A simplified analytical story drift evaluation of steel moment frames with radius-cut reduced beam section

A simplified analytical procedure is presented to estimate the elastic story drift of steel frames with the radius-cut RBS (reduced beam section) moment connections. Due to the geometric configuration of the radius-cut RBS, the mathematical formulation is complicated when applying the conjugate beam method to compute the component of story drift contributed by the beam. In this study, the problem is circumvented by replacing the original radius-cut RBS with an equivalent beam of constant width. The equivalence between the two is established by imposing the equal flange elongation criterion over the RBS region. This approach is justified by a finite element analysis. The story drift components contributed by the column, the panel zone, and the beam are then formulated into a closed form solution for a typical beam–column subassembly. The derived results can readily be used by designers to estimate the magnitude of RBS frame story drift and the effect of the stiffness variations.