Optimal design of steel frame using practical nonlinear inelastic analysis

Optimal design of steel frame using practical nonlinear inelastic analysis is developed. A practical nonlinear inelastic analysis realistically assesses both strength and behavior of a structural system and its component members in a direct manner. To capture second-order effects associated with P-δ and P-Δ moment, stability functions are used to minimize modeling and solution time. The Column Research Council (CRC) tangent modulus concept is used to account for gradual yielding due to residual stresses. A softening plastic hinge model is used to represent the degradation from elastic to zero stiffness associated with development of a hinge. A direct search method is used for minimum weight optimization. Constraint functions are load-carrying capacities and displacements. A member with the largest unit value evaluated by LRFD interaction equation is replaced one by one with an adjacent larger member selected in the database. Member sizes determined by the proposed method are compared with those given by the conventional LRFD method.