ABSTRACT
The steel design methods used in the United States are allowable stress design (ASD), plastic
design (PD), and load and resistance factor design (LRFD). In ASD, the stress computation is based on
a first-order elastic analysis, and the geometric nonlinear effects are implicitly accounted for in the
member design equations. In PD, a first-order plastic-hinge analysis is used in the structural analysis.
PD allows inelastic force redistribution throughout the structural system. Since geometric nonlinearity
and gradual yielding effects are not accounted for in the analysis of PD, they are approximated in
member design equations. In LRFD, a first-order elastic analysis with amplification factors or a direct
second-order elastic analysis is used to account for geometric nonlinearity, and the ultimate strength of
beam-column members is implicitly reflected in the design interaction equations. All three design
