Multiple fully stressed designs of steel frame structures with semi-rigid connections

A fully stressed design of a frame structure, in which each member is performing to its maximum safe level under at least one loading case, is a common goal in structural design. When multiple fully stressed designs are possible, the designer must make some decisions regarding the desired load path because the outcome of the iterative fully stressed design computation depends upon the initial starting design selected. When steel frame structures are modelled as having semi-rigid beam-to-column connections, the connection flexibility has a significant impact on the nature and diversity of potential fully stressed designs. This paper presents a computational study of how the variety of potential fully stressed designs is affected by connection flexibility. A numerical algorithm, which combines the stress ratio method and Newton's method to avoid problems associated with each method when used alone, is applied to generate sets of distinct fully stressed designs as connection flexibility is varied. It is found that as the connections become increasingly flexible, the variety of fully stressed designs diminishes. Load paths that are efficient with rigid connections are not realizable with semi-rigid connections because of limited bending moment transfer capacity and, consequently, limited alternate load paths. Copyright (C) 2003 John Wiley Sons, Ltd.