Optimum design of unbraced rigid frames

Abstract

In this paper, an algorithm is presented for the optimum design of unbraced rigid frames which takes into account the non-linear response of the frame due to the effect of axial loads. It considers sway constraints and combined stress limitations in the design problem. While the optimality criteria approach is employed to handle sway limitations, the combined stress constraints are reduced to non-linear equations of the design variables. The algorithm initiates the design process by carrying out non-linear analysis of the frame. It checks the overall stability in every iteration of the analysis. When the non-linear response of the frame is obtained without loss of stability, the new values of design variables are computed from the recursive relationships. This process of re-analysis and re-sizing is repeated until the convergence is obtained. A number of tall steel frames are designed by the algorithm as examples.