Study On Effective Length Factors Of Built-up Stepped Columns

Stepped column takes mainly effective length factors of its each column section to describe the buckling load. The effective length factor ? is the ratio of the effective length l0 versus the geometric length of l, which is used to describe the equivalent degree for geometric length of axial compression members with different end constraints bearing the buckling critical load Pcr and the members with hinged rod, the value of the factor ? is significantly important.Open-web section height h>1m of built-up high-strength steel stepped column,which has more stronger plane lateral stiffness and torsional stiffness, but there is a obvious defect, that is the adverse effects of shear deformation to effective length factor,which generated by the shape of section and batten elements system could not be ignored, in other words, negative effects on critical load can be observed wherever a shear deformation is presented. Besides, a large number of studies show that,high-strength steel is helpful to improve the stability and bearing capacity of component,it may be appropriate to consider the favourable effect on the effective length factor.Furthermore, the effects of the constraint stiffness of beam between column, initial bending, inter-column restraint and lattice struts system, which could be considered for the factor ?.Stability design of built-up stepped column determined from its effective length factor of each section as solid, and "Code for Design of Steel Structures" did not provide the relevant provision of the calculation formula with considering the effects of aforementioned elements, but the method to be customary to make the moment of inertia Ix multiplied by reduction factor 0.9 in order to consider the shear deformation has less little effect on the value of stepped columns. It is not applied any longer.This thesis focused on advancing the revised method to calculate effective length factors of build-up high-strength steel stepped columns by considering the coefficient ofshear deformation and the effects of interactions among high-strength steel, initial bending and inter-column restraint at the edge between different sections in reality. It further analyzed the overall frame buckling behavior by the finite element method. The results suggest that negative effect on critical load can be observed wherever a shear deformation is presented, moreover, only strictly controlled equivalent slenderness ratio determines the effectiveness of high-strength steel. The results further suggest that the interaction among the sections of practical structure significantly reduces the buckling capacity. Therefore, the current correlation calculation in ‘Code for Design of Steel Structures' is probably not safe enough in reality. According to this thesis,there is some necessary modifications to the design method.