ABSTRACT
The limit-states design of beam-columns in building frames has been a subject of research interest for more than 20 years. Most current design methods are based on interaction equations which, through a combination of analytical and empirical means, fit the ultimate strength of an individual member considering the effects of geometric imperfections and residual stresses. Beam-column interaction equations can estimate quite accurately the load carrying capacity of a simplysupported beam-column with equal external loads applied at both ends. To generalize the equations such that they may be applied for members with other loading and boundary conditions, and for members in general frameworks, certain factors that approximate the actual behavior must be introduced. The effective length is a key factor that has been employed in many design methods to estimate the influence of the overall framework on the strength of a component beamcolumn member. If beam-column design is employed based on linear, first-order elastic analysis, another important factor is the amplification of first-order moments to account for second-order effects.
