The paper presents the stiffness analysis and optimization of stepped columns constituting the core frame of the industrial building. The two-span cross section of a one- storey industrial building is investigated herein. The quasi-static calculation is performed using the limited load approximation method for the cross-section of the most loaded middle column. The critical Euler characteristic of the compressive longitudinal load is determined by the differential bending equations at the bifurcation instability in the column sections. The parameter optimization of the column cross-section is achieved through the nonlinear mathematical programming. The optimization of medium column cross-section is considered using the proposed calculation when setting a set of constraints for the optimization task.