This paper presents a genetic algorithm based optimum design method for mul
ti-storey non-swaying steel frames with different types of bracing. The des
ign method obtains a frame and bracing system with the least weight by sele
cting appropriate sections for beams, columns and bracing members from the
standard set of steel sections. The algorithm accounts for serviceability a
nd strength constraints as specified in BS 5950 (1990). The serviceability
limit state included in the design problem is achieved by limiting the over
all and intermediate storey drift in the building to height/300 as specifie
d by the code. The strength constraints are in the form of inequalities as
given in BS 5950 which ensures that the design capacity of the member is gr
eater than the ultimate force it is subjected to. The design algorithm take
s into account lateral torsional buckling of frame members, if they are bea
m-columns. Bracing members are considered to be made out of back-to-back do
uble equal-leg angle attached to gusset plates. The algorithm presented is
used to design a number of tall frames with different bracing systems such
as X, V and Z bracing. It is noticed that X-bracing produces the lightest f
rame among the others. (C) 2001 Elsevier Science Ltd. All rights reserved.