Strength design of cruciform steel columns

Very different strengths are predicted by two different methods of designing steel cruciform columns. Both methods require design against local and flexural buckling, and while one method also requires design against torsional buckling, the other does not.Investigations of the elastic local and torsional buckling and post-buckling of cruciforms columns show that these two modes are virtually identical.The first yield and inelastic buckling approaches often used to formulate methods of designing columns against flexural buckling are extended to the torsional buckling design of cruciforms. These extensions show that it is sufficient to use local buckling design to guard against torsional buckling.It is found that design methods which make separate checks against local and torsional buckling are unnecessarily severe, and are equivalent to making the same strength reduction twice. Instead, it is sufficient to ignore the torsional buckling of cruciforms provided design checks are made against local buckling as well as flexural buckling.

► Elastic local and torsional buckling of cruciforms are virtually identical.
► Elastic local and torsional post-buckling are also virtually identical.
► Inelastic buckling and first yield analyses are made of torsional buckling.
► Only need to design cruciforms against local and flexural buckling.
► Designing cruciforms against local and torsional buckling is excessive.