This paper presents a procedure for structural optimization of inelastic beam-columns consisting of base plate and Tbar stiffener under uniaxial compression. The goal of the optimization is weight minimization under ultimate strength constraint. The ultimate compressive strength of such beam-columns is calculated using geometrically exact beam theory and the nonlinear constitutive law of elasto-plastic material. These equations are discretized using finite difference spatial discretization and solved using an iterative nonlinear solver, and has been shown to agree with nonlinear finite element analysis. The design variables are cross-section geometric properties including plate width, web height, flange width and member thicknesses. A gradient-based optimization algorithm is used to search for the optimal solution. The improved ultimate strength analysis method developed in this paper can also be used to calculate accurate analytical sensitivities. The analysis, sensitivity analysis and optimization are robust and efficient. Though the focus of the present work is on deterministic design, the optimization procedure can be combined with reliability analysis procedure to perform reliability-based structural optimization for such elasto-plastic beam-columns.

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