In this paper, an algorithm is presented for the optimum design of unb
raced rigid frames which takes into account the non-linear response of
the frame due to the effect of axial loads. It considers sway constra
ints and combined stress limitations in the design problem. While the
optimality criteria approach is employed to handle sway limitations, t
he combined stress constraints are reduced to non-linear equations of
the design variables. The algorithm initiates the design process by ca
rrying out non-linear analysis of the frame. It checks the overall sta
bility in every iteration of the analysis. When the non-linear respons
e of the frame is obtained without loss of stability, the new values o
f design variables are computed from the recursive relationships. This
process of re-analysis and resizing is repeated until the convergence
is obtained. A number of tall steel frames are designed by the algori
thm as examples. (C) 1998 Published by Elsevier Science Ltd. All right
s reserved.