Moment modification factors for the buckling design of steel beams – new recommendations

When a unbraced flexural steel beam is subjected to a ununiform moment distribution, a simplified moment modification factor (denoted as Cb) should be evaluated for the design of the buckling resistance of that member. However, typical standards for the buckling design of steel structures (e.g., American AISC A360, Australian AS-4100, Canadian CSA S16, Eurocode 3 and Japanese standards) currently recommend different design equations for the factor. Also, such equations are based on simplified expressions those are not exact solutions. Thus, the present study firstly revise the standard equations to discuss their advantages and disadvantages in application. Also, a numerical solution based on a finite element analysis package is then conducted in the present study to predict the Cb factor. The numerical solution is successfully validated against available research results. Based on the comparison of the modification factors between of the present numerical study and those based on the design standards, it is observed that the modification factors based on the current design standards maybe not safety enough to predict the buckling resistances in several loading cases. The present study finally recommends a new modification more on the safe side for the Cb factor to ensure a conservative design