Research On The Buckling Performance And Design Method Of Box-T Section Columns Under Compression

Box-T section columns are usually composed of one cold-formed box section and several T-sections,including L-shaped and T-shaped columns.Box-T section columns will be increasingly used in the steel structures,due to their advantages in avoiding column protrusion,increasing the usable indoor space,enhancing space utilization,and benefiting the architectural design.The research is to support the CECS standard "Technical Specification for Special-Shaped Column Structures with Box-T Section Columns".The buckling performances of box-T section columns under compression were systematically studied and new design methods were also proposed,based on the experimental,numerical,and theoretical studies.The main research work of this dissertation is as follows:(1)The elastic buckling performances of box-T section columns were firstly studied by finite element analysis,and the calculation methods of the key sectional geometric properties of open-closed sections,including principle wrapping coordinate and wrapping constant,were finally derived.Moreover,the elastic buckling strength formulas of boxT section columns were also derived.(2)The residual stress distributions of 8 different box-T section columns were measured by the sectioning method,and the practical residual stress distribution models were proposed for box-T section columns based on some reasonable simplifications and assumptions.(3)60 box-T section columns were scanned by a handheld 3D laser scanner,and the methods of scanning data processing and geometric imperfection extraction were proposed.The geometric imperfection distribution characteristics were analyzed based on the measured geometric imperfections.(4)22 box-T section columns were axially loaded while 38 box-T section columns were eccentrically loaded,and the buckling modes and ultimate loading capacities of the box-T section columns were obtained.Finite element models with material nonlinearity,initial geometric imperfections,and residual stresses considered were established for boxT section columns under axial or eccentric compression,and the accuracy of the modelling method was validated by the experimental results.(5)The effects of initial geometric imperfections,residual stress,and number of stiffeners on the buckling performances of box-T section columns were investigated by the numerical method.1540 box-T section columns under axial compression were simulated,covering the commonly used column section widths and column effective lengths in the steel residential buildings.The numerical results were compared with the design curves in the current design codes,and the selections of the design curves were recommended for box-T section columns.Moreover,new design curves were also fitted based on the Perry-Robertson formula.Finally,reliability analysis was conducted for the recommended and fitted design curves.(6)The elastic lateral buckling formulas of box-T section beams were firstly derived and the design methods of box-T section beams were proposed based on the numerical results of 858 box-T section beams.Moreover,the design methods for beam-columns in GB 50017-2017 and EN 1993-1-1 were assessed based on the numerical results of 4752beam-columns under uniaxial bending and 2880 beam-columns under biaxial bending,and the safe and reliable design methods for beam-columns were proposed.