Steel Buildings in Europe

Part 4: Detailed Design 4 – 40 Scope It may only be adopted where:  The column is a hot rolled I or H section.  The cross-section is Class 1, 2 or 3 under compression.  The bending moment diagrams about each axis are linear.  The column is restrained laterally in both the y and z directions at each floor level but is unrestrained between the floors.  The buckling length is the same in both directions. Design criterion: Overall buckling The column must satisfy the single interactive equation: 1,0 1,5 cb,z,Rd z,Ed b,Rd y,Ed min,Rd b, Ed    M M M M N N 5.1 where: N b,min,Rd is the lesser of N b,y,Rd and N b,z,Rd N b,y,Rd and N b,z,Rd are the flexural buckling resistances about the y and the z axes M b,Rd is the lateral-torsional buckling resistance M cb,z,Rd = min y pl.z  f W for Class 1 and 2 sections and = min y el,z  f W for Class 3 sections  min =  M1 It should be noted that this equation leads to a conservative answer when Annex B of EN 1993-1-1 is used but no study has been done regarding its use with Annex A of the same standard. If this equation is not satisfied, then the more accurate expressions given in equations 6.61 and 6.62 of EN 1993-1-1 can still be used. Design criterion: Local verification For the lowest storey column, if the base is nominally pinned (as is usually the case), the axial force ratio must also satisfy: b,y,Rd Ed N N < 0,83 5.2 where: N b,y,Rd is resistance to buckling about the major axis Figure 5.12 presents a flowchart to describe this simple procedure.