theoretical analysis and numerical analysis,a simplified formula to calculate bearing capacity of sleeved columns featuring kernel end region buckling is obtained.Research suggests that DBB can simulate real working state of sleeved columns more accurately,it can also estimate axial bearing capacity of sleeved columns featuring buckling of kernel end region more accurately.