Optimal design of steel frames subject to gravity and seismic codes' prescribed lateral forces

Allowable stress design of two-dimensional braced and unbraced steel frames based on AISC specifications subject to gravity and seismic lateral forces is formulated as a structural optimization problem. The nonlinear constrai ned minimization algorithm employed is the feasible directions method. The objective function is the weight of the structure, and behaviour constraint s include combined bending and axial stress, shear stress, buckling, slende rness, and drift. Cross-sectional areas are used as design variables. The a nylsis is performed using stiffness formulation of the finite element analy sis method. Equivalent static force and response spectrum analysis methods of seismic codes are considered. Based on the suggested methodology, the co mputer program OPTEQ has been developed. Examples are presented to illustra te the capability of the optimal design approach in comparative study of va rious types of frames subjected to gravity loads and seismic forces accordi ng to a typical code.